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NAME

       erl_nif - API functions for an Erlang NIF library.

DESCRIPTION

       A  NIF  library  contains native implementation of some functions of an Erlang module. The
       native implemented functions (NIFs) are  called  like  any  other  functions  without  any
       difference  to the caller. A NIF library is built as a dynamically linked library file and
       loaded in runtime by calling erlang:load_nif/2.

   Warning:

       Use this functionality with extreme care.

       A native function is executed as a  direct  extension  of  the  native  code  of  the  VM.
       Execution  is  not  made in a safe environment. The VM cannot provide the same services as
       provided when executing Erlang code, such as pre-emptive scheduling or memory  protection.
       If the native function does not behave well, the whole VM will misbehave.

         * A native function that crashes will crash the whole VM.

         * An   erroneously   implemented   native   function  can  cause  a  VM  internal  state
           inconsistency, which can cause a crash of the VM, or miscellaneous misbehaviors of the
           VM at any point after the call to the native function.

         * A  native  function doing lengthy work before returning degrades responsiveness of the
           VM, and can cause miscellaneous strange behaviors. Such strange behaviors include, but
           are  not  limited to, extreme memory usage, and bad load balancing between schedulers.
           Strange behaviors that can occur  because  of  lengthy  work  can  also  vary  between
           Erlang/OTP releases.

EXAMPLE

       A minimal example of a NIF library can look as follows:

       /* niftest.c */
       #include <erl_nif.h>

       static ERL_NIF_TERM hello(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
       {
           return enif_make_string(env, "Hello world!", ERL_NIF_LATIN1);
       }

       static ErlNifFunc nif_funcs[] =
       {
           {"hello", 0, hello}
       };

       ERL_NIF_INIT(niftest,nif_funcs,NULL,NULL,NULL,NULL)

       The Erlang module can look as follows:

       -module(niftest).

       -export([init/0, hello/0]).

       -nifs([hello/0]).

       -on_load(init/0).

       init() ->
             erlang:load_nif("./niftest", 0).

       hello() ->
             erlang:nif_error("NIF library not loaded").

       Compile and test can look as follows (on Linux):

       $> gcc -fPIC -shared -o niftest.so niftest.c -I $ERL_ROOT/usr/include/
       $> erl

       1> c(niftest).
       {ok,niftest}
       2> niftest:hello().
       "Hello world!"

       In  the example above the on_load directive is used get function init called automatically
       when the module is loaded. Function init in turn calls erlang:load_nif/2 which  loads  the
       NIF  library  and  replaces  the  hello function with its native implementation in C. Once
       loaded, a NIF library is persistent. It will not be unloaded until the module code version
       that it belongs to is purged.

       The  -nifs()  attribute specifies which functions in the module that are to be replaced by
       NIFs.

       Each NIF must have an implementation in Erlang to be invoked if  the  function  is  called
       before  the  NIF  library is successfully loaded. A typical such stub implementation is to
       call erlang:nif_error which will raise an exception. The Erlang function can also be  used
       as  a  fallback  implementation  if  the  NIF  library lacks implementation for some OS or
       hardware architecture for example.

   Note:
       A NIF does not have to be exported, it can be local to the module. However,  unused  local
       stub  functions will be optimized away by the compiler, causing loading of the NIF library
       to fail.

FUNCTIONALITY

       All interaction between NIF code and the Erlang runtime system is performed by calling NIF
       API functions. Functions exist for the following functionality:

         Read and write Erlang terms:
           Any  Erlang  terms  can  be  passed  to a NIF as function arguments and be returned as
           function return values. The terms are of C-type ERL_NIF_TERM and can only be  read  or
           written using API functions. Most functions to read the content of a term are prefixed
           enif_get_ and usually return true (or false) if the term is of the expected  type  (or
           not).  The functions to write terms are all prefixed enif_make_ and usually return the
           created ERL_NIF_TERM. There are also some functions to query terms, like enif_is_atom,
           enif_is_identical, and enif_compare.

           All  terms  of  type  ERL_NIF_TERM  belong  to  an  environment of type ErlNifEnv. The
           lifetime of a term is controlled by the lifetime of its environment  object.  All  API
           functions that read or write terms has the environment that the term belongs to as the
           first function argument.

         Binaries:
           Terms of type binary are accessed with the help of  struct  type  ErlNifBinary,  which
           contains  a pointer (data) to the raw binary data and the length (size) of the data in
           bytes. Both data and size are read-only and are only to be written using calls to  API
           functions.  Instances  of  ErlNifBinary  are,  however,  always  allocated by the user
           (usually as local variables).

           The raw data pointed to by data is only mutable after a call to  enif_alloc_binary  or
           enif_realloc_binary.  All  other  functions that operate on a binary leave the data as
           read-only. A mutable binary must in the end either be freed  with  enif_release_binary
           or made read-only by transferring it to an Erlang term with enif_make_binary. However,
           it does not have to occur in the same NIF call. Read-only binaries do not have  to  be
           released.

           enif_make_new_binary  can be used as a shortcut to allocate and return a binary in the
           same NIF call.

           Binaries are sequences of whole bytes. Bitstrings with an arbitrary bit length have no
           support yet.

         Resource objects:
           The use of resource objects is a safe way to return pointers to native data structures
           from  a  NIF.  A  resource  object  is  only  a  block  of   memory   allocated   with
           enif_alloc_resource.  A  handle  ("safe  pointer")  to  this  memory block can then be
           returned  to  Erlang  by  the  use  of  enif_make_resource.  The  term   returned   by
           enif_make_resource is opaque in nature. It can be stored and passed between processes,
           but the only real end usage is to pass it back as an argument to a NIF.  The  NIF  can
           then  call  enif_get_resource  and  get  back  a pointer to the memory block, which is
           guaranteed to still be valid. A resource object is  not  deallocated  until  the  last
           handle  term  is  garbage  collected  by  the  VM  and  the  resource is released with
           enif_release_resource (not necessarily in that order).

           All resource objects are created as  instances  of  some  resource  type.  This  makes
           resources  from different modules to be distinguishable. A resource type is created by
           calling enif_open_resource_type when a library is loaded.  Objects  of  that  resource
           type  can  then later be allocated and enif_get_resource verifies that the resource is
           of the expected type. A resource type can have a  user-supplied  destructor  function,
           which  is automatically called when resources of that type are released (by either the
           garbage collector or enif_release_resource). Resource types are uniquely identified by
           a supplied name string and the name of the implementing module.

           The following is a template example of how to create and return a resource object.

         ERL_NIF_TERM term;
         MyStruct* obj = enif_alloc_resource(my_resource_type, sizeof(MyStruct));

         /* initialize struct ... */

         term = enif_make_resource(env, obj);

         if (keep_a_reference_of_our_own) {
             /* store 'obj' in static variable, private data or other resource object */
         }
         else {
             enif_release_resource(obj);
             /* resource now only owned by "Erlang" */
         }
         return term;

           Notice that once enif_make_resource creates the term to return to Erlang, the code can
           choose to either keep its own native pointer to the allocated struct  and  release  it
           later,  or release it immediately and rely only on the garbage collector to deallocate
           the resource object eventually when it collects the term.

           Another use of resource objects is to create binary  terms  with  user-defined  memory
           management.  enif_make_resource_binary  creates  a  binary term that is connected to a
           resource object. The destructor of the resource is called when the binary  is  garbage
           collected,  at which time the binary data can be released. An example of this can be a
           binary term consisting of data from a mmap'ed file. The destructor can then do  munmap
           to release the memory region.

           Resource  types  support  upgrade  in runtime by allowing a loaded NIF library to take
           over an already existing resource type and by that "inherit" all existing  objects  of
           that  type.  The  destructor of the new library is thereafter called for the inherited
           objects and the library with the old  destructor  function  can  be  safely  unloaded.
           Existing  resource  objects,  of  a module that is upgraded, must either be deleted or
           taken over by the new NIF library. The unloading of a library is postponed as long  as
           there exist resource objects with a destructor function in the library.

         Module upgrade and static data:
           A  loaded  NIF  library  is  tied to the Erlang module instance that loaded it. If the
           module is upgraded, the new module instance needs to load  its  own  NIF  library  (or
           maybe  choose  not to). The new module instance can, however, choose to load the exact
           same NIF library as the old code if it wants to. Sharing  the  dynamic  library  means
           that  static  data  defined by the library is shared as well. To avoid unintentionally
           shared static data between module instances, each Erlang module version can  keep  its
           own  private  data.  This  private  data can be set when the NIF library is loaded and
           later retrieved by calling enif_priv_data.

         Threads and concurrency:
           A NIF is thread-safe without any explicit synchronization as long as it acts as a pure
           function  and  only  reads  the  supplied  arguments. When you write to a shared state
           either through static variables  or  enif_priv_data,  you  need  to  supply  your  own
           explicit synchronization. This includes terms in process independent environments that
           are shared between threads. Resource objects also require synchronization if you treat
           them as mutable.

           The  library initialization callbacks load and upgrade are thread-safe even for shared
           state data.

         Version Management:
           When a NIF library is built, information about the NIF API version  is  compiled  into
           the  library.  When  a  NIF  library  is  loaded, the runtime system verifies that the
           library is of a compatible version. erl_nif.h defines the following:

           ERL_NIF_MAJOR_VERSION:
             Incremented when NIF library incompatible changes are made  to  the  Erlang  runtime
             system.   Normally   it   suffices   to   recompile   the   NIF   library  when  the
             ERL_NIF_MAJOR_VERSION has changed, but it can, under rare circumstances,  mean  that
             NIF libraries must be slightly modified. If so, this will of course be documented.

           ERL_NIF_MINOR_VERSION:
             Incremented  when  new features are added. The runtime system uses the minor version
             to determine what features to use.

           The runtime system normally refuses to load  a  NIF  library  if  the  major  versions
           differ,  or  if  the  major  versions  are equal and the minor version used by the NIF
           library is greater than the one used by the runtime system.  Old  NIF  libraries  with
           lower  major versions are, however, allowed after a bump of the major version during a
           transition period of two major releases. Such old NIF libraries can  however  fail  if
           deprecated features are used.

         Time Measurement:
           Support for time measurement in NIF libraries:

           * ErlNifTime

           * ErlNifTimeUnit

           * enif_monotonic_time()

           * enif_time_offset()

           * enif_convert_time_unit()

         I/O Queues:
           The  Erlang  nif library contains function for easily working with I/O vectors as used
           by the unix system call writev. The I/O Queue  is  not  thread  safe,  so  some  other
           synchronization mechanism has to be used.

           * SysIOVec

           * ErlNifIOVec

           * enif_ioq_create()

           * enif_ioq_destroy()

           * enif_ioq_enq_binary()

           * enif_ioq_enqv()

           * enif_ioq_deq()

           * enif_ioq_peek()

           * enif_ioq_peek_head()

           * enif_inspect_iovec()

           * enif_free_iovec()

           Typical usage when writing to a file descriptor looks like this:

         int writeiovec(ErlNifEnv *env, ERL_NIF_TERM term, ERL_NIF_TERM *tail,
                        ErlNifIOQueue *q, int fd) {

             ErlNifIOVec vec, *iovec = &vec;
             SysIOVec *sysiovec;
             int saved_errno;
             int iovcnt, n;

             if (!enif_inspect_iovec(env, 64, term, tail, &iovec))
                 return -2;

             if (enif_ioq_size(q) > 0) {
                 /* If the I/O queue contains data we enqueue the iovec and
                    then peek the data to write out of the queue. */
                 if (!enif_ioq_enqv(q, iovec, 0))
                     return -3;

                 sysiovec = enif_ioq_peek(q, &iovcnt);
             } else {
                 /* If the I/O queue is empty we skip the trip through it. */
                 iovcnt = iovec->iovcnt;
                 sysiovec = iovec->iov;
             }

             /* Attempt to write the data */
             n = writev(fd, sysiovec, iovcnt);
             saved_errno = errno;

             if (enif_ioq_size(q) == 0) {
                 /* If the I/O queue was initially empty we enqueue any
                    remaining data into the queue for writing later. */
                 if (n >= 0 && !enif_ioq_enqv(q, iovec, n))
                     return -3;
             } else {
                 /* Dequeue any data that was written from the queue. */
                 if (n > 0 && !enif_ioq_deq(q, n, NULL))
                     return -4;
             }

             /* return n, which is either number of bytes written or -1 if
                some error happened */
             errno = saved_errno;
             return n;
         }

         Long-running NIFs:
           As  mentioned in the warning text at the beginning of this manual page, it is of vital
           importance that a native function returns relatively fast. It is difficult to give  an
           exact  maximum amount of time that a native function is allowed to work, but usually a
           well-behaving native function is to return to its caller within  1  millisecond.  This
           can  be achieved using different approaches. If you have full control over the code to
           execute in the native function, the best approach is to divide the work into  multiple
           chunks  of  work  and  call  the native function multiple times. This is, however, not
           always possible, for example when calling third-party libraries.

           The enif_consume_timeslice() function can be used to inform the runtime  system  about
           the  length of the NIF call. It is typically always to be used unless the NIF executes
           very fast.

           If the NIF call is too lengthy, this must be handled in one of the following  ways  to
           avoid  degraded  responsiveness,  scheduler load balancing problems, and other strange
           behaviors:

           Yielding NIF:
             If the functionality of a long-running NIF can be split so  that  its  work  can  be
             achieved through a series of shorter NIF calls, the application has two options:

             * Make that series of NIF calls from the Erlang level.

             * Call   a  NIF  that  first  performs  a  chunk  of  the  work,  then  invokes  the
               enif_schedule_nif function to schedule another NIF call to perform the next chunk.
               The final call scheduled in this manner can then return the overall result.

             Breaking  up a long-running function in this manner enables the VM to regain control
             between calls to the NIFs.

             This approach is always preferred over the other alternatives described below.  This
             both from a performance perspective and a system characteristics perspective.

           Threaded NIF:
             This  is  accomplished  by dispatching the work to another thread managed by the NIF
             library, return from the NIF, and wait for the  result.  The  thread  can  send  the
             result  back  to  the  Erlang  process  using  enif_send.  Information  about thread
             primitives is provided below.

           Dirty NIF:
             A NIF that cannot be split and cannot execute in a millisecond or less is  called  a
             "dirty  NIF", as it performs work that the ordinary schedulers of the Erlang runtime
             system cannot handle cleanly. Applications that make  use  of  such  functions  must
             indicate  to  the  runtime  that  the  functions  are  dirty  so they can be handled
             specially. This is handled by executing dirty jobs on a separate set  of  schedulers
             called  dirty  schedulers.  A dirty NIF executing on a dirty scheduler does not have
             the same duration restriction as a normal NIF.

             It is important to classify the dirty job  correct.  An  I/O  bound  job  should  be
             classified  as such, and a CPU bound job should be classified as such. If you should
             classify CPU bound jobs as  I/O  bound  jobs,  dirty  I/O  schedulers  might  starve
             ordinary  schedulers.  I/O  bound jobs are expected to either block waiting for I/O,
             and/or spend a limited amount of time moving data.

             To schedule a dirty NIF for execution, the application has two options:

             * Set the appropriate flags value for the dirty NIF in its ErlNifFunc entry.

             * Call enif_schedule_nif, pass to it a pointer to the dirty NIF to be executed,  and
               indicate  with  argument flags whether it expects the operation to be CPU-bound or
               I/O-bound.

             A job that alternates between I/O bound  and  CPU  bound  can  be  reclassified  and
             rescheduled using enif_schedule_nif so that it executes on the correct type of dirty
             scheduler at all times. For more information see the  documentation  of  the  erl(1)
             command line arguments +SDcpu, and +SDio.

             While  a  process executes a dirty NIF, some operations that communicate with it can
             take a very long time to complete.  Suspend  or  garbage  collection  of  a  process
             executing  a  dirty NIF cannot be done until the dirty NIF has returned. Thus, other
             processes waiting for such operations to complete might have to wait for a very long
             time.        Blocking        multi-scheduling,        that        is,        calling
             erlang:system_flag(multi_scheduling, block), can also  take  a  very  long  time  to
             complete.  This is because all ongoing dirty operations on all dirty schedulers must
             complete before the block operation can complete.

             Many operations communicating with a process executing a  dirty  NIF  can,  however,
             complete  while it executes the dirty NIF. For example, retrieving information about
             it through process_info, setting its group leader, register/unregister its name, and
             so on.

             Termination of a process executing a dirty NIF can only be completed up to a certain
             point while it executes the dirty NIF. All Erlang resources, such as its  registered
             name  and  its  ETS  tables, are released. All links and monitors are triggered. The
             execution of the  NIF  is,  however,  not  stopped.  The  NIF  can  safely  continue
             execution,  allocate  heap  memory,  and  so  on, but it is of course better to stop
             executing as soon as possible. The NIF can check whether a current process is  alive
             using    enif_is_current_process_alive.    Communication    using    enif_send   and
             enif_port_command  is  also  dropped  when  the  sending  process  is   not   alive.
             Deallocation of certain internal resources, such as process heap and process control
             block, is delayed until the dirty NIF has completed.

INITIALIZATION

         ERL_NIF_INIT(MODULE, ErlNifFunc funcs[], load, NULL, upgrade, unload):
           This is the magic macro to initialize a NIF library. It is to be evaluated  in  global
           file scope.

           MODULE is the name of the Erlang module as an identifier without string quotations. It
           is stringified by the macro.

           funcs is a static array of function descriptors for all the implemented NIFs  in  this
           library.

           load,  upgrade  and unload are pointers to functions. One of load or upgrade is called
           to initialize the library. unload is called to release the library. All are  described
           individually below.

           The  fourth  argument  NULL  is ignored. It was earlier used for the deprecated reload
           callback which is no longer supported since OTP 20.

           If compiling a NIF lib for static inclusion  through  --enable-static-nifs,  then  the
           macro  STATIC_ERLANG_NIF_LIBNAME  must  be  defined  as  the  name of the archive file
           (excluding file  extension  .a)  without  string  quotations.  It  must  only  contain
           characters  allowed  in a C indentifier. The macro must be defined before erl_nif.h is
           included. If the older macro STATIC_ERLANG_NIF is instead used, then the name  of  the
           archive file must match the name of the module.

         int (*load)(ErlNifEnv* caller_env, void** priv_data, ERL_NIF_TERM load_info):
           load  is called when the NIF library is loaded and no previously loaded library exists
           for this module.

           *priv_data can be set to point to some private data if the library  needs  to  keep  a
           state   between   NIF  calls.  enif_priv_data  returns  this  pointer.  *priv_data  is
           initialized to NULL when load is called.

           load_info is the second argument to erlang:load_nif/2.

           The library fails to load if load returns anything other than 0. load can be  NULL  if
           initialization is not needed.

         int   (*upgrade)(ErlNifEnv*   caller_env,   void**   priv_data,   void**  old_priv_data,
         ERL_NIF_TERM load_info):
           upgrade is called when the NIF library is loaded and there is old code of this  module
           with a loaded NIF library.

           Works  as  load, except that *old_priv_data already contains the value set by the last
           call to load or upgrade for the old module code. *priv_data  is  initialized  to  NULL
           when upgrade is called. It is allowed to write to both *priv_data and *old_priv_data.

           The  library  fails  to load if upgrade returns anything other than 0 or if upgrade is
           NULL.

         void (*unload)(ErlNifEnv* caller_env, void* priv_data):
           unload is called when the module code that the NIF library belongs  to  is  purged  as
           old. New code of the same module may or may not exist.

DATA TYPES

         ERL_NIF_TERM:
           Variables  of  type  ERL_NIF_TERM can refer to any Erlang term. This is an opaque type
           and values of it can only by used either as arguments to API functions  or  as  return
           values  from  NIFs.  All  ERL_NIF_TERMs  belong  to an environment (ErlNifEnv). A term
           cannot be destructed individually, it is valid until its environment is destructed.

         ErlNifEnv:
           ErlNifEnv represents an environment that can  host  Erlang  terms.  All  terms  in  an
           environment  are  valid  as  long  as the environment is valid. ErlNifEnv is an opaque
           type; pointers to it  can  only  be  passed  on  to  API  functions.  Three  types  of
           environments exist:

           Process bound environment:
             Passed  as  the  first  argument to all NIFs. All function arguments passed to a NIF
             belong to that environment. The return  value  from  a  NIF  must  also  be  a  term
             belonging to the same environment.

             A  process bound environment contains transient information about the calling Erlang
             process. The environment is only valid in  the  thread  where  it  was  supplied  as
             argument  until  the NIF returns. It is thus useless and dangerous to store pointers
             to process bound environments between NIF calls.

           Callback environment:
             Passed as the first argument to all the non-NIF callback functions  (load,  upgrade,
             unload,  dtor,  down,  stop and dyncall). Works like a process bound environment but
             with a temporary pseudo process that "terminates" when the  callback  has  returned.
             Terms may be created in this environment but they will only be accessible during the
             callback.

           Process independent environment:
             Created by calling enif_alloc_env. This environment  can  be  used  to  store  terms
             between  NIF  calls  and  to  send  terms  with  enif_send.  A  process  independent
             environment with all its terms is valid until  you  explicitly  invalidate  it  with
             enif_free_env or enif_send.

           All  contained  terms  of  a list/tuple/map must belong to the same environment as the
           list/tuple/map itself. Terms can be copied between environments with enif_make_copy.

         ErlNifFunc:

         typedef struct {
             const char* name;
             unsigned arity;
             ERL_NIF_TERM (*fptr)(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
             unsigned flags;
         } ErlNifFunc;

           Describes a NIF by its name, arity, and implementation.

           fptr:
             A pointer to the function that implements the NIF.

           argv:
             Contains the function arguments passed to the NIF.

           argc:
             The array length, that is, the  function  arity.  argv[N-1]  thus  denotes  the  Nth
             argument to the NIF. Notice that the argument argc allows for the same C function to
             implement several Erlang functions with different arity (but probably with the  same
             name).

           flags:
             Is  0  for a regular NIF (and so its value can be omitted for statically initialized
             ErlNifFunc instances).

             flags can be used to indicate that the NIF is a dirty NIF that is to be executed  on
             a dirty scheduler thread.

             If  the  dirty  NIF  is  expected  to  be CPU-bound, its flags field is to be set to
             ERL_NIF_DIRTY_JOB_CPU_BOUND or ERL_NIF_DIRTY_JOB_IO_BOUND.

       Note:
           If one of the ERL_NIF_DIRTY_JOB_*_BOUND flags is set, and the runtime  system  has  no
           support for dirty schedulers, the runtime system refuses to load the NIF library.

         ErlNifBinary:

         typedef struct {
             size_t size;
             unsigned char* data;
         } ErlNifBinary;

           ErlNifBinary  contains transient information about an inspected binary term. data is a
           pointer to a buffer of size bytes with the raw content of the binary.

           Notice that ErlNifBinary is a semi-opaque type and you are only allowed to read fields
           size and data.

         ErlNifBinaryToTerm:
           An  enumeration  of  the  options  that  can  be specified to enif_binary_to_term. For
           default behavior, use value 0.

           When receiving data from untrusted sources, use option ERL_NIF_BIN2TERM_SAFE.

         ErlNifMonitor:
           This is an opaque data type that identifies a monitor.

           The nif writer is  to  provide  the  memory  for  storing  the  monitor  when  calling
           enif_monitor_process.  The address of the data is not stored by the runtime system, so
           ErlNifMonitor can be used as any other data,  it  can  be  copied,  moved  in  memory,
           forgotten, and so on. To compare two monitors, enif_compare_monitors must be used.

         ErlNifPid:
           A  process  identifier  (pid).  In  contrast to pid terms (instances of ERL_NIF_TERM),
           ErlNifPids are self-contained and not bound to any environment. ErlNifPid is an opaque
           type. It can be copied, moved in memory, forgotten, and so on.

         ErlNifPort:
           A  port  identifier.  In  contrast  to  port  ID  terms  (instances  of ERL_NIF_TERM),
           ErlNifPorts are self-contained and not bound to  any  environment.  ErlNifPort  is  an
           opaque type. It can be copied, moved in memory, forgotten, and so on.

         ErlNifResourceType:
           Each  instance  of  ErlNifResourceType  represents  a class of memory-managed resource
           objects that can be garbage collected. Each resource type has  a  unique  name  and  a
           destructor function that is called when objects of its type are released.

         ErlNifResourceTypeInit:

         typedef struct {
             ErlNifResourceDtor* dtor;       // #1 Destructor
             ErlNifResourceStop* stop;       // #2 Select stop
             ErlNifResourceDown* down;       // #3 Monitor down
             int members;
             ErlNifResourceDynCall* dyncall; // #4 Dynamic call
         } ErlNifResourceTypeInit;

           Initialization structure read by enif_open_resource_type_x enif_init_resource_type.

         ErlNifResourceDtor:

         typedef void ErlNifResourceDtor(ErlNifEnv* caller_env, void* obj);

           The function prototype of a resource destructor function.

           The  obj  argument is a pointer to the resource. The only allowed use for the resource
           in the destructor is to access its  user  data  one  final  time.  The  destructor  is
           guaranteed to be the last callback before the resource is deallocated.

         ErlNifResourceDown:

         typedef void ErlNifResourceDown(ErlNifEnv* caller_env, void* obj, ErlNifPid* pid, ErlNifMonitor* mon);

           The  function  prototype  of  a  resource  down  function,  called  on  the  behalf of
           enif_monitor_process. obj is the resource,  pid  is  the  identity  of  the  monitored
           process that is exiting, and mon is the identity of the monitor.

         ErlNifResourceStop:

         typedef void ErlNifResourceStop(ErlNifEnv* caller_env, void* obj, ErlNifEvent event, int is_direct_call);

           The  function  prototype  of  a  resource  stop  function,  called  on  the  behalf of
           enif_select. obj is the resource, event is OS event, is_direct_call  is  true  if  the
           call is made directly from enif_select or false if it is a scheduled call (potentially
           from another thread).

         ErlNifResourceDynCall:

         typedef void ErlNifResourceDynCall(ErlNifEnv* caller_env, void* obj, void* call_data);

           The  function  prototype  of   a   dynamic   resource   call   function,   called   by
           enif_dynamic_resource_call.  Argument  obj is the resource object and call_data is the
           last argument to enif_dynamic_resource_call passed through.

         ErlNifCharEncoding:

         typedef enum {
             ERL_NIF_LATIN1
         }ErlNifCharEncoding;

           The character encoding used in strings and  atoms.  The  only  supported  encoding  is
           ERL_NIF_LATIN1 for ISO Latin-1 (8-bit ASCII).

         ErlNifSysInfo:
           Used  by enif_system_info to return information about the runtime system. Contains the
           same content as ErlDrvSysInfo.

         ErlNifSInt64:
           A native signed 64-bit integer type.

         ErlNifUInt64:
           A native unsigned 64-bit integer type.

         ErlNifTime:
           A signed 64-bit integer type for representation of time.

         ErlNifTimeUnit:
           An enumeration of time units supported by the NIF API:

           ERL_NIF_SEC:
             Seconds

           ERL_NIF_MSEC:
             Milliseconds

           ERL_NIF_USEC:
             Microseconds

           ERL_NIF_NSEC:
             Nanoseconds

         ErlNifUniqueInteger:
           An enumeration of the properties that can be requested from  enif_make_unique_integer.
           For default properties, use value 0.

           ERL_NIF_UNIQUE_POSITIVE:
             Return only positive integers.

           ERL_NIF_UNIQUE_MONOTONIC:
             Return  only   strictly  monotonically  increasing integer corresponding to creation
             time.

         ErlNifHash:
           An enumeration of the supported hash types that can be generated using enif_hash.

           ERL_NIF_INTERNAL_HASH:
             Non-portable hash function that only guarantees the same  hash  for  the  same  term
             within one Erlang VM instance.

             It takes 32-bit salt values and generates hashes within 0..2^32-1.

           ERL_NIF_PHASH2:
             Portable  hash function that gives the same hash for the same Erlang term regardless
             of machine architecture and ERTS version.

             It ignores salt values and generates hashes within 0..2^27-1.

             Slower than ERL_NIF_INTERNAL_HASH. It corresponds to erlang:phash2/1.

         SysIOVec:
           A system I/O vector, as used by writev on Unix and WSASend on Win32.  It  is  used  in
           ErlNifIOVec and by enif_ioq_peek.

         ErlNifIOVec:

         typedef struct {
           int iovcnt;
           size_t size;
           SysIOVec* iov;
         } ErlNifIOVec;

           An  I/O  vector  containing  iovcnt  SysIOVecs  pointing  to  the  data. It is used by
           enif_inspect_iovec and enif_ioq_enqv.

         ErlNifIOQueueOpts:
            Options to configure a ErlNifIOQueue.

           ERL_NIF_IOQ_NORMAL:
             Create a normal I/O Queue

EXPORTS

       void *enif_alloc(size_t size)

              Allocates memory of size bytes.

              Returns NULL if the allocation fails.

              The returned pointer is suitably aligned for any built-in  type  that  fit  in  the
              allocated memory.

       int enif_alloc_binary(size_t size, ErlNifBinary* bin)

              Allocates  a new binary of size size bytes. Initializes the structure pointed to by
              bin to refer to the allocated  binary.  The  binary  must  either  be  released  by
              enif_release_binary   or   ownership   transferred   to   an   Erlang   term   with
              enif_make_binary. An allocated (and owned) ErlNifBinary can  be  kept  between  NIF
              calls.

              If  you do not need to reallocate or keep the data alive across NIF calls, consider
              using enif_make_new_binary instead as  it  will  allocate  small  binaries  on  the
              process heap when possible.

              Returns true on success, or false if allocation fails.

       ErlNifEnv *enif_alloc_env()

              Allocates  a  new  process  independent environment. The environment can be used to
              hold terms that are not bound to any process. Such terms can later be copied  to  a
              process  environment  with enif_make_copy or be sent to a process as a message with
              enif_send.

              Returns pointer to the new environment.

       void *enif_alloc_resource(ErlNifResourceType*
               type, unsigned size)

              Allocates a memory-managed resource object of type type and size size bytes.

       size_t enif_binary_to_term(ErlNifEnv *env,
               const unsigned char* data, size_t size, ERL_NIF_TERM *term,
               ErlNifBinaryToTerm opts)

              Creates a term that is the result of decoding the binary data at data,  which  must
              be  encoded  according  to the Erlang external term format. No more than size bytes
              are  read  from  data.  Argument  opts  corresponds  to  the  second  argument   to
              erlang:binary_to_term/2 and must be either 0 or ERL_NIF_BIN2TERM_SAFE.

              On  success,  stores  the  resulting  term at *term and returns the number of bytes
              read. Returns 0 if decoding fails or if opts is invalid.

              See also ErlNifBinaryToTerm, erlang:binary_to_term/2, and enif_term_to_binary.

       void enif_clear_env(ErlNifEnv* env)

              Frees all terms in an environment and clears it for  reuse.  The  environment  must
              have been allocated with enif_alloc_env.

       int enif_compare(ERL_NIF_TERM lhs, ERL_NIF_TERM rhs)

              Returns  an  integer  <  0  if  lhs  <  rhs,  0 if lhs = rhs, and > 0 if lhs > rhs.
              Corresponds to the Erlang operators ==, /=, =<, <, >=, and > (but not =:= or =/=).

       int enif_compare_monitors(const ErlNifMonitor
               *monitor1, const ErlNifMonitor *monitor2)

              Compares two ErlNifMonitors. Can also be used to imply  some  artificial  order  on
              monitors, for whatever reason.

              Returns  0  if monitor1 and monitor2 are equal, < 0 if monitor1 < monitor2, and > 0
              if monitor1 > monitor2.

       int enif_compare_pids(const ErlNifPid *pid1, const ErlNifPid *pid2)

              Compares two ErlNifPids according to term order.

              Returns 0 if pid1 and pid2 are equal, < 0 if pid1 < pid2, and > 0 if pid1 > pid2.

       void enif_cond_broadcast(ErlNifCond *cnd)

              Same as erl_drv_cond_broadcast.

       ErlNifCond *enif_cond_create(char *name)

              Same as erl_drv_cond_create.

       void enif_cond_destroy(ErlNifCond *cnd)

              Same as erl_drv_cond_destroy.

       char*enif_cond_name(ErlNifCond* cnd)

              Same as erl_drv_cond_name.

       void enif_cond_signal(ErlNifCond *cnd)

              Same as erl_drv_cond_signal.

       void enif_cond_wait(ErlNifCond *cnd, ErlNifMutex *mtx)

              Same as erl_drv_cond_wait.

       int enif_consume_timeslice(ErlNifEnv *env, int percent)

              Gives the runtime system a hint about how much CPU time the current  NIF  call  has
              consumed since the last hint, or since the start of the NIF if no previous hint has
              been specified. The time is specified as a percent of the timeslice that a  process
              is  allowed to execute Erlang code until it can be suspended to give time for other
              runnable processes. The scheduling timeslice  is  not  an  exact  entity,  but  can
              usually be approximated to about 1 millisecond.

              Notice  that  it  is  up  to the runtime system to determine if and how to use this
              information. Implementations on some platforms can use  other  means  to  determine
              consumed  CPU  time.  Lengthy  NIFs  should  regardless  of  this  frequently  call
              enif_consume_timeslice to determine if it is allowed to continue execution.

              Argument percent must be an integer between 1 and 100. This function must  only  be
              called  from  a NIF-calling thread, and argument env must be the environment of the
              calling process.

              Returns 1 if the timeslice is exhausted, otherwise 0. If 1 is returned, the NIF  is
              to return as soon as possible in order for the process to yield.

              This function is provided to better support co-operative scheduling, improve system
              responsiveness, and make it easier to prevent misbehaviors of the VM because  of  a
              NIF  monopolizing  a scheduler thread. It can be used to divide  length work into a
              number of repeated NIF calls without the need to create threads.

              See also the warning text at the beginning of this manual page.

       ErlNifTime enif_convert_time_unit(ErlNifTime
               val, ErlNifTimeUnit from, ErlNifTimeUnit to)

              Converts the val value of time unit from to the corresponding value  of  time  unit
              to. The result is rounded using the floor function.

                val:
                  Value to convert time unit for.

                from:
                  Time unit of val.

                to:
                  Time unit of returned value.

              Returns ERL_NIF_TIME_ERROR if called with an invalid time unit argument.

              See also ErlNifTime and ErlNifTimeUnit.

       ERL_NIF_TERM enif_cpu_time(ErlNifEnv *)

              Returns  the CPU time in the same format as erlang:timestamp(). The CPU time is the
              time the current logical CPU has spent executing since some arbitrary point in  the
              past.  If  the  OS  does  not  support  fetching  this value, enif_cpu_time invokes
              enif_make_badarg.

       int enif_demonitor_process(ErlNifEnv* caller_env,
             void* obj, const ErlNifMonitor* mon)

              Cancels a monitor created earlier with  enif_monitor_process.  Argument  obj  is  a
              pointer to the resource holding the monitor and *mon identifies the monitor.

              Argument  caller_env  is  the  environment  of the calling thread (process bound or
              callback environment) or NULL if calling from a custom thread not spawned by ERTS.

              Returns 0 if the monitor was successfully identified and removed.  Returns  a  non-
              zero value if the monitor could not be identified, which means it was either

                * never created for this resource

                * already cancelled

                * already triggered

                * just about to be triggered by a concurrent thread

              This function is thread-safe.

       int   enif_dynamic_resource_call(ErlNifEnv*   caller_env,       ERL_NIF_MODULE  rt_module,
       ERL_NIF_MODULE rt_name, ERL_NIF_TERM resource,      void* call_data)

              Call code of a resource type implemented by another NIF module. The atoms rt_module
              and rt_name identifies the resource type to be called. Argument resource identifies
              a resource object of that type.

              The callback dyncall of the identified resource type will be called with a  pointer
              to  the  resource  objects  obj  and  the  argument  call_data  passed through. The
              call_data argument is typically a pointer to a struct used to passed both arguments
              to the dyncall function as well as results back to the caller.

              Returns  0 if the dyncall callback function was called. Returns a non-zero value if
              no call was made, which happens  if  rt_module  and  rt_name  did  not  identify  a
              resource  type  with a dyncall callback or if resource was not a resource object of
              that type.

       int enif_equal_tids(ErlNifTid tid1, ErlNifTid tid2)

              Same as erl_drv_equal_tids.

       int enif_fprintf(FILE *stream, const char *format, ...)

              Similar to fprintf but this format string also accepts "%T", which  formats  Erlang
              terms of type ERL_NIF_TERM.

              This function is primarily intended for debugging purpose. It is not recommended to
              print very large terms with %T. The function may change errno, even if successful.

       void enif_free(void* ptr)

              Frees memory allocated by enif_alloc.

       void enif_free_env(ErlNifEnv* env)

              Frees an environment allocated  with  enif_alloc_env.  All  terms  created  in  the
              environment are freed as well.

       void enif_free_iovec(ErlNifIOVec* iov)

              Frees  an io vector returned from enif_inspect_iovec. This is needed only if a NULL
              environment is passed to enif_inspect_iovec.

              ErlNifIOVec *iovec = NULL;
              size_t max_elements = 128;
              ERL_NIF_TERM tail;
              if (!enif_inspect_iovec(NULL, max_elements, term, &tail, &iovec))
                return 0;

              // Do things with the iovec

              /* Free the iovector, possibly in another thread or nif function call */
              enif_free_iovec(iovec);

       int enif_get_atom(ErlNifEnv* env, ERL_NIF_TERM
               term, char* buf, unsigned size, ErlNifCharEncoding encode)

              Writes a NULL-terminated string in the buffer pointed  to  by  buf  of  size  size,
              consisting of the string representation of the atom term with encoding encode.

              Returns  the number of bytes written (including terminating NULL character) or 0 if
              term is not an atom with maximum length of size-1.

       int enif_get_atom_length(ErlNifEnv* env,
               ERL_NIF_TERM term, unsigned* len, ErlNifCharEncoding encode)

              Sets *len to the length (number of bytes excluding terminating NULL  character)  of
              the atom term with encoding encode.

              Returns true on success, or false if term is not an atom.

       int enif_get_double(ErlNifEnv* env,
               ERL_NIF_TERM term, double* dp)

              Sets *dp to the floating-point value of term.

              Returns true on success, or false if term is not a float.

       int enif_get_int(ErlNifEnv* env, ERL_NIF_TERM
               term, int* ip)

              Sets *ip to the integer value of term.

              Returns  true  on  success,  or  false  if term is not an integer or is outside the
              bounds of type int.

       int enif_get_int64(ErlNifEnv* env, ERL_NIF_TERM
               term, ErlNifSInt64* ip)

              Sets *ip to the integer value of term.

              Returns true on success, or false if term is not  an  integer  or  is  outside  the
              bounds of a signed 64-bit integer.

       int enif_get_local_pid(ErlNifEnv* env,
               ERL_NIF_TERM term, ErlNifPid* pid)

              If  term  is  the  pid  of  a node local process, this function initializes the pid
              variable *pid from it and returns true. Otherwise returns false. No check  is  done
              to see if the process is alive.

          Note:
              enif_get_local_pid will return false if argument term is the atom undefined.

       int enif_get_local_port(ErlNifEnv* env,
               ERL_NIF_TERM term, ErlNifPort* port_id)

              If  term  identifies a node local port, this function initializes the port variable
              *port_id from it and returns true. Otherwise returns false. No check is done to see
              if the port is alive.

       int enif_get_list_cell(ErlNifEnv* env,
               ERL_NIF_TERM list, ERL_NIF_TERM* head, ERL_NIF_TERM* tail)

              Sets *head and *tail from list list.

              Returns true on success, or false if it is not a list or the list is empty.

       int enif_get_list_length(ErlNifEnv* env,
               ERL_NIF_TERM term, unsigned* len)

              Sets *len to the length of list term.

              Returns true on success, or false if term is not a proper list.

       int enif_get_long(ErlNifEnv* env, ERL_NIF_TERM
               term, long int* ip)

              Sets *ip to the long integer value of term.

              Returns  true  on  success,  or  false  if term is not an integer or is outside the
              bounds of type long int.

       int enif_get_map_size(ErlNifEnv* env,
               ERL_NIF_TERM term, size_t *size)

              Sets *size to the number of key-value pairs in the map term.

              Returns true on success, or false if term is not a map.

       int enif_get_map_value(ErlNifEnv* env,
               ERL_NIF_TERM map, ERL_NIF_TERM key, ERL_NIF_TERM* value)

              Sets *value to the value associated with key in the map map.

              Returns true on success, or false if map is not a map or if map  does  not  contain
              key.

       int enif_get_resource(ErlNifEnv* env,
               ERL_NIF_TERM term, ErlNifResourceType* type, void** objp)

              Sets *objp to point to the resource object referred to by term.

              Returns  true  on success, or false if term is not a handle to a resource object of
              type type.

              enif_get_resource does not add a reference to the  resource  object.  However,  the
              pointer  received  in  *objp  is  guaranteed  to  be  valid at least as long as the
              resource handle term is valid.

       int enif_get_string(ErlNifEnv* env,
               ERL_NIF_TERM list, char* buf, unsigned size,
               ErlNifCharEncoding encode)

              Writes a NULL-terminated string in the buffer pointed to by  buf  with  size  size,
              consisting  of  the characters in the string list. The characters are written using
              encoding encode.

              Returns one of the following:

                * The number of bytes written (including terminating NULL character)

                * -size if the string was truncated because of buffer space

                * 0 if list is not a string that can be encoded with encode or if size was < 1.

              The written string is always NULL-terminated, unless buffer size is < 1.

       int enif_get_tuple(ErlNifEnv* env, ERL_NIF_TERM
               term, int* arity, const ERL_NIF_TERM** array)

              If term is a tuple, this function sets *array to point to an array  containing  the
              elements  of  the tuple, and sets *arity to the number of elements. Notice that the
              array is read-only and (*array)[N-1] is the Nth element of  the  tuple.  *array  is
              undefined if the arity of the tuple is zero.

              Returns true on success, or false if term is not a tuple.

       int enif_get_uint(ErlNifEnv* env, ERL_NIF_TERM
               term, unsigned int* ip)

              Sets *ip to the unsigned integer value of term.

              Returns  true on success, or false if term is not an unsigned integer or is outside
              the bounds of type unsigned int.

       int enif_get_uint64(ErlNifEnv* env,
               ERL_NIF_TERM term, ErlNifUInt64* ip)

              Sets *ip to the unsigned integer value of term.

              Returns true on success, or false if term is not an unsigned integer or is  outside
              the bounds of an unsigned 64-bit integer.

       int enif_get_ulong(ErlNifEnv* env, ERL_NIF_TERM
               term, unsigned long* ip)

              Sets *ip to the unsigned long integer value of term.

              Returns  true on success, or false if term is not an unsigned integer or is outside
              the bounds of type unsigned long.

       int enif_getenv(const char* key, char* value,
               size_t *value_size)

              Same as erl_drv_getenv.

       int enif_has_pending_exception(ErlNifEnv* env,
               ERL_NIF_TERM* reason)

              Returns true if a pending exception is associated  with  the  environment  env.  If
              reason  is  a NULL pointer, ignore it. Otherwise, if a pending exception associated
              with env exists, set *reason to the value of the exception term.  For  example,  if
              enif_make_badarg  is  called  to  set  a  pending badarg exception, a later call to
              enif_has_pending_exception(env, &reason) sets *reason  to  the  atom  badarg,  then
              return true.

              See also enif_make_badarg and enif_raise_exception.

       ErlNifUInt64 enif_hash(ErlNifHash type, ERL_NIF_TERM term, ErlNifUInt64 salt)

              Hashes term according to the specified ErlNifHash type.

              Ranges of taken salt (if any) and returned value depend on the hash type.

       int enif_inspect_binary(ErlNifEnv* env,
               ERL_NIF_TERM bin_term, ErlNifBinary* bin)

              Initializes  the  structure  pointed  to  by bin with information about binary term
              bin_term.

              Returns true on success, or false if bin_term is not a binary.

       int enif_inspect_iolist_as_binary(ErlNifEnv*
               env, ERL_NIF_TERM term, ErlNifBinary* bin)

              Initializes the structure pointed to by bin with a continuous buffer with the  same
              byte  content  as  iolist.  As  with  inspect_binary, the data pointed to by bin is
              transient and does not need to be released.

              Returns true on success, or false if iolist is not an iolist.

       int enif_inspect_iovec(ErlNifEnv*
               env, size_t max_elements, ERL_NIF_TERM iovec_term, ERL_NIF_TERM* tail,
               ErlNifIOVec** iovec)

              Fills iovec with the list  of  binaries  provided  in  iovec_term.  The  number  of
              elements  handled  in  the  call is limited to max_elements, and tail is set to the
              remainder of the list. Note that the output may be longer than max_elements on some
              platforms.

              To    create    a    list    of    binaries   from   an   arbitrary   iolist,   use
              erlang:iolist_to_iovec/1.

              When calling this function, iovec should contain a pointer to NULL or a ErlNifIOVec
              structure that should be used if possible. e.g.

              /* Don't use a pre-allocated structure */
              ErlNifIOVec *iovec = NULL;
              enif_inspect_iovec(env, max_elements, term, &tail, &iovec);

              /* Use a stack-allocated vector as an optimization for vectors with few elements */
              ErlNifIOVec vec, *iovec = &vec;
              enif_inspect_iovec(env, max_elements, term, &tail, &iovec);

              The  contents  of  the iovec is valid until the called nif function returns. If the
              iovec should be valid after the nif call returns,  it  is  possible  to  call  this
              function  with  a  NULL  environment. If no environment is given the iovec owns the
              data in the vector and it has to be explicitly freed using enif_free_iovec.

              Returns true on success, or false if iovec_term not an iovec.

       ErlNifIOQueue *enif_ioq_create(ErlNifIOQueueOpts opts)

              Create a new I/O Queue that can be used to store  data.  opts  has  to  be  set  to
              ERL_NIF_IOQ_NORMAL.

       void enif_ioq_destroy(ErlNifIOQueue *q)

              Destroy the I/O queue and free all of it's contents

       int enif_ioq_deq(ErlNifIOQueue *q, size_t count, size_t *size)

              Dequeue  count  bytes  from the I/O queue. If size is not NULL, the new size of the
              queue is placed there.

              Returns true on success, or false if the I/O  does  not  contain  count  bytes.  On
              failure the queue is left un-altered.

       int enif_ioq_enq_binary(ErlNifIOQueue *q, ErlNifBinary *bin, size_t skip)

              Enqueue the bin into q skipping the first skip bytes.

              Returns  true  on  success,  or  false if skip is greater than the size of bin. Any
              ownership of the binary data  is  transferred  to  the  queue  and  bin  is  to  be
              considered read-only for the rest of the NIF call and then as released.

       int enif_ioq_enqv(ErlNifIOQueue *q, ErlNifIOVec *iovec, size_t skip)

              Enqueue the iovec into q skipping the first skip bytes.

              Returns true on success, or false if skip is greater than the size of iovec.

       SysIOVec *enif_ioq_peek(ErlNifIOQueue *q, int *iovlen)

              Get the I/O queue as a pointer to an array of SysIOVecs. It also returns the number
              of elements in iovlen.

              Nothing is removed from the  queue  by  this  function,  that  must  be  done  with
              enif_ioq_deq.

              The returned array is suitable to use with the Unix system call writev.

       int  enif_ioq_peek_head(ErlNifEnv  *env,  ErlNifIOQueue  *q,  size_t  *size,  ERL_NIF_TERM
       *bin_term)

              Get the head of the IO Queue as a binary term.

              If size is not NULL, the size of the head is placed there.

              Nothing is removed from the  queue  by  this  function,  that  must  be  done  with
              enif_ioq_deq.

              Returns true on success, or false if the queue is empty.

       size_t enif_ioq_size(ErlNifIOQueue *q)

              Get the size of q.

       int enif_is_atom(ErlNifEnv* env, ERL_NIF_TERM term)

              Returns true if term is an atom.

       int enif_is_binary(ErlNifEnv* env, ERL_NIF_TERM term)

              Returns true if term is a binary.

       int enif_is_current_process_alive(ErlNifEnv* env)

              Returns  true  if  the  currently  executing  process is currently alive, otherwise
              false.

              This function can only be used from a NIF-calling thread, and with  an  environment
              corresponding to currently executing processes.

       int enif_is_empty_list(ErlNifEnv* env,
               ERL_NIF_TERM term)

              Returns true if term is an empty list.

       int enif_is_exception(ErlNifEnv* env,
               ERL_NIF_TERM term)

              Return true if term is an exception.

       int enif_is_fun(ErlNifEnv* env, ERL_NIF_TERM
               term)

              Returns true if term is a fun.

       int enif_is_identical(ERL_NIF_TERM lhs,
               ERL_NIF_TERM rhs)

              Returns  true  if  the two terms are identical. Corresponds to the Erlang operators
              =:= and =/=.

       int enif_is_list(ErlNifEnv* env, ERL_NIF_TERM term)

              Returns true if term is a list.

       int enif_is_map(ErlNifEnv* env, ERL_NIF_TERM
               term)

              Returns true if term is a map, otherwise false.

       int enif_is_number(ErlNifEnv* env, ERL_NIF_TERM
               term)

              Returns true if term is a number.

       int enif_is_pid(ErlNifEnv* env, ERL_NIF_TERM term)

              Returns true if term is a pid.

       int enif_is_pid_undefined(const ErlNifPid* pid)

              Returns true if pid has been set as undefined by enif_set_pid_undefined.

       int enif_is_port(ErlNifEnv* env, ERL_NIF_TERM term)

              Returns true if term is a port.

       int enif_is_port_alive(ErlNifEnv* env,
               ErlNifPort *port_id)

              Returns true if port_id is alive.

              This function is thread-safe.

       int enif_is_process_alive(ErlNifEnv* env,
               ErlNifPid *pid)

              Returns true if pid is alive.

              This function is thread-safe.

       int enif_is_ref(ErlNifEnv* env, ERL_NIF_TERM term)

              Returns true if term is a reference.

       int enif_is_tuple(ErlNifEnv* env, ERL_NIF_TERM term)

              Returns true if term is a tuple.

       int enif_keep_resource(void* obj)

              Adds a reference to resource object obj  obtained  from  enif_alloc_resource.  Each
              call   to  enif_keep_resource  for  an  object  must  be  balanced  by  a  call  to
              enif_release_resource before the object is destructed.

       ERL_NIF_TERM enif_make_atom(ErlNifEnv* env, const char* name)

              Creates an atom term from  the  NULL-terminated  C-string  name  with  ISO  Latin-1
              encoding. If the length of name exceeds the maximum length allowed for an atom (255
              characters), enif_make_atom invokes enif_make_badarg.

       ERL_NIF_TERM enif_make_atom_len(ErlNifEnv* env,
               const char* name, size_t len)

              Create an atom term from the string name  with  length  len.  NULL  characters  are
              treated  as  any other characters. If len exceeds the maximum length allowed for an
              atom (255 characters), enif_make_atom invokes enif_make_badarg.

       ERL_NIF_TERM enif_make_badarg(ErlNifEnv* env)

              Makes a badarg exception to  be  returned  from  a  NIF,  and  associates  it  with
              environment  env. Once a NIF or any function it calls invokes enif_make_badarg, the
              runtime ensures that a badarg exception is raised when the NIF returns, even if the
              NIF attempts to return a non-exception term instead.

              The  return  value  from enif_make_badarg can be used only as the return value from
              the NIF that invoked it (directly or indirectly) or be passed to enif_is_exception,
              but not to any other NIF API function.

              See also enif_has_pending_exception and enif_raise_exception.

          Note:
              Before  ERTS  7.0 (Erlang/OTP 18), the return value from enif_make_badarg had to be
              returned from the NIF. This requirement is now lifted as the return value from  the
              NIF is ignored if enif_make_badarg has been invoked.

       ERL_NIF_TERM enif_make_binary(ErlNifEnv* env, ErlNifBinary* bin)

              Makes  a  binary  term from bin. Any ownership of the binary data is transferred to
              the created term and bin is to be considered read-only for the rest of the NIF call
              and then as released.

       ERL_NIF_TERM enif_make_copy(ErlNifEnv* dst_env,
               ERL_NIF_TERM src_term)

              Makes  a  copy  of  term  src_term. The copy is created in environment dst_env. The
              source term can be located in any environment.

       ERL_NIF_TERM enif_make_double(ErlNifEnv* env, double d)

              Creates a floating-point term from a double. If argument double is not finite or is
              NaN, enif_make_double invokes enif_make_badarg.

       int enif_make_existing_atom(ErlNifEnv* env,
               const char* name, ERL_NIF_TERM* atom, ErlNifCharEncoding
               encode)

              Tries  to  create  the term of an already existing atom from the NULL-terminated C-
              string name with encoding encode.

              If the atom already exists, this function stores the  term  in  *atom  and  returns
              true, otherwise false. Also returns false if the length of name exceeds the maximum
              length allowed for an atom (255 characters).

       int enif_make_existing_atom_len(ErlNifEnv* env,
               const char* name, size_t len, ERL_NIF_TERM* atom, ErlNifCharEncoding
               encoding)

              Tries to create the term of an already existing atom  from  the  string  name  with
              length  len  and  encoding  encode.  NULL  characters  are  treated  as  any  other
              characters.

              If the atom already exists, this function stores the  term  in  *atom  and  returns
              true, otherwise false. Also returns false if len exceeds the maximum length allowed
              for an atom (255 characters).

       ERL_NIF_TERM enif_make_int(ErlNifEnv* env, int i)

              Creates an integer term.

       ERL_NIF_TERM enif_make_int64(ErlNifEnv* env, ErlNifSInt64 i)

              Creates an integer term from a signed 64-bit integer.

       ERL_NIF_TERM enif_make_list(ErlNifEnv* env, unsigned cnt, ...)

              Creates an ordinary list term of length cnt. Expects cnt number of arguments (after
              cnt) of type ERL_NIF_TERM as the elements of the list.

              Returns an empty list if cnt is 0.

       ERL_NIF_TERM enif_make_list1(ErlNifEnv* env, ERL_NIF_TERM e1)
       ERL_NIF_TERM enif_make_list2(ErlNifEnv* env,
               ERL_NIF_TERM e1, ERL_NIF_TERM e2)
       ERL_NIF_TERM enif_make_list3(ErlNifEnv* env,
               ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3)
       ERL_NIF_TERM enif_make_list4(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4)
       ERL_NIF_TERM enif_make_list5(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5)
       ERL_NIF_TERM enif_make_list6(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6)
       ERL_NIF_TERM enif_make_list7(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7)
       ERL_NIF_TERM enif_make_list8(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8)
       ERL_NIF_TERM enif_make_list9(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9)

              Creates  an  ordinary  list term with length indicated by the function name. Prefer
              these functions (macros) over the variadic enif_make_list  to  get  a  compile-time
              error if the number of arguments does not match.

       ERL_NIF_TERM enif_make_list_cell(ErlNifEnv*
               env, ERL_NIF_TERM head, ERL_NIF_TERM tail)

              Creates a list cell [head | tail].

       ERL_NIF_TERM enif_make_list_from_array(ErlNifEnv* env, const ERL_NIF_TERM
                 arr[], unsigned cnt)

              Creates an ordinary list containing the elements of array arr of length cnt.

              Returns an empty list if cnt is 0.

       ERL_NIF_TERM enif_make_long(ErlNifEnv* env, long int i)

              Creates an integer term from a long int.

       int enif_make_map_put(ErlNifEnv* env,
               ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM value,
               ERL_NIF_TERM* map_out)

              Makes  a  copy  of  map map_in and inserts key with value. If key already exists in
              map_in, the old associated value is replaced by value.

              If successful, this function sets *map_out to the new map and returns true. Returns
              false if map_in is not a map.

              The map_in term must belong to environment env.

       int enif_make_map_remove(ErlNifEnv* env,
               ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM* map_out)

              If  map  map_in contains key, this function makes a copy of map_in in *map_out, and
              removes key and the associated value. If map map_in does not contain key,  *map_out
              is set to map_in.

              Returns true on success, or false if map_in is not a map.

              The map_in term must belong to environment env.

       int enif_make_map_update(ErlNifEnv* env,
               ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM new_value,
               ERL_NIF_TERM* map_out)

              Makes  a  copy  of  map  map_in  and  replace the old associated value for key with
              new_value.

              If successful, this function sets *map_out to the new map and returns true. Returns
              false if map_in is not a map or if it does not contain key.

              The map_in term must belong to environment env.

       int enif_make_map_from_arrays(ErlNifEnv* env, ERL_NIF_TERM keys[],
               ERL_NIF_TERM values[], size_t cnt, ERL_NIF_TERM *map_out)

              Makes a map term from the given keys and values.

              If successful, this function sets *map_out to the new map and returns true. Returns
              false there are any duplicate keys.

              All keys and values must belong to env.

       ERL_NIF_TERM enif_make_monitor_term(ErlNifEnv* env, const ErlNifMonitor* mon)

              Creates a term identifying the given monitor received from enif_monitor_process.

              This function is primarily intended for debugging purpose.

       unsigned char *enif_make_new_binary(ErlNifEnv*
               env, size_t size, ERL_NIF_TERM* termp)

              Allocates a binary of size size bytes and creates an owning term. The  binary  data
              is  mutable  until  the  calling  NIF  returns. This is a quick way to create a new
              binary without having to use ErlNifBinary. The drawbacks are that the binary cannot
              be kept between NIF calls and it cannot be reallocated.

              Returns a pointer to the raw binary data and sets *termp to the binary term.

       ERL_NIF_TERM enif_make_new_map(ErlNifEnv* env)

              Makes an empty map term.

       ERL_NIF_TERM enif_make_pid(ErlNifEnv* env, const ErlNifPid* pid)

              Makes a pid term or the atom undefined from *pid.

       ERL_NIF_TERM enif_make_ref(ErlNifEnv* env)

              Creates a reference like erlang:make_ref/0.

       ERL_NIF_TERM enif_make_resource(ErlNifEnv* env, void* obj)

              Creates   an  opaque  handle  to  a  memory-managed  resource  object  obtained  by
              enif_alloc_resource. No ownership transfer is done, as the  resource  object  still
              needs  to  be  released  by enif_release_resource. However, notice that the call to
              enif_release_resource  can  occur  immediately  after  obtaining  the   term   from
              enif_make_resource,  in which case the resource object is deallocated when the term
              is garbage collected. For more details, see the example of creating and returning a
              resource object in the User's Guide.

          Note:
              Since ERTS 9.0 (OTP-20.0), resource terms have a defined behavior when compared and
              serialized through term_to_binary or passed between nodes.

                * Two resource terms will compare equal if and only if they would yield the  same
                  resource object pointer when passed to enif_get_resource.

                * A  resource  term  can  be  serialized  with  term_to_binary and later be fully
                  recreated if the resource object is still alive when binary_to_term is  called.
                  A  stale  resource  term  will  be returned from binary_to_term if the resource
                  object has been deallocated. enif_get_resource  will  return  false  for  stale
                  resource terms.

                  The  same  principles  of  serialization  apply  when passing resource terms in
                  messages to remote nodes and back again. A resource term will act stale on  all
                  nodes except the node where its resource object is still alive in memory.

              Before  ERTS 9.0 (OTP-20.0), all resource terms did compare equal to each other and
              to empty binaries (<<>>). If serialized, they would be  recreated  as  plain  empty
              binaries.

       ERL_NIF_TERM enif_make_resource_binary(ErlNifEnv* env, void* obj, const
               void* data, size_t size)

              Creates  a  binary term that is memory-managed by a resource object obj obtained by
              enif_alloc_resource. The returned binary term consists of size bytes pointed to  by
              data. This raw binary data must be kept readable and unchanged until the destructor
              of the resource is called. The binary data can be stored external to  the  resource
              object, in which case the destructor is responsible for releasing the data.

              Several  binary terms can be managed by the same resource object. The destructor is
              not called until the last binary is garbage collected. This can be useful to return
              different parts of a larger binary buffer.

              As with enif_make_resource, no ownership transfer is done. The resource still needs
              to be released with enif_release_resource.

       int enif_make_reverse_list(ErlNifEnv* env, ERL_NIF_TERM list_in,
               ERL_NIF_TERM *list_out)

              Sets *list_out to the reverse list of the list list_in and returns true, or returns
              false if list_in is not a list.

              This  function is only to be used on short lists, as a copy is created of the list,
              which is not released until after the NIF returns.

              The list_in term must belong to environment env.

       ERL_NIF_TERM enif_make_string(ErlNifEnv* env,
               const char* string, ErlNifCharEncoding encoding)

              Creates a list containing the characters of the NULL-terminated string string  with
              encoding encoding.

       ERL_NIF_TERM enif_make_string_len(ErlNifEnv*
               env, const char* string, size_t len, ErlNifCharEncoding
               encoding)

              Creates  a  list containing the characters of the string string with length len and
              encoding encoding. NULL characters are treated as any other characters.

       ERL_NIF_TERM enif_make_sub_binary(ErlNifEnv*
               env, ERL_NIF_TERM bin_term, size_t pos, size_t size)

              Makes a subbinary of binary bin_term, starting at zero-based position  pos  with  a
              length of size bytes. bin_term must be a binary or bitstring. pos+size must be less
              or equal to the number of whole bytes in bin_term.

       ERL_NIF_TERM enif_make_tuple(ErlNifEnv* env,
               unsigned cnt, ...)

              Creates a tuple term of arity cnt. Expects cnt number of arguments (after  cnt)  of
              type ERL_NIF_TERM as the elements of the tuple.

       ERL_NIF_TERM enif_make_tuple1(ErlNifEnv* env,
               ERL_NIF_TERM e1)
       ERL_NIF_TERM enif_make_tuple2(ErlNifEnv* env,
               ERL_NIF_TERM e1, ERL_NIF_TERM e2)
       ERL_NIF_TERM enif_make_tuple3(ErlNifEnv* env,
               ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3)
       ERL_NIF_TERM enif_make_tuple4(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4)
       ERL_NIF_TERM enif_make_tuple5(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5)
       ERL_NIF_TERM enif_make_tuple6(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6)
       ERL_NIF_TERM enif_make_tuple7(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7)
       ERL_NIF_TERM enif_make_tuple8(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8)
       ERL_NIF_TERM enif_make_tuple9(ErlNifEnv* env,
               ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9)

              Creates  a  tuple  term  with  length  indicated by the function name. Prefer these
              functions (macros) over the variadic enif_make_tuple to get a compile-time error if
              the number of arguments does not match.

       ERL_NIF_TERM enif_make_tuple_from_array(ErlNifEnv* env, const ERL_NIF_TERM
               arr[], unsigned cnt)

              Creates a tuple containing the elements of array arr of length cnt.

       ERL_NIF_TERM enif_make_uint(ErlNifEnv* env, unsigned int i)

              Creates an integer term from an unsigned int.

       ERL_NIF_TERM enif_make_uint64(ErlNifEnv* env, ErlNifUInt64 i)

              Creates an integer term from an unsigned 64-bit integer.

       ERL_NIF_TERM enif_make_ulong(ErlNifEnv* env, unsigned long i)

              Creates an integer term from an unsigned long int.

       ERL_NIF_TERM enif_make_unique_integer(ErlNifEnv
               *env, ErlNifUniqueInteger properties)

              Returns   a   unique   integer   with   the   same   properties   as  specified  by
              erlang:unique_integer/1.

              env is the environment to create the integer in.

              ERL_NIF_UNIQUE_POSITIVE and ERL_NIF_UNIQUE_MONOTONIC can be passed  as  the  second
              argument  to change the properties of the integer returned. They can be combined by
              OR:ing the two values together.

              See also ErlNifUniqueInteger.

       int enif_map_iterator_create(ErlNifEnv *env,
               ERL_NIF_TERM map, ErlNifMapIterator *iter, ErlNifMapIteratorEntry
               entry)

              Creates an iterator for the map map by initializing the  structure  pointed  to  by
              iter.   Argument   entry   determines   the   start   position   of  the  iterator:
              ERL_NIF_MAP_ITERATOR_FIRST or ERL_NIF_MAP_ITERATOR_LAST.

              Returns true on success, or false if map is not a map.

              A map iterator is only useful during the lifetime of environment env that  the  map
              belongs to. The iterator must be destroyed by calling enif_map_iterator_destroy:

              ERL_NIF_TERM key, value;
              ErlNifMapIterator iter;
              enif_map_iterator_create(env, my_map, &iter, ERL_NIF_MAP_ITERATOR_FIRST);

              while (enif_map_iterator_get_pair(env, &iter, &key, &value)) {
                  do_something(key,value);
                  enif_map_iterator_next(env, &iter);
              }
              enif_map_iterator_destroy(env, &iter);

          Note:
              The key-value pairs of a map have no defined iteration order. The only guarantee is
              that the iteration order of a single map instance is preserved during the  lifetime
              of the environment that the map belongs to.

       void enif_map_iterator_destroy(ErlNifEnv *env,
               ErlNifMapIterator *iter)

              Destroys a map iterator created by enif_map_iterator_create.

       int enif_map_iterator_get_pair(ErlNifEnv *env,
               ErlNifMapIterator *iter, ERL_NIF_TERM *key, ERL_NIF_TERM
               *value)

              Gets key and value terms at the current map iterator position.

              On success, sets *key and *value and returns true. Returns false if the iterator is
              positioned at head (before first entry) or tail (beyond last entry).

       int enif_map_iterator_is_head(ErlNifEnv *env,
               ErlNifMapIterator *iter)

              Returns true if map iterator iter is positioned before the first entry.

       int enif_map_iterator_is_tail(ErlNifEnv *env,
               ErlNifMapIterator *iter)

              Returns true if map iterator iter is positioned after the last entry.

       int enif_map_iterator_next(ErlNifEnv *env,
               ErlNifMapIterator *iter)

              Increments map iterator to point to the next key-value entry.

              Returns true if the iterator is now positioned at a valid key-value entry, or false
              if the iterator is positioned at the tail (beyond the last entry).

       int enif_map_iterator_prev(ErlNifEnv *env,
               ErlNifMapIterator *iter)

              Decrements map iterator to point to the previous key-value entry.

              Returns true if the iterator is now positioned at a valid key-value entry, or false
              if the iterator is positioned at the head (before the first entry).

       int enif_monitor_process(ErlNifEnv* caller_env,
             void* obj, const ErlNifPid* target_pid, ErlNifMonitor* mon)

              Starts monitoring a process from a resource. When a process is monitored, a process
              exit  results  in a call to the provided down callback associated with the resource
              type.

              Argument obj is pointer to  the  resource  to  hold  the  monitor  and  *target_pid
              identifies the local process to be monitored.

              If  mon  is  not  NULL, a successful call stores the identity of the monitor in the
              ErlNifMonitor struct pointed to by mon. This identifier is used  to  refer  to  the
              monitor   for   later   removal   with   enif_demonitor_process   or  compare  with
              enif_compare_monitors. A monitor is automatically removed when it triggers or  when
              the resource is deallocated.

              Argument  caller_env  is  the  environment  of the calling thread (process bound or
              callback environment) or NULL if calling from a custom thread not spawned by ERTS.

              Returns 0 on success, < 0 if no down callback is provided, and > 0 if  the  process
              is no longer alive or if target_pid is  undefined.

              This function is thread-safe.

       ErlNifTime enif_monotonic_time(ErlNifTimeUnit time_unit)

              Returns  the  current   Erlang  monotonic time. Notice that it is not uncommon with
              negative values.

              time_unit is the time unit of the returned value.

              Returns ERL_NIF_TIME_ERROR if called with an invalid  time  unit  argument,  or  if
              called from a thread that is not a scheduler thread.

              See also ErlNifTime and ErlNifTimeUnit.

       ErlNifMutex *enif_mutex_create(char *name)

              Same as erl_drv_mutex_create.

       void enif_mutex_destroy(ErlNifMutex *mtx)

              Same as erl_drv_mutex_destroy.

       void enif_mutex_lock(ErlNifMutex *mtx)

              Same as erl_drv_mutex_lock.

       char*enif_mutex_name(ErlNifMutex* mtx)

              Same as erl_drv_mutex_name.

       int enif_mutex_trylock(ErlNifMutex *mtx)

              Same as erl_drv_mutex_trylock.

       void enif_mutex_unlock(ErlNifMutex *mtx)

              Same as erl_drv_mutex_unlock.

       ERL_NIF_TERM enif_now_time(ErlNifEnv *env)

              Returns an erlang:now() time stamp.

              This function is deprecated.

       ErlNifResourceType *enif_open_resource_type(ErlNifEnv* env, const char*
               module_str, const char* name, ErlNifResourceDtor* dtor,
               ErlNifResourceFlags flags, ErlNifResourceFlags* tried)

              Creates  or  takes  over a resource type identified by the string name and gives it
              the destructor function pointed to by dtor. Argument flags can have  the  following
              values:

                ERL_NIF_RT_CREATE:
                  Creates a new resource type that does not already exist.

                ERL_NIF_RT_TAKEOVER:
                  Opens  an existing resource type and takes over ownership of all its instances.
                  The supplied destructor dtor is called both  for  existing  instances  and  new
                  instances not yet created by the calling NIF library.

              The  two  flag  values  can  be combined with bitwise OR. The resource type name is
              local to the calling module. Argument module_str is not  (yet)  used  and  must  be
              NULL. dtor can be NULL if no destructor is needed.

              On  success,  the function returns a pointer to the resource type and *tried is set
              to either ERL_NIF_RT_CREATE or ERL_NIF_RT_TAKEOVER to indicate what  was  done.  On
              failure, returns NULL and sets *tried to flags. It is allowed to set tried to NULL.

              Notice  that  enif_open_resource_type  is  only  allowed  to  be  called in the two
              callbacks load and upgrade.

              See also enif_open_resource_type_x.

       ErlNifResourceType *enif_open_resource_type_x(ErlNifEnv* env, const char* name,      const
       ErlNifResourceTypeInit* init,
               ErlNifResourceFlags flags, ErlNifResourceFlags* tried)

              Same as enif_open_resource_type except it accepts additional callback functions for
              resource types that are used together with enif_select and enif_monitor_process.

              Argument init is a pointer to an ErlNifResourceTypeInit structure that contains the
              function pointers for destructor, down and stop callbacks for the resource type.

          Note:
              Only   members   dtor,   down  and  stop  in  ErlNifResourceTypeInit  are  read  by
              enif_open_resource_type_x.   To   implement   the   new   dyncall   callback    use
              enif_init_resource_type.

       ErlNifResourceType  *enif_init_resource_type(ErlNifEnv*  env, const char* name,      const
       ErlNifResourceTypeInit* init,
               ErlNifResourceFlags flags, ErlNifResourceFlags* tried)

              Same as enif_open_resource_type_x except it accepts an additional callback function
              for resource types that are used together with enif_dynamic_resource_call.

              Argument init is a pointer to an ErlNifResourceTypeInit structure that contains the
              callback function pointers dtor, down, stop and the new dyncall.  The  struct  also
              contains  the field members that must be set to the number of initialized callbacks
              counted from the top of the  struct.  For  example,  to  initialize  all  callbacks
              including  dyncall,  members should be set to 4. All callbacks are optional and may
              be set to NULL.

       int enif_port_command(ErlNifEnv* env, const
              ErlNifPort* to_port, ErlNifEnv *msg_env, ERL_NIF_TERM msg)

              Works as erlang:port_command/2, except that it is always completely asynchronous.

                env:
                  The environment of the calling process. Must not be NULL.

                *to_port:
                  The port ID of the receiving port. The port ID is to refer to  a  port  on  the
                  local node.

                msg_env:
                  The  environment  of the message term. Can be a process independent environment
                  allocated with enif_alloc_env or NULL.

                msg:
                  The message term to send. The same limitations  apply  as  on  the  payload  to
                  erlang:port_command/2.

              Using  a  msg_env  of  NULL  is  an  optimization,  which  groups together calls to
              enif_alloc_env, enif_make_copy, enif_port_command, and enif_free_env into one call.
              This optimization is only useful when a majority of the terms are to be copied from
              env to msg_env.

              Returns true if the command is successfully sent.  Returns  false  if  the  command
              fails, for example:

                * *to_port does not refer to a local port.

                * The currently executing process (that is, the sender) is not alive.

                * msg is invalid.

              See also enif_get_local_port.

       void *enif_priv_data(ErlNifEnv* env)

              Returns the pointer to the private data that was set by load or upgrade.

       ERL_NIF_TERM enif_raise_exception(ErlNifEnv*
               env, ERL_NIF_TERM reason)

              Creates  an  error  exception  with  the term reason to be returned from a NIF, and
              associates it with environment env. Once a NIF or any  function  it  calls  invokes
              enif_raise_exception,  the  runtime ensures that the exception it creates is raised
              when the NIF returns, even if the NIF  attempts  to  return  a  non-exception  term
              instead.

              The  return  value  from  enif_raise_exception can only be used as the return value
              from  the  NIF  that  invoked  it  (directly  or  indirectly)  or  be   passed   to
              enif_is_exception, but not to any other NIF API function.

              See also enif_has_pending_exception and enif_make_badarg.

       void *enif_realloc(void* ptr, size_t size)

              Reallocates memory allocated by enif_alloc to size bytes.

              Returns NULL if the reallocation fails.

              The  returned  pointer  is  suitably  aligned for any built-in type that fit in the
              allocated memory.

       int enif_realloc_binary(ErlNifBinary* bin, size_t size)

              Changes the size of a binary bin. The source binary can be read-only, in which case
              it is left untouched and a mutable copy is allocated and assigned to *bin.

              Returns true on success, or false if memory allocation failed.

       void enif_release_binary(ErlNifBinary* bin)

              Releases a binary obtained from enif_alloc_binary.

       void enif_release_resource(void* obj)

              Removes  a  reference to resource object obj obtained from enif_alloc_resource. The
              resource object is destructed when the last reference  is  removed.  Each  call  to
              enif_release_resource  must correspond to a previous call to enif_alloc_resource or
              enif_keep_resource. References made by enif_make_resource can only  be  removed  by
              the garbage collector.

              There  are no guarantees exactly when the destructor of an unreferenced resource is
              called. It could be called directly by enif_release_resource but it could  also  be
              scheduled to be called at a later time possibly by another thread.

       ErlNifRWLock *enif_rwlock_create(char *name)

              Same as erl_drv_rwlock_create.

       void enif_rwlock_destroy(ErlNifRWLock *rwlck)

              Same as erl_drv_rwlock_destroy.

       char*enif_rwlock_name(ErlNifRWLock* rwlck)

              Same as erl_drv_rwlock_name.

       void enif_rwlock_rlock(ErlNifRWLock *rwlck)

              Same as erl_drv_rwlock_rlock.

       void enif_rwlock_runlock(ErlNifRWLock *rwlck)

              Same as erl_drv_rwlock_runlock.

       void enif_rwlock_rwlock(ErlNifRWLock *rwlck)

              Same as erl_drv_rwlock_rwlock.

       void enif_rwlock_rwunlock(ErlNifRWLock *rwlck)

              Same as erl_drv_rwlock_rwunlock.

       int enif_rwlock_tryrlock(ErlNifRWLock *rwlck)

              Same as erl_drv_rwlock_tryrlock.

       int enif_rwlock_tryrwlock(ErlNifRWLock *rwlck)

              Same as erl_drv_rwlock_tryrwlock.

       ERL_NIF_TERM enif_schedule_nif(
               ErlNifEnv*   caller_env,   const  char*  fun_name,  int  flags,       ERL_NIF_TERM
       (*fp)(ErlNifEnv*  env,  int  argc,  const  ERL_NIF_TERM  argv[]),       int  argc,   const
       ERL_NIF_TERM argv[])

              Schedules  NIF fp to execute. This function allows an application to break up long-
              running work into multiple regular NIF calls or to schedule a  dirty NIF to execute
              on a dirty scheduler thread.

                caller_env:
                  Must be process bound environment of the calling NIF.

                fun_name:
                  Provides  a  name  for the NIF that is scheduled for execution. If it cannot be
                  converted to an atom, enif_schedule_nif returns a badarg exception.

                flags:
                  Must be set to 0 for a regular NIF.  If  the  emulator  was  built  with  dirty
                  scheduler     support     enabled,    flags    can    be    set    to    either
                  ERL_NIF_DIRTY_JOB_CPU_BOUND  if  the  job  is  expected  to  be  CPU-bound,  or
                  ERL_NIF_DIRTY_JOB_IO_BOUND  for jobs that will be I/O-bound. If dirty scheduler
                  threads are not available in the emulator, an attempt to schedule  such  a  job
                  results in a notsup exception.

                argc and argv:
                  Can  either  be  the  originals  passed  into the calling NIF, or can be values
                  created by the calling NIF.

              The calling NIF must use the return value of enif_schedule_nif as  its  own  return
              value.

              Be  aware  that  enif_schedule_nif, as its name implies, only schedules the NIF for
              future execution. The calling NIF does not block waiting for the scheduled  NIF  to
              execute  and  return.  This means that the calling NIF cannot expect to receive the
              scheduled NIF return value and use it for further operations.

       int enif_select(ErlNifEnv* env, ErlNifEvent event, enum ErlNifSelectFlags mode,      void*
       obj, const ErlNifPid* pid, ERL_NIF_TERM ref)

              This  function  can  be used to receive asynchronous notifications when OS-specific
              event objects become ready for either read or write operations.

              Argument event  identifies  the  event  object.  On  Unix  systems,  the  functions
              select/poll  are  used.  The  event  object  must  be  a socket, pipe or other file
              descriptor object that select/poll can use.

              Argument  mode  describes  the  type  of  events   to   wait   for.   It   can   be
              ERL_NIF_SELECT_READ,  ERL_NIF_SELECT_WRITE  or a bitwise OR combination to wait for
              both. It  can  also  be  ERL_NIF_SELECT_STOP  or  ERL_NIF_SELECT_CANCEL  which  are
              described  further  below.  When a read or write event is triggered, a notification
              message like this is sent to the process identified by pid:

              {select, Obj, Ref, ready_input | ready_output}

              ready_input or ready_output indicates if the event object is ready for  reading  or
              writing.

          Note:
              For   complete   control   over   the   message  format  use  the  newer  functions
              enif_select_read or enif_select_write introduced in erts-11.0 (OTP-22.0).

              Argument pid may be NULL to indicate the calling process. It must  not  be  set  as
              undefined.

              Argument obj is a resource object obtained from enif_alloc_resource. The purpose of
              the resource objects is as a container of the event object to manage its state  and
              lifetime. A handle to the resource is received in the notification message as Obj.

              Argument ref must be either a reference obtained from erlang:make_ref/0 or the atom
              undefined. It will be passed as Ref in the notifications. If  a  selective  receive
              statement is used to wait for the notification then a reference created just before
              the receive will exploit a runtime optimization that bypasses all earlier  received
              messages in the queue.

              The  notifications  are one-shot only. To receive further notifications of the same
              type (read or write), repeated calls to enif_select must be  made  after  receiving
              each notification.

              ERL_NIF_SELECT_CANCEL  can be used to cancel previously selected events. It must be
              used   in   a   bitwise   OR   combination    with    ERL_NIF_SELECT_READ    and/or
              ERL_NIF_SELECT_WRITE  to  indicate which type of event to cancel. Arguments pid and
              ref are ignored when ERL_NIF_SELECT_CANCEL is specified. The return value will tell
              if  the  event  was  actually  cancelled or if a notification may already have been
              sent.

              Use ERL_NIF_SELECT_STOP as mode in order to safely close an event object  that  has
              been  passed  to  enif_select. The stop callback of the resource obj will be called
              when it is safe to close the event object. This safe way of closing  event  objects
              must  be  used  even  if all notifications have been received (or cancelled) and no
              further calls to enif_select have been made. ERL_NIF_SELECT_STOP will first  cancel
              any  selected  events before it calls or schedules the stop callback. Arguments pid
              and ref are ignored when ERL_NIF_SELECT_STOP is specified.

              The first call to enif_select for a specific OS event  will  establish  a  relation
              between  the  event object and the containing resource. All subsequent calls for an
              event must pass its containing resource as argument obj. The relation is  dissolved
              when  enif_select  has  been  called  with  mode  as  ERL_NIF_SELECT_STOP  and  the
              corresponding stop callback has returned. A  resource  can  contain  several  event
              objects  but one event object can only be contained within one resource. A resource
              will not be destructed until all its contained relations have been dissolved.

          Note:
              Use  enif_monitor_process  together  with  enif_select  to  detect  failing  Erlang
              processes  and  prevent  them from causing permanent leakage of resources and their
              contained OS event objects.

              Returns a non-negative value on success where the following bits can be set:

                ERL_NIF_SELECT_STOP_CALLED:
                  The stop callback was called directly by enif_select.

                ERL_NIF_SELECT_STOP_SCHEDULED:
                  The stop callback was scheduled to run on some other thread or  later  by  this
                  thread.

                ERL_NIF_SELECT_READ_CANCELLED:
                  A  read event was cancelled by ERL_NIF_SELECT_CANCEL or ERL_NIF_SELECT_STOP and
                  is guaranteed not to generate a ready_input notification message.

                ERL_NIF_SELECT_WRITE_CANCELLED:
                  A write event was cancelled by ERL_NIF_SELECT_CANCEL or ERL_NIF_SELECT_STOP and
                  is guaranteed not to generate a ready_output notification message.

              Returns a negative value if the call failed where the following bits can be set:

                ERL_NIF_SELECT_INVALID_EVENT:
                  Argument event is not a valid OS event object.

                ERL_NIF_SELECT_FAILED:
                  The system call failed to add the event object to the poll set.

          Note:
              Use bitwise AND to test for specific bits in the return value. New significant bits
              may be added in future releases to give more detailed information for  both  failed
              and  successful  calls.  Do  NOT use equality tests like ==, as that may cause your
              application to stop working.

              Example:

              retval = enif_select(env, fd, ERL_NIF_SELECT_STOP, resource, ref);
              if (retval < 0) {
                  /* handle error */
              }
              /* Success! */
              if (retval & ERL_NIF_SELECT_STOP_CALLED) {
                  /* ... */
              }

          Note:
              The    mode     flag     ERL_NIF_SELECT_CANCEL     and     the     return     flags
              ERL_NIF_SELECT_READ_CANCELLED and ERL_NIF_SELECT_WRITE_CANCELLED were introduced in
              erts-11.0 (OTP-22.0).

       int enif_select_read(ErlNifEnv* env, ErlNifEvent event, void* obj,
             const ErlNifPid* pid, ERL_NIF_TERM msg, ErlNifEnv* msg_env)
       int enif_select_write(ErlNifEnv* env, ErlNifEvent event, void* obj,
             const ErlNifPid* pid, ERL_NIF_TERM msg, ErlNifEnv* msg_env)

              These are variants of enif_select where you can supply your own  message  term  msg
              that will be sent to the process instead of the predefined tuple {select,_,_,_}.

              Argument  msg_env  must  either  be  NULL  or the environment of msg allocated with
              enif_alloc_env. If argument msg_env is NULL the term msg will be copied,  otherwise
              both  msg  and msg_env will be invalidated by a successful call to enif_select_read
              or enif_select_write. The environment is then to either be freed with enif_free_env
              or  cleared  for reuse with enif_clear_env. An unsuccessful call will leave msg and
              msg_env still valid.

              Apart from  the  message  format  enif_select_read  and  enif_select_write  behaves
              exactly the same as enif_select with argument mode as either ERL_NIF_SELECT_READ or
              ERL_NIF_SELECT_WRITE. To cancel or close events use enif_select.

       ErlNifPid *enif_self(ErlNifEnv* caller_env, ErlNifPid* pid)

              Initializes the ErlNifPid variable at *pid to represent the calling process.

              Returns  pid  if  successful,  or  NULL  if  caller_env  is  not  a  process  bound
              environment.

       int enif_send(ErlNifEnv* caller_env,
             ErlNifPid* to_pid, ErlNifEnv* msg_env, ERL_NIF_TERM msg)

              Sends a message to a process.

                caller_env:
                   The  environment of the calling thread (process bound or callback environment)
                  or NULL if calling from a custom thread not spawned by ERTS.

                *to_pid:
                  The pid of the receiving process. The pid is to refer to a process on the local
                  node.

                msg_env:
                  The  environment of the message term. Must be a process independent environment
                  allocated with enif_alloc_env or NULL.

                msg:
                  The message term to send.

              Returns true if the message  is  successfully  sent.  Returns  false  if  the  send
              operation fails, that is:

                * *to_pid does not refer to an alive local process.

                * The currently executing process (that is, the sender) is not alive.

              The  message  environment msg_env with all its terms (including msg) is invalidated
              by a successful call to enif_send. The environment  is  to  either  be  freed  with
              enif_free_env  or  cleared for reuse with enif_clear_env. An unsuccessful call will
              leave msg and msg_env still valid.

              If msg_env is set to NULL, the msg term is copied and the  original  term  and  its
              environment is still valid after the call.

              This function is thread-safe.

          Note:
              Passing msg_env as NULL is only supported as from ERTS 8.0 (Erlang/OTP 19).

       void enif_set_pid_undefined(ErlNifPid* pid)

              Sets an ErlNifPid variable as undefined. See enif_is_pid_undefined.

       unsigned enif_sizeof_resource(void* obj)

              Gets the byte size of resource object obj obtained by enif_alloc_resource.

       int enif_snprintf(char *str, size_t size, const
               char *format, ...)

              Similar  to snprintf but this format string also accepts "%T", which formats Erlang
              terms of type ERL_NIF_TERM.

              This function is primarily intended for debugging purpose. It is not recommended to
              print very large terms with %T. The function may change errno, even if successful.

       void enif_system_info(ErlNifSysInfo
               *sys_info_ptr, size_t size)

              Same as driver_system_info.

       int enif_term_to_binary(ErlNifEnv *env,
               ERL_NIF_TERM term, ErlNifBinary *bin)

              Allocates  a  new  binary  with enif_alloc_binary and stores the result of encoding
              term according to the Erlang external term format.

              Returns true on success, or false if the allocation fails.

              See also erlang:term_to_binary/1 and enif_binary_to_term.

       ErlNifTermType enif_term_type(ErlNifEnv *env, ERL_NIF_TERM term)

              Determines the type of the given term. The term must be an ordinary Erlang term and
              not  one  of the special terms returned by enif_raise_exception, enif_schedule_nif,
              or similar.

              The following types are defined at the moment:

                ERL_NIF_TERM_TYPE_ATOM:

                ERL_NIF_TERM_TYPE_BITSTRING:
                  A bitstring or binary

                ERL_NIF_TERM_TYPE_FLOAT:

                ERL_NIF_TERM_TYPE_FUN:

                ERL_NIF_TERM_TYPE_INTEGER:

                ERL_NIF_TERM_TYPE_LIST:
                  A list, empty or not

                ERL_NIF_TERM_TYPE_MAP:

                ERL_NIF_TERM_TYPE_PID:

                ERL_NIF_TERM_TYPE_PORT:

                ERL_NIF_TERM_TYPE_REFERENCE:

                ERL_NIF_TERM_TYPE_TUPLE:

              Note that new types may be added in the future, so the caller must be  prepared  to
              handle unknown types.

       int enif_thread_create(char *name,ErlNifTid
               *tid,void * (*func)(void *),void *args,ErlNifThreadOpts
               *opts)

              Same as erl_drv_thread_create.

       void enif_thread_exit(void *resp)

              Same as erl_drv_thread_exit.

       int enif_thread_join(ErlNifTid, void **respp)

              Same as erl_drv_thread_join.

       char*enif_thread_name(ErlNifTid tid)

              Same as erl_drv_thread_name.

       ErlNifThreadOpts *enif_thread_opts_create(char *name)

              Same as erl_drv_thread_opts_create.

       void enif_thread_opts_destroy(ErlNifThreadOpts *opts)

              Same as erl_drv_thread_opts_destroy.

       ErlNifTid enif_thread_self(void)

              Same as erl_drv_thread_self.

       int enif_thread_type(void)

              Determine  the  type  of  currently  executing thread. A positive value indicates a
              scheduler thread while a negative value or zero indicates another type  of  thread.
              Currently the following specific types exist (which may be extended in the future):

                ERL_NIF_THR_UNDEFINED:
                  Undefined thread that is not a scheduler thread.

                ERL_NIF_THR_NORMAL_SCHEDULER:
                  A normal scheduler thread.

                ERL_NIF_THR_DIRTY_CPU_SCHEDULER:
                  A dirty CPU scheduler thread.

                ERL_NIF_THR_DIRTY_IO_SCHEDULER:
                  A dirty I/O scheduler thread.

       ErlNifTime enif_time_offset(ErlNifTimeUnit time_unit)

              Returns  the  current time offset between  Erlang monotonic time and  Erlang system
              time converted into the time_unit passed as argument.

              time_unit is the time unit of the returned value.

              Returns ERL_NIF_TIME_ERROR if called with an  invalid  time  unit  argument  or  if
              called from a thread that is not a scheduler thread.

              See also ErlNifTime and ErlNifTimeUnit.

       void *enif_tsd_get(ErlNifTSDKey key)

              Same as erl_drv_tsd_get.

       int enif_tsd_key_create(char *name, ErlNifTSDKey *key)

              Same as erl_drv_tsd_key_create.

       void enif_tsd_key_destroy(ErlNifTSDKey key)

              Same as erl_drv_tsd_key_destroy.

       void enif_tsd_set(ErlNifTSDKey key, void *data)

              Same as erl_drv_tsd_set.

       int enif_vfprintf(FILE *stream, const char *format, va_list ap)

              Equivalent  to  enif_fprintf  except  that  its  called with a va_list instead of a
              variable number of arguments.

       int enif_vsnprintf(char *str, size_t size, const char *format, va_list ap)

              Equivalent to enif_snprintf except that its called with  a  va_list  instead  of  a
              variable number of arguments.

       int enif_whereis_pid(ErlNifEnv *caller_env,
                 ERL_NIF_TERM name, ErlNifPid *pid)

              Looks up a process by its registered name.

                caller_env:
                  The  environment  of the calling thread (process bound or callback environment)
                  or NULL if calling from a custom thread not spawned by ERTS.

                name:
                  The name of a registered process, as an atom.

                *pid:
                  The ErlNifPid in which the resolved process id is stored.

              On success, sets *pid to the local process registered with name and  returns  true.
              If  name is not a registered process, or is not an atom, false is returned and *pid
              is unchanged.

              Works as erlang:whereis/1, but restricted to processes.  See  enif_whereis_port  to
              resolve registered ports.

       int enif_whereis_port(ErlNifEnv *caller_env,
                 ERL_NIF_TERM name, ErlNifPort *port)

              Looks up a port by its registered name.

                caller_env:
                  The  environment  of the calling thread (process bound or callback environment)
                  or NULL if calling from a custom thread not spawned by ERTS.

                name:
                  The name of a registered port, as an atom.

                *port:
                  The ErlNifPort in which the resolved port id is stored.

              On success, sets *port to the port registered with name and returns true.  If  name
              is  not  a  registered  port,  or  is  not  an atom, false is returned and *port is
              unchanged.

              Works as erlang:whereis/1, but restricted to ports. See enif_whereis_pid to resolve
              registered processes.

SEE ALSO

       erlang:load_nif/2
       NIFs (tutorial)
       Debugging NIFs and Port Drivers