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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]).

       -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.

       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.

   Warning:
       There  is a known limitation for Erlang fallback functions of NIFs. Avoid functions involved in traversal
       of binaries by matching and recursion. If a NIF is loaded over such function, binary arguments to the NIF
       may get corrupted and cause VM crash or other misbehavior.

       Example of such bad fallback function:

       skip_until(Byte, <<Byte, Rest/binary>>) ->
           Rest;
       skip_until(Byte, <<_, Rest/binary>>) ->
           skip_until(Byte, Rest).

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   for   static  inclusion  through  --enable-static-nifs,  you  must  define
           STATIC_ERLANG_NIF before the ERL_NIF_INIT declaration.

         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 actualy 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