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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. Each NIF must also have an implementation in Erlang that will be
       invoked if the function is called before the NIF library has been successfully  loaded.  A
       typical  such  stub  implementation is to throw an exception. But it can also be used as a
       fallback implementation if the NIF library is not implemented for some architecture.

   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 can not provide the same services as
       provided when executing Erlang code, such as preemptive scheduling or  memory  protection.
       If the native function doesn't behave well, the whole VM will misbehave.

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

         * An   erroneously   implemented  native  function  might  cause  a  VM  internal  state
           inconsistency which may 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 that do lengthy work before returning will degrade responsiveness of
           the VM, and may 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 might occur due  to  lengthy  work  may  also  vary
           between OTP releases.

       The  NIF  concept  is  officially supported from R14B. NIF source code written for earlier
       experimental versions might need adaption to run on R14B or later versions:

         * No incompatible changes between R14B and R14A.

         * Incompatible changes between R14A and R13B04:

           * Environment   argument   removed   for    enif_alloc,    enif_realloc,    enif_free,
             enif_alloc_binary,  enif_realloc_binary,  enif_release_binary,  enif_alloc_resource,
             enif_release_resource, enif_is_identical and enif_compare.

           * Character encoding argument added to enif_get_atom and enif_make_existing_atom.

           * Module argument added to  enif_open_resource_type  while  changing  name  spaces  of
             resource types from global to module local.

         * Incompatible changes between R13B04 and R13B03:

           * The  function prototypes of the NIFs have changed to expect argc and argv arguments.
             The arity of a NIF is by that no longer limited to 3.

           * enif_get_data renamed as enif_priv_data.

           * enif_make_string got a third argument for character encoding.

       A minimal example of a NIF library can look like this:

       /* 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)

       and the Erlang module would have to look something like this:

       -module(niftest).

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

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

       hello() ->
             "NIF library not loaded".

       and compile and test something like this (on Linux):

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

       1> c(niftest).
       {ok,niftest}
       2> niftest:hello().
       "NIF library not loaded"
       3> niftest:init().
       ok
       4> niftest:hello().
       "Hello world!"

       A better solution for a real module is to take advantage of the new directive  on_load  to
       automatically load the NIF library when the module is loaded.

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

       A  loaded  NIF  library  is  tied to the Erlang module code version that loaded it. If the
       module is upgraded with a new version, the new Erlang code will have to load its  own  NIF
       library  (or  maybe  choose  not  to). The new code version can however choose to load the
       exact same NIF library as the old code if it wants to. Sharing the  same  dynamic  library
       will  mean  that  static  data  defined  by  the  library will be shared as well. To avoid
       unintentionally shared static data, each Erlang module code can keep its own private data.
       This  private data can be set when the NIF library is loaded and then retrieved by calling
       enif_priv_data.

       There is no way to explicitly unload a  NIF  library.  A  library  will  be  automatically
       unloaded when the module code that it belongs to is purged by the code server.

       As  mentioned  in  the  warning  text  at  the  beginning  of this document it is of vital
       importance that a native function does return relatively fast. It is hard to give an exact
       maximum amount of time that a native function is allowed to work, but as a rule of thumb a
       well behaving native function should return to its caller before a millisecond has passed.
       This  can  be  achieved using different approaches. If you have full control over the code
       that are 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.  Function
       enif_consume_timeslice can be used this facilitate such  work  division.  In  some  cases,
       however,  this  might  not  be possible, e.g. when calling third party libraries. Then you
       typically want to dispatch the work to another thread, return from  the  native  function,
       and  wait  for the result. The thread can send the result back to the calling thread using
       message passing. Information about thread primitives can be found below.

FUNCTIONALITY

       All functions that a NIF library needs to do with Erlang are performed through the NIF API
       functions. There are functions 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 was 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 the struct type  ErlNifBinary  that
           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 should only 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 operates on a binary will 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. But it does not have to happen  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  just  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  totally  opaque in nature. It can be stored and passed between
           processes on the same node, 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 that is guaranteed to still be valid. A resource object will  not  be
           deallocated  until  the  last handle term has been garbage collected by the VM and the
           resource has been 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
           that  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.

           Here 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;

           Note  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  solely  on  the  garbage collector to
           eventually deallocate the resource object when it collects the term.

           Another usage of resource objects is to create binary terms with user  defined  memory
           management. enif_make_resource_binary will create a binary term that is connected to a
           resource object. The destructor of the resource will be  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 takeover
           an already existing resource type and thereby "inherit" all existing objects  of  that
           type.  The  destructor  of the new library will thereafter be 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  will  be  postponed  as
           long as there exist resource objects with a destructor function in the library.

         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. As soon as you write towards 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 will also require synchronization if you
           treat them as mutable.

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

INITIALIZATION

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

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

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

           load, reload, upgrade and unload are pointers to functions. One  of  load,  reload  or
           upgrade  will  be  called  to  initialize the library. unload is called to release the
           library. They are all described individually below.

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

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

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

           The  library will fail to load if load returns anything other than 0. load can be NULL
           in case no initialization is needed.

         int (*upgrade)(ErlNifEnv* 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 the same as load. The only difference is that  *old_priv_data  already  contains
           the  value  set by the last call to load or reload for the old module code. *priv_data
           will be initialized to NULL when upgrade is called. It is allowed  to  write  to  both
           *priv_data and *old_priv_data.

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

         void (*unload)(ErlNifEnv* 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. Note that unload is not called
           for a replaced library as a consequence of reload.

         int (*reload)(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info):
           reload is called when the NIF library is loaded and  there  is  already  a  previously
           loaded library for this module code.

           Works  the  same  as load. The only difference is that *priv_data already contains the
           value set by the previous call to load or reload.

           The library will fail to load if reload returns anything other than 0 or if reload  is
           NULL.

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_TERM's belong to an environment (ErlNifEnv). A term can
           not 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
           and pointers to it can only be passed on to API functions.  There  are  two  types  of
           environments; process bound and process independent.

           A  process bound environment is passed as the first argument to all NIFs. All function
           arguments passed to a NIF will belong to that environment. The return value from a NIF
           must  also  be  a  term belonging to the same environment. In addition 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.

           A process independent environment is created by calling enif_alloc_env. It 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 invalidates
           it with enif_free_env or enif_send.

           All elements of a list/tuple must belong to the same  environment  as  the  list/tuple
           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[]);
         } ErlNifFunc;

           Describes  a  NIF  by  its  name,  arity  and implementation. fptr is a pointer to the
           function that implements the NIF. The argument argv of a NIF will contain the function
           arguments  passed  to  the  NIF and argc is the length of the array, i.e. the function
           arity. argv[N-1] will thus denote the Nth argument to the  NIF.  Note  that  the  argc
           argument  allows  for  the  same C function to implement several Erlang functions with
           different arity (but same name probably).

         ErlNifBinary:

         typedef struct {
             unsigned 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.

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

         ErlNifPid:
           ErlNifPid is a process identifier (pid).  In  contrast  to  pid  terms  (instances  of
           ERL_NIF_TERM),  ErlNifPid's  are  self  contained  and  not  bound to any environment.
           ErlNifPid is an opaque type.

         ErlNifResourceType:
           Each instance of ErlNifResourceType represent  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.

         ErlNifResourceDtor:

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

           The function prototype of a resource destructor function. A destructor function is not
           allowed to call any term-making functions.

         ErlNifCharEncoding:

         typedef enum {
             ERL_NIF_LATIN1
         }ErlNifCharEncoding;

           The  character  encoding  used  in  strings  and atoms. The only supported encoding is
           currently ERL_NIF_LATIN1 for iso-latin-1 (8-bit ascii).

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

         ErlNifSInt64:
           A native signed 64-bit integer type.

         ErlNifUInt64:
           A native unsigned 64-bit integer type.

EXPORTS

       void *enif_alloc(size_t size)

              Allocate memory of size bytes. Return NULL if allocation failed.

       int enif_alloc_binary(size_t size, ErlNifBinary* bin)

              Allocate  a  new  binary of size size bytes. Initialize 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.

              Return true on success or false if allocation failed.

       ErlNifEnv *enif_alloc_env()

              Allocate a new process independent environment. The environment can be used to hold
              terms that is 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.

              Return pointer to the new environment.

       void *enif_alloc_resource(ErlNifResourceType* type, unsigned size)

              Allocate a memory managed resource object of type type and size size bytes.

       void enif_clear_env(ErlNifEnv* env)

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

       int enif_compare(ERL_NIF_TERM lhs, ERL_NIF_TERM rhs)

              Return  an  integer  less  than,  equal  to,  or greater than zero if lhs is found,
              respectively, to be less than, equal, or  greater  than  rhs.  Corresponds  to  the
              Erlang operators ==, /=, =<, <, >= and > (but not =:= or =/=).

       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.

       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)

              Give  the  runtime  system  a hint about how much CPU time the current NIF call has
              consumed since last hint, or since the start of the NIF if  no  previous  hint  has
              been  given.  The  time  is  given  as a percent of the timeslice that a process is
              allowed to execute Erlang code until it may 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.

              Note that it is up to the runtime system to  determine  if  and  how  to  use  this
              information.  Implementations  on  some  platforms  may use other means in order to
              determine consumed CPU time. Lengthy NIFs should regardless of this frequently call
              enif_consume_timeslice in order to determine if it is allowed to continue execution
              or not.

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

              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.

              This function is provided to better support co-operative scheduling, improve system
              responsiveness, and make it easier to prevent misbehaviors of the VM due to  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 document.

       int enif_equal_tids(ErlNifTid tid1, ErlNifTid tid2)

              Same as erl_drv_equal_tids.

       void enif_free(void* ptr)

              Free memory allocated by enif_alloc.

       void enif_free_env(ErlNifEnv* env)

              Free  an  environment  allocated  with  enif_alloc_env.  All  terms  created in the
              environment will be freed as well.

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

              Write  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.
              Return  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)

              Set  *len  to  the length (number of bytes excluding terminating null character) of
              the atom term with encoding encode. Return true on success or false if term is  not
              an atom.

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

              Set  *dp  to  the  floating point value of term. Return true on success or false if
              term is not a float.

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

              Set *ip to the integer value of term. Return 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)

              Set  *ip  to  the integer value of term. Return 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, initialize the pid variable  *pid  from
              it  and  return  true.  Otherwise return false. No check if the process is alive is
              done.

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

              Set  *head  and  *tail  from list and return true, or return false if list is not a
              non-empty list.

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

              Set *len to the length of list term and return true, or return false if term is not
              a list.

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

              Set  *ip to the long integer value of term and return true, or return false if term
              is not an integer or is outside the bounds of type long int.

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

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

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

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

              Write 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. Return the number of bytes  written  (including  terminating  null
              character),  or -size if the string was truncated due to buffer space, or 0 if list
              is not a string that can be encoded with encode or if size was  less  than  1.  The
              written string is always null-terminated unless buffer size is less than 1.

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

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

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

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

              Set  *ip  to the unsigned integer value of term and return true, or return 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)

              Set *ip to the unsigned integer value of term and return true, or return  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)

              Set *ip to the unsigned long integer value of term and return true, or return false
              if term is not an unsigned integer or is outside the bounds of type unsigned long.

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

              Initialize  the  structure pointed to by bin with information about the binary term
              bin_term. Return 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)

              Initialize the structure pointed to by bin with one 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. Return true  on  success  or  false  if
              iolist is not an iolist.

       int enif_is_atom(ErlNifEnv* env, ERL_NIF_TERM term)

              Return true if term is an atom.

       int enif_is_binary(ErlNifEnv* env, ERL_NIF_TERM term)

              Return true if term is a binary

       int enif_is_empty_list(ErlNifEnv* env, ERL_NIF_TERM term)

              Return 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_number(ErlNifEnv* env, ERL_NIF_TERM term)

              Return true if term is a number.

       int enif_is_fun(ErlNifEnv* env, ERL_NIF_TERM term)

              Return true if term is a fun.

       int enif_is_identical(ERL_NIF_TERM lhs, ERL_NIF_TERM rhs)

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

       int enif_is_pid(ErlNifEnv* env, ERL_NIF_TERM term)

              Return true if term is a pid.

       int enif_is_port(ErlNifEnv* env, ERL_NIF_TERM term)

              Return true if term is a port.

       int enif_is_ref(ErlNifEnv* env, ERL_NIF_TERM term)

              Return true if term is a reference.

       int enif_is_tuple(ErlNifEnv* env, ERL_NIF_TERM term)

              Return true if term is a tuple.

       int enif_is_list(ErlNifEnv* env, ERL_NIF_TERM term)

              Return true if term is a list.

       int enif_keep_resource(void* obj)

              Add 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 will be destructed.

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

              Create an atom  term  from  the  null-terminated  C-string  name  with  iso-latin-1
              encoding.

       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.

       ERL_NIF_TERM enif_make_badarg(ErlNifEnv* env)

              Make a badarg exception to be returned from a NIF, and set an associated  exception
              reason  in env. If enif_make_badarg is called, the term it returns must be returned
              from the function that called it. No other return value is allowed. Also, the  term
              returned  from  enif_make_badarg may be passed only to enif_is_exception and not to
              any other NIF API function.

       ERL_NIF_TERM enif_make_binary(ErlNifEnv* env, ErlNifBinary* bin)

              Make a binary term from bin. Any ownership of the binary data will  be  transferred
              to  the created term and bin should 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)

              Make a copy of term src_term. The copy will be created in environment dst_env.  The
              source term may be located in any environment.

       ERL_NIF_TERM enif_make_double(ErlNifEnv* env, double d)

              Create a floating-point term from a double.

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

              Try to create the term of an already existing  atom  from  the  null-terminated  C-
              string  name  with  encoding  encode.  If the atom already exists store the term in
              *atom and return true, otherwise return false.

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

              Try 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 store the term in *atom and return true, otherwise return
              false.

       ERL_NIF_TERM enif_make_int(ErlNifEnv* env, int i)

              Create an integer term.

       ERL_NIF_TERM enif_make_int64(ErlNifEnv* env, ErlNifSInt64 i)

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

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

              Create 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. An empty list is returned 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)

              Create  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)

              Create a list cell [head | tail].

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

              Create an ordinary list containing the elements of array  arr  of  length  cnt.  An
              empty list is returned if cnt is 0.

       int enif_make_reverse_list(ErlNifEnv* env, ERL_NIF_TERM term, ERL_NIF_TERM *list)

              Set  *list to the reverse list of the list term and return true, or return false if
              term is not a list. This function should only be used on short lists as a copy will
              be created of the list which will not be released until after the nif returns.

       ERL_NIF_TERM enif_make_long(ErlNifEnv* env, long int i)

              Create an integer term from a long int.

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

              Allocate  a binary of size size bytes and create 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 can not be
              kept between NIF calls and it can not be reallocated.

              Return a pointer to the raw binary data and set *termp to the binary term.

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

              Make a pid term from *pid.

       ERL_NIF_TERM enif_make_ref(ErlNifEnv* env)

              Create a reference like erlang:make_ref/0.

       ERL_NIF_TERM enif_make_resource(ErlNifEnv* env, void* obj)

              Create  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,  but  note  that  the  call  to
              enif_release_resource   can   occur  immediately  after  obtaining  the  term  from
              enif_make_resource, in which case the resource object will be deallocated when  the
              term  is  garbage  collected.  See the example of creating and returning a resource
              object for more details.

              Note that the only defined behaviour of using a resource term in an Erlang  program
              is  to  store  it  and send it between processes on the same node. Other operations
              such as matching or term_to_binary will have unpredictable (but harmless) results.

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

              Create  a  binary  term that is memory managed by a resource object obj obtained by
              enif_alloc_resource. The returned binary term will consist 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 may be stored external to the
              resource object in which case it is the responsibility of the destructor to release
              the data.

              Several binary terms may be managed by the same  resource  object.  The  destructor
              will  not  be called until the last binary is garbage collected. This can be useful
              as a way 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.

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

              Create 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)

              Create 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)

              Make  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 and 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, ...)

              Create  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)

              Create  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)

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

       ERL_NIF_TERM enif_make_uint(ErlNifEnv* env, unsigned int i)

              Create an integer term from an unsigned int.

       ERL_NIF_TERM enif_make_uint64(ErlNifEnv* env, ErlNifUInt64 i)

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

       ERL_NIF_TERM enif_make_ulong(ErlNifEnv* env, unsigned long i)

              Create an integer term from an unsigned long int.

       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.

       int enif_mutex_trylock(ErlNifMutex *mtx)

              Same as erl_drv_mutex_trylock.

       void enif_mutex_unlock(ErlNifMutex *mtx)

              Same as erl_drv_mutex_unlock.

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

              Create  or  takeover  a resource type identified by the string name and give it the
              destructor function pointed to by dtor.  Argument  flags  can  have  the  following
              values:

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

                ERL_NIF_RT_TAKEOVER:
                  Open  an  existing  resource type and take over ownership of all its instances.
                  The supplied destructor dtor will be called both for existing instances as well
                  as new instances not yet created by the calling NIF library.

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

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

              Note  that  enif_open_resource_type  is  only  allowed  to  be  called in the three
              callbacks load, reload and upgrade.

       void *enif_priv_data(ErlNifEnv* env)

              Return the pointer to the private data that was set by load, reload or upgrade.

              Was previously named enif_get_data.

       int enif_realloc_binary(ErlNifBinary* bin, size_t size)

              Change the size of a binary bin. The source binary may be read-only, in which  case
              it  will  be  left  untouched and a mutable copy is allocated and assigned to *bin.
              Return true on success, false if memory allocation failed.

       void enif_release_binary(ErlNifBinary* bin)

              Release a binary obtained from enif_alloc_binary.

       void enif_release_resource(void* obj)

              Remove a reference to resource object  objobtained  from  enif_alloc_resource.  The
              resource object will be 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.

       ErlNifRWLock *enif_rwlock_create(char *name)

              Same as erl_drv_rwlock_create.

       void enif_rwlock_destroy(ErlNifRWLock *rwlck)

              Same as erl_drv_rwlock_destroy.

       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.

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

              Initialize the pid variable *pid to represent the calling process. Return pid.

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

              Send a message to a process.

                env:
                  The environment of the calling process. Must be NULL if  and  only  if  calling
                  from a created thread.

                *to_pid:
                  The  pid  of  the  receiving  process. The pid should 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.

                msg:
                  The message term to send.

              Return  true  on  success,  or  false  if  *to_pid does not refer to an alive local
              process.

              The message environment  msg_env  with  all  its  terms  (including  msg)  will  be
              invalidated  by  a  successful  call to enif_send. The environment should either be
              freed with enif_free_env of cleared for reuse with enif_clear_env.

              This function is only thread-safe when the emulator with SMP support  is  used.  It
              can only be used in a non-SMP emulator from a NIF-calling thread.

       unsigned enif_sizeof_resource(void* obj)

              Get the byte size of a resource object obj obtained by enif_alloc_resource.

       void enif_system_info(ErlNifSysInfo *sys_info_ptr, size_t size)

              Same as driver_system_info.

       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 .

       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_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_get(ErlNifTSDKey key)

              Same as erl_drv_tsd_get.

       void enif_tsd_set(ErlNifTSDKey key, void *data)

              Same as erl_drv_tsd_set.

SEE ALSO

       erlang:load_nif/2