path: root/erts/doc/src/erl_nif.xml

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<!DOCTYPE cref SYSTEM "cref.dtd">

<cref>
  <header>
    <copyright>
      <year>2001</year><year>2009</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
      Erlang Public License along with this software. If not, it can be
      retrieved online at http://www.erlang.org/.
    
      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
      the License for the specific language governing rights and limitations
      under the License.
    
    </legalnotice>

    <title>erl_nif</title>
    <prepared>Sverker Eriksson</prepared>
    <responsible>Sverker Eriksson</responsible>
    <docno>1</docno>
    <approved></approved>
    <checked></checked>
    <date>2009-11-17</date>
    <rev>PA1</rev>
    <file>erl_nif.xml</file>
  </header>
  <lib>erl_nif</lib>
  <libsummary>API functions for an Erlang NIF library</libsummary>
  <description>
     <warning><p>The NIF concept was introduced in R13B03 as an
	EXPERIMENTAL feature. The interfaces may be changed in any way
	in coming releases. The plan is however to lift the experimental label and
  maintain interface backward compatibility from R14B.</p>
  <p>Incompatible changes in <em>R13B04</em>:</p>
  <list>
    <item>The function prototypes of the NIFs have  changed to expect <c>argc</c> and <c>argv</c>
	  arguments. The arity of a NIF is by that no longer limited to 3.</item>
    <item><c>enif_get_data</c> renamed as <c>enif_priv_data</c>.</item>
    <item><c>enif_make_string</c> got a third argument for character encoding.</item>
  </list>
  </warning>

    <p>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.</p>     
    <p>A minimal example of a NIF library can look like this:</p>
      <p/>
      <code type="none">
/* 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)
</code>

    <p>and the Erlang module would have to look something like
    this:</p>
      <p/>
      <code type="none">
-module(niftest).

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

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

hello() ->
      "NIF library not loaded".
</code>
    <p>and compile and test something like this (on Linux):</p>
      <p/>
      <code type="none">
$> 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!"
</code>

     <p>A better solution for a real module is to take advantage of
     the new directive <seealso
     marker="doc/reference_manual:code_loading#on_load">on_load</seealso> to automatically
     load the NIF library when the module is loaded.</p>
     <note><p>A NIF must be exported or used locally by the module (or both).
     An unused local stub function will be optimized away by the compiler
      causing loading of the NIF library to fail.</p>
    </note>
     <p>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 <seealso marker="#enif_priv_data">enif_priv_data()</seealso>.</p>
    <p>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. A NIF library will also be unloaded if it is replaced
     by another version of the library by a second call to
     <c>erlang:load_nif/2</c> from the same module code.</p> 
  </description>
  <section>
  <title>FUNCTIONALITY</title>
  <p>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:</p>
    <taglist>
      <tag>Read and write Erlang terms</tag>
      <item><p>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 <c>ERL_NIF_TERM</c>
      and can only be read or written using API functions. Most functions to read
      the content of a term are prefixed <c>enif_get_</c> and usually return
      true (or false) if the term was of the expected type (or not).    
      The functions to write terms are all prefixed <c>enif_make_</c> and usually
      return the created <c>ERL_NIF_TERM</c>. There are also some functions
      to query terms, like <c>enif_is_atom</c>, <c>enif_is_identical</c> and
      <c>enif_compare</c>.</p></item>
      <tag>Binaries</tag>
      <item><p>Terms of type binary are accessed with the help of the struct type
      <seealso marker="#ErlNifBinary">ErlNifBinary</seealso>    
      that contains a pointer (<c>data</c>) to the raw binary data and the length
      (<c>size</c>) of the data in bytes. Both <c>data</c> and <c>size</c> are
      read-only and should only be written using calls to API functions.
      Instances of <c>ErlNifBinary</c> are however always allocated by the user
      (usually as local variables).</p>
      <p>The raw data pointed to by <c>data</c> is only mutable after a call to
      <seealso marker="#enif_alloc_binary">enif_alloc_binary</seealso> or
      <seealso marker="#enif_realloc_binary">enif_realloc_binary</seealso>.
      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
      <seealso marker="#enif_release_binary">enif_release_binary</seealso>
      or made read-only by transferring it to an Erlang term with
      <seealso marker="#enif_make_binary">enif_make_binary</seealso>.
      But it does not have to happen in the same NIF call. Read-only binaries
      do not have to be released.</p>
      <p><seealso marker="#enif_make_new_binary">enif_make_new_binary</seealso>
      can be used as a shortcut to allocate and return a binary in the same NIF call.</p>
      <p>Binaries are sequences of whole bytes. Bitstrings with an arbitrary
      bit length have no support yet.</p>
       </item>
      <tag>Resource objects</tag>
      <item><p>The use of resource objects is a way to return pointers to
      native data structures from a NIF in a safe way. A resource object is
      just a block of memory allocated with
      <seealso marker="#enif_alloc_resource">enif_alloc_resource()</seealso>.
      A handle ("safe pointer") to this memory block can then be returned to Erlang by the use of
      <seealso marker="#enif_make_resource">enif_make_resource()</seealso>.
      The term returned by <c>enif_make_resource</c>
      is totally opaque in nature. It can be stored and passed between processses
      on the same node, but the only real end usage is to pass it back as argument to a NIF.
      The NIF can then do <seealso marker="#enif_get_resource">enif_get_resource()</seealso>
      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 <seealso marker="#enif_release_resource">enif_release_resource()</seealso>
      (not necessarily in that order).</p>      
      <p>All resource objects are created as instances of some <em>resource type</em>.
      This makes resources from different modules to be distinguishable. 
      A resource type is created by calling
      <seealso marker="#enif_open_resource_type">enif_open_resource_type()</seealso>
      when a library is loaded. Objects of that resource type can then later be allocated
      and <c>enif_get_resource</c> 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 <c>enif_release_resource</c>). Resource types
      are uniquely identified by a supplied name string.</p>
      <p>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.
      </p>
      <p>Here is a template example of how to create and return a resource object.</p>
      <p/>
      <code type="none">
    ERL_NIF_TERM term;
    MyStruct* ptr = enif_alloc_resource(env, my_resource_type, sizeof(MyStruct));

    /* initialize struct ... */

    term = enif_make_resource(env, ptr);

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

      </item>
      <tag>Threads and concurrency</tag>
      <item><p>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 <seealso marker="#enif_priv_data">enif_priv_data</seealso>
      you need to supply your own explicit synchronization. Resource objects
      will also require synchronization if you treat them as mutable.</p>
      <p>The library initialization callbacks <c>load</c>, <c>reload</c> and
      <c>upgrade</c> are all thread-safe even for shared state data.</p>
      <p>Avoid doing lengthy work in NIF calls as that may degrade the
      responsiveness of the VM. NIFs are called directly by the same scheduler
      thread that executed the calling Erlang code. The calling scheduler will thus
      be blocked from doing any other work until the NIF returns.</p>
      </item>
    </taglist>
  </section>
  <section>
    <title>INITIALIZATION</title>
    <taglist>
      <tag><marker id="ERL_NIF_INIT"/>ERL_NIF_INIT(MODULE, ErlNifFunc funcs[], load, reload, upgrade, unload)</tag>
      <item><p>This is the magic macro to initialize a NIF library. It
      should be evaluated in global file scope.</p>
      <p><c>MODULE</c> is the name of the Erlang module as an
      identifier without string quotations. It will be stringified by
      the macro.</p>
      <p><c>funcs</c> is a static array of function descriptors for
      all the implemented NIFs in this library.</p>
      <p><c>load</c>, <c>reload</c>, <c>upgrade</c> and <c>unload</c>
      are pointers to functions. One of <c>load</c>, <c>reload</c> or
      <c>upgrade</c> will be called to initialize the library.
      <c>unload</c> is called to release the library. They are all
      described individually below.</p>
      </item>

      <tag><marker id="load"/>int (*load)(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)</tag>
       <item><p><c>load</c> is called when the NIF library is loaded
        and there is no previously loaded library for this module.</p>
        <p><c>*priv_data</c> can be set to point to some private data
           that the library needs in order to keep a state between NIF
           calls. <c>enif_priv_data()</c> will return this pointer.
           <c>*priv_data</c> will be initialized to NULL when <c>load</c> is
           called.</p> 
        <p><c>load_info</c> is the second argument to <seealso
           marker="erlang#load_nif-2">erlang:load_nif/2</seealso>.</p>
        <p>The library will fail to load if <c>load</c> returns
           anything other than 0. <c>load</c> can be NULL in case no
           initialization is needed.</p> 
       </item>

      <tag><marker id="reload"/>int (*reload)(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)</tag>
       <item><p><c>reload</c> is called when the NIF library is loaded
        and there is already a previously loaded library for this
        module code.</p>
        <p>Works the same as <c>load</c>. The only difference is that
        <c>*priv_data</c> already contains the value set by the
        previous call to <c>load</c> or <c>reload</c>.</p>
        <p>The library will fail to load if <c>reload</c> returns
           anything other than 0 or if <c>reload</c> is NULL.</p> 
      </item>

      <tag><marker id="upgrade"/>int (*upgrade)(ErlNifEnv* env, void** priv_data, void** old_priv_data, ERL_NIF_TERM load_info)</tag>
       <item><p><c>upgrade</c> is called when the NIF library is loaded
        and there is no previously loaded library for this module
        code, BUT there is old code of this module with a loaded NIF library.</p>
        <p>Works the same as <c>load</c>. The only difference is that
        <c>*old_priv_data</c> already contains the value set by the
         last call to <c>load</c> or <c>reload</c> for the old module
         code. <c>*priv_data</c> will be initialized to NULL when <c>upgrade</c>
         is called. It is allowed to write to both *priv_data and *old_priv_data.</p> 
        <p>The library will fail to load if <c>upgrade</c> returns
           anything other than 0 or if <c>upgrade</c> is NULL.</p>
      </item>

      <tag><marker id="unload"/>void (*unload)(ErlNifEnv* env, void* priv_data)</tag>
       <item><p><c>unload</c> 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 <c>unload</c> is not
       called for a replaced library as a consequence of <c>reload</c>.</p>
      </item>

    </taglist>
  </section>

  <section>
    <title>DATA TYPES</title>

    <taglist>
      <tag><marker id="ERL_NIF_TERM"/>ERL_NIF_TERM</tag>
       <item>
        <p>Variables of type <c>ERL_NIF_TERM</c> 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. A variable of
        type <c>ERL_NIF_TERM</c> is only valid until the NIF call, where it was
        obtained, returns.</p>
      </item>
     <tag><marker id="ErlNifEnv"/>ErlNifEnv</tag>
      <item>
        <p><c>ErlNifEnv</c> contains information about the context in
          which a NIF call is made. This pointer should not be
          dereferenced in any way, but only passed on to API
          functions. An <c>ErlNifEnv</c> pointer is only valid until
          the function, where it was supplied as argument,
          returns. It is thus useless and dangerous to store <c>ErlNifEnv</c>
          pointers in between NIF calls.</p>
      </item>
    <tag><marker id="ErlNifFunc"/>ErlNifFunc</tag>
     <item>
      <p/>
      <code type="none">
typedef struct {
    const char* <em>name</em>;
    unsigned <em>arity</em>;
    ERL_NIF_TERM (*<em>fptr</em>)(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
} ErlNifFunc;
</code>
        <p>Describes a NIF by its name, arity and implementation.
        <c>fptr</c> is a pointer to the function that implements the
        NIF. The argument <c>argv</c> of a NIF will contain the
        function arguments passed to the NIF and <c>argc</c> is the
        length of the array, i.e. the function arity. <c>argv[N-1]</c>
        will thus denote the Nth argument to the NIF. Note that the
        <c>argc</c> argument allows for the same C function to
        implement several Erlang functions with different arity (but
        same name probably).</p>
      </item>
    <tag><marker id="ErlNifBinary"/>ErlNifBinary</tag>
     <item>
      <p/>
      <code type="none">
typedef struct {
    unsigned <em>size</em>;
    unsigned char* <em>data</em>;
} ErlNifBinary;
</code>
        <p><c>ErlNifBinary</c> contains transient information about an
          inspected binary term. <c>data</c> is a pointer to a buffer
          of <c>size</c> bytes with the raw content of the binary.</p>
      </item>
      <tag><marker id="ErlNifResourceType"/>ErlNifResourceType</tag>
       <item>
          <p>Each instance of <c>ErlNifResourceType</c> 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.</p>
        </item>
        <tag><marker id="ErlNifResourceDtor"/>ErlNifResourceDtor</tag>
         <item>
           <p/>
           <code type="none">
typedef void ErlNifResourceDtor(ErlNifEnv* env, void* obj);
</code>
            <p>The function prototype of a resource destructor function.
            A destructor function is not allowed to call any term-making functions.</p>
          </item>
          <tag><marker id="ErlNifCharEncoding"/>ErlNifCharEncoding</tag>
           <item>
             <p/>
             <code type="none">
typedef enum {
    ERL_NIF_LATIN1
}ErlNifCharEncoding;
</code>
              <p>The character encoding used in strings. The only supported
              encoding is currently <c>ERL_NIF_LATIN1</c> for iso-latin-1
              (8-bit ascii).</p>
            </item>
            <tag><marker id="ErlNifSysInfo"/>ErlNifSysInfo</tag>
             <item>
                <p>Used by <seealso marker="#enif_system_info">enif_system_info</seealso>
                to return information about the runtime system. Contains currently
                the exact same content as <seealso marker="erl_driver#ErlDrvSysInfo">ErlDrvSysInfo</seealso>.</p>
              </item>

    </taglist>
  </section>

  <funcs>
    <func><name><ret>void*</ret><nametext>enif_alloc(ErlNifEnv* env, size_t size)</nametext></name>
      <fsummary>Allocate dynamic memory.</fsummary>
      <desc><p>Allocate memory of <c>size</c> bytes. Return NULL if allocation failed.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_alloc_binary(ErlNifEnv* env, unsigned size, ErlNifBinary* bin)</nametext></name>
      <fsummary>Create a new binary.</fsummary>
      <desc><p>Allocate a new binary of size <c>size</c>
      bytes. Initialize the structure pointed to by <c>bin</c> to
      refer to the allocated binary. The binary must either be released by 
      <seealso marker="#enif_release_binary">enif_release_binary()</seealso> 
      or ownership transferred to an Erlang term with 
      <seealso marker="#enif_make_binary">enif_make_binary()</seealso>. 
      An allocated (and owned) <c>ErlNifBinary</c> can be kept between NIF
      calls.</p>
        <p>Return false if allocation failed.</p>
      </desc>
    </func>
    <func><name><ret>void*</ret><nametext>enif_alloc_resource(ErlNifEnv* env, ErlNifResourceType* type, unsigned size)</nametext></name>
      <fsummary>Allocate a memory managed resource object</fsummary>
      <desc><p>Allocate a memory managed resource object of type <c>type</c> and size <c>size</c> bytes.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_compare(ErlNifEnv* env, ERL_NIF_TERM lhs, ERL_NIF_TERM rhs)</nametext></name>
      <fsummary>Compare two terms</fsummary>
      <desc><p>Return an integer less than, equal to, or greater than
      zero if <c>lhs</c> is found, respectively, to be less than,
      equal, or greater than <c>rhs</c>. Corresponds to the Erlang
      operators <c>==</c>, <c>/=</c>, <c>=&lt;</c>, <c>&lt;</c>,
      <c>&gt;=</c> and <c>&gt;</c> (but <em>not</em> <c>=:=</c> or <c>=/=</c>).</p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_cond_broadcast(ErlNifCond *cnd)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_broadcast">erl_drv_cond_broadcast()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>ErlNifCond*</ret><nametext>enif_cond_create(char *name)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_create">erl_drv_cond_create()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_cond_destroy(ErlNifCond *cnd)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_destroy">erl_drv_cond_destroy()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_cond_signal(ErlNifCond *cnd)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_signal">erl_drv_cond_signal()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_cond_wait(ErlNifCond *cnd, ErlNifMutex *mtx)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_wait">erl_drv_cond_wait()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_equal_tids(ErlNifTid tid1, ErlNifTid tid2)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_equal_tids">erl_drv_equal_tids()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_free(ErlNifEnv* env, void* ptr)</nametext></name>
      <fsummary>Free dynamic memory</fsummary>
      <desc><p>Free memory allocated by <c>enif_alloc</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_atom(ErlNifEnv* env, 
                  ERL_NIF_TERM term, char* buf, unsigned size)
                             </nametext></name>
      <fsummary>Get the text representation of an atom term</fsummary>
      <desc><p>Write a null-terminated string, in the buffer pointed to by
              <c>buf</c> of size <c>size</c>, consisting of the string 
              representation of the atom <c>term</c>. Return the number of bytes
              written (including terminating null character) or 0 if
              <c>term</c> is not an atom with maximum length of 
              <c>size-1</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_atom_length(ErlNifEnv* env, ERL_NIF_TERM term, unsigned* len)</nametext></name>
      <fsummary>Get the length of atom <c>term</c>.</fsummary>
      <desc><p>Set <c>*len</c> to the length (number of bytes excluding
      terminating null character) of <c>term</c> or return false if
      <c>term</c> is not an atom.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_double(ErlNifEnv* env, ERL_NIF_TERM term, double* dp)</nametext></name>
      <fsummary>Read a floating-point number term.</fsummary>
      <desc><p>Set <c>*dp</c> to the floating point value of
      <c>term</c> or return false if <c>term</c> is not a float.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_int(ErlNifEnv* env, ERL_NIF_TERM term, int* ip)</nametext></name>
      <fsummary>Read an integer term.</fsummary>
      <desc><p>Set <c>*ip</c> to the integer value of
      <c>term</c> or return false if <c>term</c> is not an integer or is
      outside the bounds of type <c>int</c></p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_list_cell(ErlNifEnv* env, ERL_NIF_TERM list, ERL_NIF_TERM* head, ERL_NIF_TERM* tail)</nametext></name>
      <fsummary>Get head and tail from a list</fsummary>
      <desc><p>Set <c>*head</c> and <c>*tail</c> from
      <c>list</c> or return false if <c>list</c> is not a non-empty
      list.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_list_length(ErlNifEnv* env, ERL_NIF_TERM term, unsigned* len)</nametext></name>
      <fsummary>Get the length of list <c>term</c>.</fsummary>
      <desc><p>Set <c>*len</c> to the length of <c>term</c> or return
      false if <c>term</c> is not a list.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_long(ErlNifEnv* env, ERL_NIF_TERM term, long int* ip)</nametext></name>
      <fsummary>Read an long integer term.</fsummary>
      <desc><p>Set <c>*ip</c> to the long integer value of
      <c>term</c> or return false if <c>term</c> is not an integer or is
      outside the bounds of type <c>long int</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_resource(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifResourceType* type, void** objp)</nametext></name>
      <fsummary>Get the pointer to a resource object</fsummary>
      <desc><p>Set <c>*objp</c> to point to the resource object referred to by <c>term</c>.
      The pointer is valid until the calling NIF returns and should not be released.</p>
      <p>Return false if <c>term</c> is not a handle to a resource object
      of type <c>type</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_string(ErlNifEnv* env, 
                                ERL_NIF_TERM list, char* buf, unsigned size,
                                ErlNifCharEncoding encode)</nametext></name>
      <fsummary>Get a C-string from a list.</fsummary>
      <desc><p>Write a null-terminated string, in the buffer pointed to by
              <c>buf</c> with size <c>size</c>, consisting of the characters
              in the string <c>list</c>. The characters are written using encoding
              <seealso marker="#ErlNifCharEncoding">encode</seealso>.
              Return the number of bytes written (including terminating null
              character), or <c>-size</c> if the string was truncated due to
              buffer space, or 0 if <c>list</c> is not a string that can be
              encoded with <c>encode</c> or if <c>size</c> was less than 1.              
              The written string is always null-terminated unless buffer
              <c>size</c> is less than 1.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_tuple(ErlNifEnv* env, ERL_NIF_TERM term, int* arity, const ERL_NIF_TERM** array)</nametext></name>
      <fsummary>Inspect the elements of a tuple.</fsummary>
      <desc><p>If <c>term</c> is a tuple, set <c>*array</c> to point
      to an array containing the elements of the tuple and set
      <c>*arity</c> to the number of elements. Note that the array
      is read-only and <c>(*array)[N-1]</c> will be the Nth element of
      the tuple. <c>*array</c> is undefined if the arity of the tuple
      is zero.</p><p>Return false if <c>term</c> is not a
      tuple.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_get_uint(ErlNifEnv* env, ERL_NIF_TERM term, unsigned int* ip)</nametext></name>
      <fsummary>Read an unsigned integer term.</fsummary>
      <desc><p>Set <c>*ip</c> to the unsigned integer value of
      <c>term</c> or return false if <c>term</c> is not an unsigned integer or is
      outside the bounds of type <c>unsigned int</c></p></desc>
    </func>

    <func><name><ret>int</ret><nametext>enif_get_ulong(ErlNifEnv* env, ERL_NIF_TERM term, unsigned long* ip)</nametext></name>
      <fsummary>Read an unsigned integer term.</fsummary>
      <desc><p>Set <c>*ip</c> to the unsigned long integer value of
      <c>term</c> or return false if <c>term</c> is not an unsigned integer or is
      outside the bounds of type <c>unsigned long</c></p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_inspect_binary(ErlNifEnv* env, ERL_NIF_TERM bin_term, ErlNifBinary* bin)</nametext></name>
      <fsummary>Inspect the content of a binary</fsummary>
      <desc><p>Initialize the structure pointed to by <c>bin</c> with 
              information about the binary term
      <c>bin_term</c>. Return false if <c>bin_term</c> is not a binary.</p></desc> 
    </func>
    <func><name><ret>int</ret><nametext>enif_inspect_iolist_as_binary(ErlNifEnv* 
                                env, ERL_NIF_TERM term, ErlNifBinary* bin)
                              </nametext></name>
      <fsummary>Inspect the content of an iolist</fsummary>
      <desc><p>Initialize the structure pointed to by <c>bin</c> with one
      continuous buffer with the same byte content as <c>iolist</c>. As with 
      inspect_binary, the data pointed to by <c>bin</c> is transient and does 
      not need to be released. Return false if <c>iolist</c> is not an
      iolist.</p>
      </desc> 
    </func>
    <func><name><ret>int</ret><nametext>enif_is_atom(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is an atom</fsummary>
      <desc><p>Return true if <c>term</c> is an atom.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_binary(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a binary</fsummary>
      <desc><p>Return true if <c>term</c> is a binary</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_empty_list(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is an empty list</fsummary>
      <desc><p>Return true if <c>term</c> is an empty list.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_fun(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a fun</fsummary>
      <desc><p>Return true if <c>term</c> is a fun.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_identical(ErlNifEnv* env, ERL_NIF_TERM lhs, ERL_NIF_TERM rhs)</nametext></name>
      <fsummary>Erlang operator =:=</fsummary>
      <desc><p>Return true if the two terms are identical. Corresponds to the
      Erlang operators <c>=:=</c> and
      <c>=/=</c>.</p></desc> 
    </func>
    <func><name><ret>int</ret><nametext>enif_is_pid(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a pid</fsummary>
      <desc><p>Return true if <c>term</c> is a pid.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_port(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a port</fsummary>
      <desc><p>Return true if <c>term</c> is a port.</p></desc>
    </func>

    <func><name><ret>int</ret><nametext>enif_is_ref(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a reference</fsummary>
      <desc><p>Return true if <c>term</c> is a reference.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_tuple(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a tuple</fsummary>
      <desc><p>Return true if <c>term</c> is a tuple.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_is_list(ErlNifEnv* env, ERL_NIF_TERM term)</nametext></name>
      <fsummary>Determine if a term is a list</fsummary>
      <desc><p>Return true if <c>term</c> is a list.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_atom(ErlNifEnv* env, const char* name)</nametext></name>
      <fsummary>Create an atom term</fsummary>
      <desc><p>Create an atom term from the null-terminated C-string <c>name</c>.
      Unlike other terms, atom terms may be saved and used between NIF calls.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_atom_len(ErlNifEnv* env, const char* name, size_t len)</nametext></name>
      <fsummary>Create an atom term</fsummary>
      <desc><p>Create an atom term from the string <c>name</c> with length <c>len</c>.
      Null-characters are treated as any other characters.
      Unlike other terms, atom terms may be saved and used between NIF calls.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_badarg(ErlNifEnv* env)</nametext></name>
      <fsummary>Make a badarg exception.</fsummary>
      <desc><p>Make a badarg exception to be returned from a NIF.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_binary(ErlNifEnv* env, ErlNifBinary* bin)</nametext></name>
      <fsummary>Make a binary term.</fsummary>
      <desc><p>Make a binary term from <c>bin</c>. Any ownership of 
              the binary data will be transferred to the created term and
              <c>bin</c> should be considered read-only for the rest of the NIF
              call and then as released.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_double(ErlNifEnv* env, double d)</nametext></name>
      <fsummary>Create a floating-point term</fsummary>
      <desc><p>Create a floating-point term from a <c>double</c>.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_make_existing_atom(ErlNifEnv* env, const char* name, ERL_NIF_TERM* atom)</nametext></name>
      <fsummary>Create an existing atom term</fsummary>
      <desc><p>Try to create the term of an already existing atom from
      the null-terminated C-string <c>name</c>. If the atom already exists store the
      term in <c>*atom</c> and return true, otherwise return
      false.</p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_make_existing_atom_len(ErlNifEnv* env, const char* name, size_t len, ERL_NIF_TERM* atom)</nametext></name>
      <fsummary>Create an existing atom term</fsummary>
      <desc><p>Try to create the term of an already existing atom from the
      string <c>name</c> with length <c>len</c>. Null-characters are treated
      as any other characters. If the atom already exists store the term
      in <c>*atom</c> and return true, otherwise return false.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_int(ErlNifEnv* env, int i)</nametext></name>
      <fsummary>Create an integer term</fsummary>
      <desc><p>Create an integer term.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list(ErlNifEnv* env, unsigned cnt, ...)</nametext></name>
      <fsummary>Create a list term.</fsummary>
      <desc><p>Create an ordinary list term of length <c>cnt</c>. Expects
      <c>cnt</c> number of arguments (after <c>cnt</c>) of type ERL_NIF_TERM as the
      elements of the list. An empty list is returned if <c>cnt</c> is 0.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list1(ErlNifEnv* env, ERL_NIF_TERM e1)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list2(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list3(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list4(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list5(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list6(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list7(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list8(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list9(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9)</nametext></name>
      <fsummary>Create a list term.</fsummary>
      <desc><p>Create an ordinary list term with length indicated by the
      function name. Prefer these functions (macros) over the variadic
      <c>enif_make_list</c>  to get a compile time error if the number of
      arguments does not match.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list_cell(ErlNifEnv* env, ERL_NIF_TERM head, ERL_NIF_TERM tail)</nametext></name>
      <fsummary>Create a list cell.</fsummary>
      <desc><p>Create a list cell <c>[head | tail]</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_list_from_array(ErlNifEnv* env, const ERL_NIF_TERM arr[], unsigned cnt)</nametext></name>
      <fsummary>Create a list term from an array.</fsummary>
      <desc><p>Create an ordinary list containing the elements of array <c>arr</c>
      of length <c>cnt</c>. An empty list is returned if <c>cnt</c> is 0.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_long(ErlNifEnv* env, long int i)</nametext></name>
      <fsummary>Create an integer term from a long int</fsummary>
      <desc><p>Create an integer term from a <c>long int</c>.</p></desc>
    </func>
    <func><name><ret>unsigned char*</ret><nametext>enif_make_new_binary(ErlNifEnv* env, unsigned size, ERL_NIF_TERM* termp)</nametext></name>
      <fsummary>Allocate and create a new binary term</fsummary>
      <desc><p>Allocate a binary of size <c>size</c> 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
      <seealso marker="#ErlNifBinary">ErlNifBinary</seealso>. The drawbacks are
      that the binary can not be kept between NIF calls and it can not be
      reallocated.</p><p>Return a pointer to the raw binary data and set
      <c>*termp</c> to the binary term.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_ref(ErlNifEnv* env)</nametext></name>
      <fsummary>Create a reference.</fsummary>
      <desc><p>Create a reference like <seealso marker="erlang#make_ref-0">erlang:make_ref/0</seealso>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_resource(ErlNifEnv* env, void* obj)</nametext></name>
      <fsummary>Create an opaque handle to a resource object</fsummary>
      <desc><p>Create an opaque handle to a memory managed resource object
      obtained by <seealso marker="#enif_alloc_resource">enif_alloc_resource</seealso>.
      No ownership transfer is done, the resource object still needs to be released by
      <seealso marker="#enif_release_resource">enif_release_resource</seealso>.</p>
      <p>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 <c>term_to_binary</c>
      will have unpredictable (but harmless) results.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_string(ErlNifEnv* env, const char* string, ErlNifCharEncoding encoding)</nametext></name>
      <fsummary>Create a string.</fsummary>
      <desc><p>Create a list containing the characters of the
      null-terminated string <c>string</c> with encoding <seealso marker="#ErlNifCharEncoding">encoding</seealso>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_string_len(ErlNifEnv* env, const char* string, size_t len, ErlNifCharEncoding encoding)</nametext></name>
      <fsummary>Create a string.</fsummary>
      <desc><p>Create a list containing the characters of the string <c>string</c> with
      length <c>len</c> and encoding <seealso marker="#ErlNifCharEncoding">encoding</seealso>.
      Null-characters are treated as any other characters.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_sub_binary(ErlNifEnv* 
      env, ERL_NIF_TERM bin_term, unsigned pos, unsigned size)</nametext></name>
      <fsummary>Make a subbinary term.</fsummary>
      <desc><p>Make a subbinary of binary <c>bin_term</c>, starting at 
              zero-based position <c>pos</c> with a length of <c>size</c> bytes. 
              <c>bin_term</c> must be a binary or bitstring and
              <c>pos+size</c> must be less or equal to the number of whole
              bytes in <c>bin_term</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple(ErlNifEnv* env, unsigned cnt, ...)</nametext></name>
      <fsummary>Create a tuple term.</fsummary>
      <desc><p>Create a tuple term of arity <c>cnt</c>. Expects
      <c>cnt</c> number of arguments (after <c>cnt</c>) of type ERL_NIF_TERM as the
      elements of the tuple.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple1(ErlNifEnv* env, ERL_NIF_TERM e1)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple2(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple3(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple4(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple5(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple6(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple7(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple8(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8)</nametext></name>
    <name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple9(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9)</nametext></name>
      <fsummary>Create a tuple term.</fsummary>
      <desc><p>Create a tuple term with length indicated by the
      function name. Prefer these functions (macros) over the variadic
      <c>enif_make_tuple</c>  to get a compile time error if the number of
      arguments does not match.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_tuple_from_array(ErlNifEnv* env, const ERL_NIF_TERM arr[], unsigned cnt)</nametext></name>
      <fsummary>Create a tuple term from an array.</fsummary>
      <desc><p>Create a tuple containing the elements of array <c>arr</c>
      of length <c>cnt</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_uint(ErlNifEnv* env, unsigned int i)</nametext></name>
      <fsummary>Create an unsigned integer term</fsummary>
      <desc><p>Create an integer term from an <c>unsigned int</c>.</p></desc>
    </func>
    <func><name><ret>ERL_NIF_TERM</ret><nametext>enif_make_ulong(ErlNifEnv* env, unsigned long i)</nametext></name>
      <fsummary>Create an integer term from an unsigned long int</fsummary>
      <desc><p>Create an integer term from an <c>unsigned long int</c>.</p></desc>
    </func>
    <func><name><ret>ErlNifMutex*</ret><nametext>enif_mutex_create(char *name)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_create">erl_drv_mutex_create()</seealso>.
    </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_mutex_destroy(ErlNifMutex *mtx)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_destroy">erl_drv_mutex_destroy()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_mutex_lock(ErlNifMutex *mtx)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_lock">erl_drv_mutex_lock()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_mutex_trylock(ErlNifMutex *mtx)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_trylock">erl_drv_mutex_trylock()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_mutex_unlock(ErlNifMutex *mtx)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_unlock">erl_drv_mutex_unlock()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>ErlNifResourceType*</ret><nametext>enif_open_resource_type(ErlNifEnv* env, const char* name,
                             ErlNifResourceDtor* dtor, ErlNifResourceFlags flags, ErlNifResourceFlags* tried)</nametext></name>
      <fsummary>Create or takeover a resource type</fsummary>
      <desc><p>Create or takeover a resource type identified by the string
      <c>name</c> and give it the destructor function pointed to by <seealso marker="#ErlNifResourceDtor">dtor</seealso>.
      Argument <c>flags</c> can have the following values:</p>
      <taglist>
        <tag><c>ERL_NIF_RT_CREATE</c></tag>
              <item>Create a new resource type that does not already exist.</item>
        <tag><c>ERL_NIF_RT_TAKEOVER</c></tag>
              <item>Open an existing resource type and take over ownership of all its instances.
               The supplied destructor <c>dtor</c> will be called both for existing instances
               as well as new instances not yet created by the calling NIF library.</item>            
      </taglist>
      <p>The two flag values can be combined with bitwise-or. To avoid unintentional
      name clashes a good practice is to include the module name as part of the
      type <c>name</c>. The <c>dtor</c> may  be <c>NULL</c> in case no destructor
      is needed.</p>
      <p>On success, return a pointer to the resource type and <c>*tried</c>
      will be set to either <c>ERL_NIF_RT_CREATE</c> or
      <c>ERL_NIF_RT_TAKEOVER</c> to indicate what was actually done.
       On failure, return <c>NULL</c> and set <c>*tried</c> to <c>flags</c>.
       It is allowed to set <c>tried</c> to <c>NULL</c>.</p>
       <p>Note that <c>enif_open_resource_type</c> is only allowed to be called in the three callbacks
       <seealso marker="#load">load</seealso>, <seealso marker="#reload">reload</seealso>
       and <seealso marker="#upgrade">upgrade</seealso>.</p>
      </desc>
    </func>
    <func><name><ret>void*</ret><nametext>enif_priv_data(ErlNifEnv* env)</nametext></name>
      <fsummary>Get the private data of a NIF library</fsummary>
      <desc><p>Return the pointer to the private data that was set by <c>load</c>,
      <c>reload</c> or <c>upgrade</c>.</p>
      <p>Was previously named <c>enif_get_data</c>.</p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_realloc_binary(ErlNifEnv* env, ErlNifBinary* bin, unsigned size)</nametext></name>
      <fsummary>Change the size of a binary.</fsummary>
      <desc><p>Change the size of a binary <c>bin</c>. The source binary
      may be read-only, in which case it will be left untouched and
      a mutable copy is allocated and assigned to <c>*bin</c>.</p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_release_binary(ErlNifEnv* env, ErlNifBinary* bin)</nametext></name>
      <fsummary>Release a binary.</fsummary>
      <desc><p>Release a binary obtained 
              from <c>enif_alloc_binary</c>.</p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_release_resource(ErlNifEnv* env, void* obj)</nametext></name>
      <fsummary>Release a resource object.</fsummary>
      <desc><p>Release a resource object obtained from <c>enif_alloc_resource</c>.
      The object may still be alive if it is referred to by Erlang terms. Each call to
      <c>enif_release_resource</c> must correspond to a previous call to <c>enif_alloc_resource</c>.
      References made by <c>enif_make_resource</c> can only be released by the garbage collector.</p></desc>
    </func>
    <func><name><ret>ErlNifRWLock*</ret><nametext>enif_rwlock_create(char *name)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_create">erl_drv_rwlock_create()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_rwlock_destroy(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_destroy">erl_drv_rwlock_destroy()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_rwlock_rlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_rlock">erl_drv_rwlock_rlock()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_rwlock_runlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_runlock">erl_drv_rwlock_runlock()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_rwlock_rwlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_rwlock">erl_drv_rwlock_rwlock()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_rwlock_rwunlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_rwunlock">erl_drv_rwlock_rwunlock()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_rwlock_tryrlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_tryrlock">erl_drv_rwlock_tryrlock()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_rwlock_tryrwlock(ErlNifRWLock *rwlck)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_tryrwlock">erl_drv_rwlock_tryrwlock()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>unsigned</ret><nametext>enif_sizeof_resource(ErlNifEnv* env, void* obj)</nametext></name>
      <fsummary>Get the byte size of a resource object</fsummary>
      <desc><p>Get the byte size of a resource object <c>obj</c> obtained by
      <c>enif_alloc_resource</c>.</p></desc>
    </func>
    <func>
      <name><ret>void</ret><nametext>enif_system_info(ErlNifSysInfo *sys_info_ptr, size_t size)</nametext></name>
      <fsummary>Get information about the Erlang runtime system</fsummary>
      <desc><p>Same as <seealso marker="erl_driver#driver_system_info">driver_system_info()</seealso>.
            </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_thread_create(char *name,ErlNifTid *tid,void * (*func)(void *),void *args,ErlNifThreadOpts *opts)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_create">erl_drv_thread_create()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_thread_exit(void *resp)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_exit">erl_drv_thread_exit()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_thread_join(ErlNifTid, void **respp)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_join">erl_drv_thread_join ()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>ErlNifThreadOpts*</ret><nametext>enif_thread_opts_create(char *name)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_opts_create">erl_drv_thread_opts_create()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_thread_opts_destroy(ErlNifThreadOpts *opts)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_opts_destroy">erl_drv_thread_opts_destroy()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>ErlNifTid</ret><nametext>enif_thread_self(void)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_self">erl_drv_thread_self()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>int</ret><nametext>enif_tsd_key_create(char *name, ErlNifTSDKey *key)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_tsd_key_create">erl_drv_tsd_key_create()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_tsd_key_destroy(ErlNifTSDKey key)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_tsd_key_destroy">erl_drv_tsd_key_destroy()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void*</ret><nametext>enif_tsd_get(ErlNifTSDKey key)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_tsd_get">erl_drv_tsd_get()</seealso>.
          </p></desc>
    </func>
    <func><name><ret>void</ret><nametext>enif_tsd_set(ErlNifTSDKey key, void *data)</nametext></name>
    <fsummary></fsummary>
    <desc><p>Same as <seealso marker="erl_driver#erl_drv_tsd_set">erl_drv_tsd_set()</seealso>.
          </p></desc>
    </func>
  </funcs>
  <section>
    <title>SEE ALSO</title>
    <p><seealso marker="erlang#load_nif-2">load_nif(3)</seealso></p>
  </section>
</cref>