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-rw-r--r--erts/doc/src/erl_nif.xml363
1 files changed, 293 insertions, 70 deletions
diff --git a/erts/doc/src/erl_nif.xml b/erts/doc/src/erl_nif.xml
index b5dc9037c4..05b519fe7d 100644
--- a/erts/doc/src/erl_nif.xml
+++ b/erts/doc/src/erl_nif.xml
@@ -80,7 +80,7 @@
<code type="none">
/* niftest.c */
-#include "erl_nif.h"
+#include &lt;erl_nif.h&gt;
static ERL_NIF_TERM hello(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
{
@@ -123,7 +123,7 @@ ok
"Hello world!"</code>
<p>A better solution for a real module is to take advantage of the new
- directive <c>on load</c> (see section
+ directive <c>on_load</c> (see section
<seealso marker="doc/reference_manual:code_loading#on_load">Running a
Function When a Module is Loaded</seealso> in the Erlang Reference
Manual) to load the NIF library automatically when the module is
@@ -135,27 +135,14 @@ ok
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 need to load its own NIF library (or maybe choose not
- to). The new code version can, however, choose to load the
- same NIF library as the old code if it wants to. Sharing the
- dynamic library means that static data defined by the library
- is shared as well. To avoid unintentionally shared static
- data, 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">
- <c>enif_priv_data</c></seealso>.</p>
-
- <p>A NIF library cannot be loaded explicitly. A library is
- automatically unloaded when the module code that it belongs to is purged
- by the code server.</p>
+ <p>Once loaded, a NIF library is persistent. It will not be unloaded
+ until the module code version that it belongs to is purged.</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. Functions exist
+ <p>All interaction between NIF code and the Erlang runtime system is
+ performed by calling NIF API functions. Functions exist
for the following functionality:</p>
<taglist>
@@ -286,6 +273,19 @@ return term;</code>
library is postponed as long as there exist resource objects with a
destructor function in the library.</p>
</item>
+ <tag>Module upgrade and static data</tag>
+ <item>
+ <p>A loaded NIF library is tied to the Erlang module instance
+ that loaded it. If the module is upgraded, the new module instance
+ needs to load its own NIF library (or maybe choose not to). The new
+ module instance can, however, choose to load the exact same NIF library
+ as the old code if it wants to. Sharing the dynamic library means that
+ static data defined by the library is shared as well. To avoid
+ unintentionally shared static data between module instances, each Erlang
+ module version can keep its own private data. This private data can be
+ set when the NIF library is loaded and later retrieved by calling
+ <seealso marker="#enif_priv_data"><c>enif_priv_data</c></seealso>.</p>
+ </item>
<tag>Threads and concurrency</tag>
<item>
<p>A NIF is thread-safe without any explicit synchronization as
@@ -296,8 +296,8 @@ return term;</code>
synchronization. This includes terms in process-independent
environments that are shared between threads. Resource objects 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>The library initialization callbacks <c>load</c> and
+ <c>upgrade</c> are thread-safe even for shared state data.</p>
</item>
<tag><marker id="version_management"/>Version Management</tag>
<item>
@@ -402,14 +402,14 @@ return term;</code>
<tag><marker id="dirty_nifs"/>Dirty NIF</tag>
<item>
<note>
- <p><em>The dirty NIF functionality described here
- is experimental</em>. Dirty NIF support is available only when
- the emulator is configured with dirty schedulers enabled. This
- feature is disabled by default. The Erlang runtime
- without SMP support does not support dirty schedulers even when
- the dirty scheduler support is enabled. To check at runtime for
- the presence of dirty scheduler threads, code can use the
- <seealso marker="#enif_system_info">
+ <p>Dirty NIF support is available only when the emulator is
+ configured with dirty scheduler support. As of ERTS version
+ 9.0, dirty scheduler support is enabled by default on the
+ runtime system with SMP support. The Erlang runtime without
+ SMP support does <em>not</em> support dirty schedulers even
+ when the dirty scheduler support is explicitly enabled. To
+ check at runtime for the presence of dirty scheduler threads,
+ code can use the <seealso marker="#enif_system_info">
<c>enif_system_info()</c></seealso> API function.</p>
</note>
<p>A NIF that cannot be split and cannot execute in a millisecond
@@ -498,7 +498,7 @@ return term;</code>
<title>Initialization</title>
<taglist>
<tag><marker id="ERL_NIF_INIT"/><c>ERL_NIF_INIT(MODULE,
- ErlNifFunc funcs[], load, reload, upgrade, unload)</c></tag>
+ ErlNifFunc funcs[], load, NULL, upgrade, unload)</c></tag>
<item>
<p>This is the magic macro to initialize a NIF library. It
is to be evaluated in global file scope.</p>
@@ -507,11 +507,14 @@ return term;</code>
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
+ <p><c>load</c>, <c>upgrade</c> and <c>unload</c>
+ are pointers to functions. One of <c>load</c> or
<c>upgrade</c> is called to initialize the library.
<c>unload</c> is called to release the library. All are
described individually below.</p>
+ <p>The fourth argument <c>NULL</c> is ignored. It
+ was earlier used for the deprectated <c>reload</c> callback
+ which is no longer supported since OTP 20.</p>
<p>If compiling a NIF for static inclusion through
<c>--enable-static-nifs</c>, you must define <c>STATIC_ERLANG_NIF</c>
before the <c>ERL_NIF_INIT</c> declaration.</p>
@@ -522,7 +525,7 @@ return term;</code>
<p><c>load</c> is called when the NIF library is loaded
and no previously loaded library exists for this module.</p>
<p><c>*priv_data</c> can be set to point to some private data
- that the library needs to keep a state between NIF
+ if the library needs to keep a state between NIF
calls. <c>enif_priv_data</c> returns this pointer.
<c>*priv_data</c> is initialized to <c>NULL</c> when <c>load</c> is
called.</p>
@@ -539,7 +542,7 @@ return term;</code>
and there is old code of this module with a loaded NIF library.</p>
<p>Works as <c>load</c>, except 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> is
+ <c>upgrade</c> for the old module code. <c>*priv_data</c> is
initialized to <c>NULL</c> when <c>upgrade</c> is called. It is
allowed to write to both <c>*priv_data</c> and
<c>*old_priv_data.</c></p>
@@ -551,27 +554,7 @@ return term;</code>
<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. Notice that <c>unload</c> is not
- called for a replaced library as a consequence of <c>reload</c>.</p>
- </item>
- <tag><marker id="reload"/><c>int (*reload)(ErlNifEnv* env, void**
- priv_data, ERL_NIF_TERM load_info)</c></tag>
- <item>
- <note>
- <p><em>The reload mechanism is deprecated.</em> It was only intended
- as a development feature. Do not use it as an upgrade method for
- live production systems. It can be removed in future releases.
- Ensure to pass <c>reload</c> as <c>NULL</c> to
- <seealso marker="#ERL_NIF_INIT"><c>ERL_NIF_INIT</c></seealso>
- to disable it when not used.</p>
- </note>
- <p><c>reload</c> is called when the NIF library is loaded and a
- previously loaded library already exists for this module code.</p>
- <p>Works as <c>load</c>, except 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 fails to load if <c>reload</c> returns
- anything other than <c>0</c> or if <c>reload</c> is <c>NULL</c>.</p>
+ module may or may not exist.</p>
</item>
</taglist>
</section>
@@ -659,9 +642,6 @@ typedef struct {
<p><c>flags</c> can be used to indicate that the NIF is a
<seealso marker="#dirty_nifs">dirty NIF</seealso> that is to be
executed on a dirty scheduler thread.</p>
- <p><em>The dirty NIF functionality described here is
- experimental.</em> You have to enable support for dirty
- schedulers when building OTP to try out the functionality.</p>
<p>If the dirty NIF is expected to be CPU-bound, its <c>flags</c>
field is to be set to <c>ERL_NIF_DIRTY_JOB_CPU_BOUND</c> or
<c>ERL_NIF_DIRTY_JOB_IO_BOUND</c>.</p>
@@ -695,6 +675,18 @@ typedef struct {
<p>When receiving data from untrusted sources, use option
<c>ERL_NIF_BIN2TERM_SAFE</c>.</p>
</item>
+ <tag><marker id="ErlNifMonitor"/><c>ErlNifMonitor</c></tag>
+ <item>
+ <p>This is an opaque data type that identifies a monitor.</p>
+ <p>The nif writer is to provide the memory for storing the
+ monitor when calling <seealso marker="#enif_monitor_process">
+ <c>enif_monitor_process</c></seealso>. The
+ address of the data is not stored by the runtime system, so
+ <c>ErlNifMonitor</c> can be used as any other data, it
+ can be copied, moved in memory, forgotten, and so on.
+ To compare two monitors, <seealso marker="#enif_compare_monitors">
+ <c>enif_compare_monitors</c></seealso> must be used.</p>
+ </item>
<tag><marker id="ErlNifPid"/><c>ErlNifPid</c></tag>
<item>
<p>A process identifier (pid). In contrast to pid terms (instances of
@@ -716,11 +708,46 @@ typedef struct {
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="ErlNifResourceTypeInit"/><c>ErlNifResourceTypeInit</c></tag>
+ <item>
+ <code type="none">
+typedef struct {
+ ErlNifResourceDtor* dtor;
+ ErlNifResourceStop* stop;
+} ErlNifResourceTypeInit;</code>
+ <p>Initialization structure read by <seealso marker="#enif_open_resource_type_x">
+ enif_open_resource_type_x</seealso>.</p>
+ </item>
<tag><marker id="ErlNifResourceDtor"/><c>ErlNifResourceDtor</c></tag>
<item>
<code type="none">
typedef void ErlNifResourceDtor(ErlNifEnv* env, void* obj);</code>
<p>The function prototype of a resource destructor function.</p>
+ <p>The <c>obj</c> argument is a pointer to the resource. The only
+ allowed use for the resource in the destructor is to access its
+ user data one final time. The destructor is guaranteed to be the
+ last callback before the resource is deallocated.</p>
+ </item>
+ <tag><marker id="ErlNifResourceDown"/><c>ErlNifResourceDown</c></tag>
+ <item>
+ <code type="none">
+typedef void ErlNifResourceDown(ErlNifEnv* env, void* obj, const ErlNifPid* pid, const ErlNifMonitor* mon);</code>
+ <p>The function prototype of a resource down function,
+ called on the behalf of <seealso marker="#enif_monitor_process">
+ enif_monitor_process</seealso>. <c>obj</c> is the resource, <c>pid</c>
+ is the identity of the monitored process that is exiting, and <c>mon</c>
+ is the identity of the monitor.
+ </p>
+ </item>
+ <tag><marker id="ErlNifResourceStop"/><c>ErlNifResourceStop</c></tag>
+ <item>
+ <code type="none">
+typedef void ErlNifResourceStop(ErlNifEnv* env, void* obj, ErlNifEvent event, int is_direct_call);</code>
+ <p>The function prototype of a resource stop function,
+ called on the behalf of <seealso marker="#enif_select">
+ enif_select</seealso>. <c>obj</c> is the resource, <c>event</c> is OS event,
+ <c>is_direct_call</c> is true if the call is made directly from <c>enif_select</c>
+ or false if it is a scheduled call (potentially from another thread).</p>
</item>
<tag><marker id="ErlNifCharEncoding"/><c>ErlNifCharEncoding</c></tag>
<item>
@@ -786,6 +813,29 @@ typedef enum {
</item>
</taglist>
</item>
+ <tag><marker id="ErlNifHash"/><c>ErlNifHash</c></tag>
+ <item>
+ <p>An enumeration of the supported hash types that can be generated
+ using <seealso marker="#enif_hash"><c>enif_hash</c></seealso>.
+ </p>
+ <taglist>
+ <tag><c>ERL_NIF_INTERNAL_HASH</c></tag>
+ <item>
+ <p>Non-portable hash function that only guarantees the same hash
+ for the same term within one Erlang VM instance.</p>
+ <p>It takes 32-bit salt values and generates hashes within <c>0..2^32-1</c>.</p>
+ </item>
+ <tag><c>ERL_NIF_PHASH2</c></tag>
+ <item>
+ <p>Portable hash function that gives the same hash for the
+ same Erlang term regardless of machine architecture and ERTS version.</p>
+ <p><em>It ignores salt values</em> and generates hashes within <c>0..2^27-1</c>.</p>
+ <p>Slower than <c>ERL_NIF_INTERNAL_HASH.</c>
+ It corresponds to <seealso marker="erlang#phash2-1"><c>erlang:phash2/1</c></seealso>.
+ </p>
+ </item>
+ </taglist>
+ </item>
</taglist>
</section>
@@ -895,6 +945,21 @@ typedef enum {
</func>
<func>
+ <name><ret>int</ret><nametext>enif_compare_monitors(const ErlNifMonitor
+ *monitor1, const ErlNifMonitor *monitor2)</nametext></name>
+ <fsummary>Compare two monitors.</fsummary>
+ <desc>
+ <marker id="enif_compare_monitors"></marker>
+ <p>Compares two <seealso marker="#ErlNifMonitor"><c>ErlNifMonitor</c></seealso>s.
+ Can also be used to imply some artificial order on monitors,
+ for whatever reason.</p>
+ <p>Returns <c>0</c> if <c>monitor1</c> and <c>monitor2</c> are equal,
+ &lt; <c>0</c> if <c>monitor1</c> &lt; <c>monitor2</c>, and
+ &gt; <c>0</c> if <c>monitor1</c> &gt; <c>monitor2</c>.</p>
+ </desc>
+ </func>
+
+ <func>
<name><ret>void</ret>
<nametext>enif_cond_broadcast(ErlNifCond *cnd)</nametext></name>
<fsummary></fsummary>
@@ -1022,6 +1087,30 @@ typedef enum {
</func>
<func>
+ <name><ret>int</ret><nametext>enif_demonitor_process(ErlNifEnv* env, void* obj,
+ const ErlNifMonitor* mon)</nametext></name>
+ <fsummary>Cancel a process monitor.</fsummary>
+ <desc>
+ <marker id="enif_demonitor_process"></marker>
+ <p>Cancels a monitor created earlier with <seealso marker="#enif_monitor_process">
+ <c>enif_monitor_process</c></seealso>. Argument <c>obj</c> is a pointer
+ to the resource holding the monitor and <c>*mon</c> identifies the monitor.</p>
+ <p>Returns <c>0</c> if the monitor was successfully identified and removed.
+ Returns a non-zero value if the monitor could not be identified, which means
+ it was either</p>
+ <list type="bulleted">
+ <item>never created for this resource</item>
+ <item>already cancelled</item>
+ <item>already triggered</item>
+ <item>just about to be triggered by a concurrent thread</item>
+ </list>
+ <p>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.</p>
+ </desc>
+ </func>
+
+ <func>
<name><ret>int</ret>
<nametext>enif_equal_tids(ErlNifTid tid1, ErlNifTid tid2)</nametext>
</name>
@@ -1321,6 +1410,19 @@ typedef enum {
</func>
<func>
+ <name>
+ <ret>ErlNifUInt64</ret>
+ <nametext>enif_hash(ErlNifHash type, ERL_NIF_TERM term, ErlNifUInt64 salt)</nametext>
+ </name>
+ <fsummary>Hash terms.</fsummary>
+ <desc>
+ <p>Hashes <c>term</c> according to the specified
+ <seealso marker="#ErlNifHash"><c>ErlNifHash</c></seealso> <c>type</c>.</p>
+ <p>Ranges of taken salt (if any) and returned value depend on the hash type.</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>
@@ -2137,6 +2239,36 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
</func>
<func>
+ <name><ret>int</ret><nametext>enif_monitor_process(ErlNifEnv* env, void* obj,
+ const ErlNifPid* target_pid, ErlNifMonitor* mon)</nametext></name>
+ <fsummary>Monitor a process from a resource.</fsummary>
+ <desc>
+ <marker id="enif_monitor_process"></marker>
+ <p>Starts monitoring a process from a resource. When a process is
+ monitored, a process exit results in a call to the provided
+ <seealso marker="#ErlNifResourceDown">
+ <c>down</c></seealso> callback associated with the resource type.</p>
+ <p>Argument <c>obj</c> is pointer to the resource to hold the monitor and
+ <c>*target_pid</c> identifies the local process to be monitored.</p>
+ <p>If <c>mon</c> is not <c>NULL</c>, a successful call stores the
+ identity of the monitor in the
+ <seealso marker="#ErlNifMonitor"><c>ErlNifMonitor</c></seealso>
+ struct pointed to by <c>mon</c>. This identifier is used to refer to the
+ monitor for later removal with
+ <seealso marker="#enif_demonitor_process"><c>enif_demonitor_process</c></seealso>
+ or compare with
+ <seealso marker="#enif_compare_monitors"><c>enif_compare_monitors</c></seealso>.
+ A monitor is automatically removed when it triggers or when
+ the resource is deallocated.</p>
+ <p>Returns <c>0</c> on success, &lt; 0 if no <c>down</c> callback is
+ provided, and &gt; 0 if the process is no longer alive.</p>
+ <p>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.</p>
+ </desc>
+ </func>
+
+ <func>
<name><ret>ErlNifTime</ret>
<nametext>enif_monotonic_time(ErlNifTimeUnit time_unit)</nametext>
</name>
@@ -2249,14 +2381,31 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
returns <c>NULL</c> and sets <c>*tried</c> to <c>flags</c>.
It is allowed to set <c>tried</c> to <c>NULL</c>.</p>
<p>Notice that <c>enif_open_resource_type</c> is only allowed to be
- called in the three callbacks
- <seealso marker="#load"><c>load</c></seealso>,
- <seealso marker="#reload"><c>reload</c></seealso>, and
+ called in the two callbacks
+ <seealso marker="#load"><c>load</c></seealso> and
<seealso marker="#upgrade"><c>upgrade</c></seealso>.</p>
</desc>
</func>
<func>
+ <name><ret>ErlNifResourceType *</ret>
+ <nametext>enif_open_resource_type_x(ErlNifEnv* env, const char* name,
+ ErlNifResourceTypeInit* init,
+ ErlNifResourceFlags flags, ErlNifResourceFlags* tried)</nametext>
+ </name>
+ <fsummary>Create or takeover a resource type.</fsummary>
+ <desc>
+ <p>Same as <seealso marker="#enif_open_resource_type"><c>enif_open_resource_type</c></seealso>
+ except is also accept a <c>stop</c> callback for resource types that are
+ used together with <seealso marker="#enif_select"><c>enif_select</c></seealso>.</p>
+ <p>Argument <c>init</c> is a pointer to an
+ <seealso marker="#ErlNifResourceTypeInit"><c>ErlNifResourceTypeInit</c></seealso>
+ structure that contains the function pointers for destructor, down and stop callbacks
+ for the resource type.</p>
+ </desc>
+ </func>
+
+ <func>
<name><ret>int</ret><nametext>enif_port_command(ErlNifEnv* env, const
ErlNifPort* to_port, ErlNifEnv *msg_env, ERL_NIF_TERM msg)</nametext>
</name>
@@ -2305,10 +2454,8 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
<fsummary>Get the private data of a NIF library.</fsummary>
<desc>
<p>Returns the pointer to the private data that was set by
- <seealso marker="#load"><c>load</c></seealso>,
- <seealso marker="#reload"><c>reload</c></seealso>, or
+ <seealso marker="#load"><c>load</c></seealso> or
<seealso marker="#upgrade"><c>upgrade</c></seealso>.</p>
- <p>Was previously named <c>enif_get_data</c>.</p>
</desc>
</func>
@@ -2365,7 +2512,7 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
<nametext>enif_release_resource(void* obj)</nametext></name>
<fsummary>Release a resource object.</fsummary>
<desc>
- <p>Removes a reference to resource object <c>obj</c>obtained from
+ <p>Removes a reference to resource object <c>obj</c> obtained from
<seealso marker="#enif_alloc_resource">
<c>enif_alloc_resource</c></seealso>.
The resource object is destructed when the last reference is removed.
@@ -2470,9 +2617,6 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
application to break up long-running work into multiple regular NIF
calls or to schedule a <seealso marker="#dirty_nifs">
dirty NIF</seealso> to execute on a dirty scheduler thread.</p>
- <p><em>The dirty NIF functionality described here is
- experimental.</em> You have to enable support for dirty
- schedulers when building OTP to try out the functionality.</p>
<taglist>
<tag><c>fun_name</c></tag>
<item>
@@ -2483,13 +2627,13 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
<tag><c>flags</c></tag>
<item>
<p>Must be set to <c>0</c> for a regular NIF. If the emulator was
- built with the experimental dirty scheduler support enabled,
+ built with dirty scheduler support enabled,
<c>flags</c> can be set to either
<c>ERL_NIF_DIRTY_JOB_CPU_BOUND</c> if the job is expected to be
CPU-bound, or <c>ERL_NIF_DIRTY_JOB_IO_BOUND</c> for
jobs that will be I/O-bound. If dirty scheduler threads are not
available in the emulator, an attempt to schedule such a job
- results in a <c>badarg</c> exception.</p>
+ results in a <c>notsup</c> exception.</p>
</item>
<tag><c>argc</c> and <c>argv</c></tag>
<item>
@@ -2508,6 +2652,85 @@ enif_map_iterator_destroy(env, &amp;iter);</code>
</func>
<func>
+ <name><ret>int</ret>
+ <nametext>enif_select(ErlNifEnv* env, ErlNifEvent event, enum ErlNifSelectFlags mode,
+ void* obj, const ErlNifPid* pid, ERL_NIF_TERM ref)</nametext>
+ </name>
+ <fsummary>Manage subscription on IO event.</fsummary>
+ <desc>
+ <p>This function can be used to receive asynchronous notifications
+ when OS-specific event objects become ready for either read or write operations.</p>
+ <p>Argument <c>event</c> identifies the event object. On Unix
+ systems, the functions <c>select</c>/<c>poll</c> are used. The event
+ object must be a socket, pipe or other file descriptor object that
+ <c>select</c>/<c>poll</c> can use.</p>
+ <p>Argument <c>mode</c> describes the type of events to wait for. It can be
+ <c>ERL_NIF_SELECT_READ</c>, <c>ERL_NIF_SELECT_WRITE</c> or a bitwise
+ OR combination to wait for both. It can also be <c>ERL_NIF_SELECT_STOP</c>
+ which is described further below. When a read or write event is triggerred,
+ a notification message like this is sent to the process identified by
+ <c>pid</c>:</p>
+ <code type="none">{select, Obj, Ref, ready_input | ready_output}</code>
+ <p><c>ready_input</c> or <c>ready_output</c> indicates if the event object
+ is ready for reading or writing.</p>
+ <p>Argument <c>pid</c> may be <c>NULL</c> to indicate the calling process.</p>
+ <p>Argument <c>obj</c> is a resource object obtained from
+ <seealso marker="#enif_alloc_resource"><c>enif_alloc_resource</c></seealso>.
+ The purpose of the resource objects is as a container of the event object
+ to manage its state and lifetime. A handle to the resource is received
+ in the notification message as <c>Obj</c>.</p>
+ <p>Argument <c>ref</c> must be either a reference obtained from
+ <seealso marker="erlang#make_ref-0"><c>erlang:make_ref/0</c></seealso>
+ or the atom <c>undefined</c>. It will be passed as <c>Ref</c> in the notifications.
+ If a selective <c>receive</c> statement is used to wait for the notification
+ then a reference created just before the <c>receive</c> will exploit a runtime
+ optimization that bypasses all earlier received messages in the queue.</p>
+ <p>The notifications are one-shot only. To receive further notifications of the same
+ type (read or write), repeated calls to <c>enif_select</c> must be made
+ after receiving each notification.</p>
+ <p>Use <c>ERL_NIF_SELECT_STOP</c> as <c>mode</c> in order to safely
+ close an event object that has been passed to <c>enif_select</c>. The
+ <seealso marker="#ErlNifResourceStop"><c>stop</c></seealso> callback
+ of the resource <c>obj</c> will be called when it is safe to close
+ the event object. This safe way of closing event objects must be used
+ even if all notifications have been received and no further calls to
+ <c>enif_select</c> have been made.</p>
+ <p>Returns a non-negative value on success where the following bits can be set:</p>
+ <taglist>
+ <tag><c>ERL_NIF_SELECT_STOP_CALLED</c></tag>
+ <item>The stop callback was called directly by <c>enif_select</c>.</item>
+ <tag><c>ERL_NIF_SELECT_STOP_SCHEDULED</c></tag>
+ <item>The stop callback was scheduled to run on some other thread
+ or later by this thread.</item>
+ </taglist>
+ <p>Returns a negative value if the call failed where the follwing bits can be set:</p>
+ <taglist>
+ <tag><c>ERL_NIF_SELECT_INVALID_EVENT</c></tag>
+ <item>Argument <c>event</c> is not a valid OS event object.</item>
+ <tag><c>ERL_NIF_SELECT_FAILED</c></tag>
+ <item>The system call failed to add the event object to the poll set.</item>
+ </taglist>
+ <note>
+ <p>Use bitwise AND to test for specific bits in the return vaue.
+ New significant bits may be added in future releases to give more detailed
+ information for both failed and successful calls. Do NOT use equallity tests
+ like <c>==</c>, as that may cause your application to stop working.</p>
+ <p>Example:</p>
+ <code type="none">
+retval = enif_select(env, fd, ERL_NIF_SELECT_STOP, resource, ref);
+if (retval &lt; 0) {
+ /* handle error */
+}
+/* Success! */
+if (retval &amp; ERL_NIF_SELECT_STOP_CALLED) {
+ /* ... */
+}
+</code>
+ </note>
+ </desc>
+ </func>
+
+ <func>
<name><ret>ErlNifPid *</ret>
<nametext>enif_self(ErlNifEnv* caller_env, ErlNifPid* pid)</nametext>
</name>