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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.pcntl-waitid" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>pcntl_waitid</refname>
<refpurpose>Waits for a child process to change state</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>bool</type><methodname>pcntl_waitid</methodname>
<methodparam choice="opt"><type>int</type><parameter>idtype</parameter><initializer><constant>P_ALL</constant></initializer></methodparam>
<methodparam choice="opt"><type class="union"><type>int</type><type>null</type></type><parameter>id</parameter><initializer>&null;</initializer></methodparam>
<methodparam choice="opt"><type>array</type><parameter role="reference">info</parameter><initializer>[]</initializer></methodparam>
<methodparam choice="opt"><type>int</type><parameter>flags</parameter><initializer><constant>WEXITED</constant></initializer></methodparam>
</methodsynopsis>
<para>
Obtains status information pertaining to termination, stop, and/or continue
events in one of the caller's child processes.
</para>
<para>
Unless <constant>WNOHANG</constant> flag is passed, the calling process will
become blocked until an error occurs, or status information becomes
available that satisfies all of the following:
<itemizedlist>
<listitem>
<simpara>
The status information is from one of the child processes in the set of
child processes specified by the <parameter>idtype</parameter> and
<parameter>id</parameter> arguments.
</simpara>
</listitem>
<listitem>
<simpara>
The state change in the status information matches one of the state change
flags set in the <parameter>flags</parameter> argument.
</simpara>
</listitem>
</itemizedlist>
</para>
<para>
If matching status information is available prior to the call to
<function>pcntl_waitid</function>, return shall be immediate. If matching
status information is available for two or more child processes, the order
in which their status is reported is unspecified.
</para>
<note>
<para>
This documentation covers the POSIX specification of the
<literal>waitid</literal> function, along with some additional parameters
specific to implementations on Linux, NetBSD and FreeBSD. Please see your
system's <literal>waitid(2)</literal> man page for specific details as to
how <literal>waitid</literal> works on your system.
</para>
</note>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<variablelist>
<varlistentry>
<term><parameter>idtype</parameter></term>
<term><parameter>id</parameter></term>
<listitem>
<simpara>
The <parameter>idtype</parameter> and <parameter>id</parameter> arguments
are used to specify which children to wait for.
</simpara>
<table>
<title>POSIX standard <parameter>idtype</parameter> and <parameter>id</parameter> arguments</title>
<tgroup cols="2">
<tbody>
<row>
<entry>If <parameter>idtype</parameter> is <literal>P_ALL</literal></entry>
<entry>
wait for any child process, <parameter>id</parameter> is ignored.
</entry>
</row>
<row>
<entry>If <parameter>idtype</parameter> is <literal>P_PID</literal></entry>
<entry>
wait for the child with process ID equal to <parameter>id</parameter>.
</entry>
</row>
<row>
<entry>If <parameter>idtype</parameter> is <literal>P_PGID</literal></entry>
<entry>
wait for any child with process group ID equal to <parameter>id</parameter>.
</entry>
</row>
</tbody>
</tgroup>
</table>
<table>
<title>Linux specific <parameter>idtype</parameter> and <parameter>id</parameter> arguments</title>
<tgroup cols="2">
<tbody>
<row>
<entry>If <parameter>idtype</parameter> is <literal>P_PIDFD</literal> (since Linux 5.4)</entry>
<entry>
wait for the child referred to by the PID file descriptor specified in
<parameter>id</parameter>.
(See the Linux <literal>pidfd_open(2)</literal> man page for further
information on PID file descriptors.)
</entry>
</row>
</tbody>
</tgroup>
</table>
<table>
<title>NetBSD and FreeBSD specific <parameter>idtype</parameter> and <parameter>id</parameter> arguments</title>
<tgroup cols="2">
<tbody>
<row>
<entry>
If <parameter>idtype</parameter> is <literal>P_UID</literal>
</entry>
<entry>
wait for processes whose effective user ID is equal to
<parameter>id</parameter>.
</entry>
</row>
<row>
<entry>
If <parameter>idtype</parameter> is <literal>P_GID</literal>
</entry>
<entry>
wait for processes whose effective group ID is equal to
<parameter>id</parameter>.
</entry>
</row>
<row>
<entry>
If <parameter>idtype</parameter> is <literal>P_SID</literal>
</entry>
<entry>
wait for processes whose session ID is equal to
<parameter>id</parameter>.
If the child process started its own session, its session ID will be
the same as its process ID. Otherwise the session ID of a child
process will match the caller's session ID.
</entry>
</row>
</tbody>
</tgroup>
</table>
<table>
<title>FreeBSD specific <parameter>idtype</parameter> and <parameter>id</parameter> arguments</title>
<tgroup cols="2">
<tbody>
<row>
<entry>
If <parameter>idtype</parameter> is <literal>P_JAILID</literal>
</entry>
<entry>
wait for processes within a jail whose jail identifier is equal to
<parameter>id</parameter>.
</entry>
</row>
</tbody>
</tgroup>
</table>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>info</parameter></term>
<listitem>
<para>
The <parameter>info</parameter> parameter is set to an array
containing information about the signal.
</para>
<para>
<parameter>info</parameter> array may contain the following keys:
<simplelist>
<member><literal>signo</literal>: Signal number</member>
<member><literal>errno</literal>: System error number</member>
<member><literal>code</literal>: Signal code</member>
<member><literal>status</literal>: Exit value or signal</member>
<member><literal>pid</literal>: Sending process ID</member>
<member><literal>uid</literal>: Real user ID of sending process</member>
<member><literal>utime</literal>: User time consumed</member>
<member><literal>stime</literal>: System time consumed</member>
</simplelist>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>flags</parameter></term>
<listitem>
<para>
The value of <parameter>flags</parameter> is the value of zero or more of
the following constants OR'ed together:
<table>
<title>possible values for <parameter>flags</parameter></title>
<tgroup cols="2">
<tbody>
<row>
<entry><constant>WCONTINUED</constant></entry>
<entry>
Status shall be returned for any continued child process whose
status either has not been reported since it continued from a job
control stop or has been reported only by calls to
<function>pcntl_waitid</function> with the
<constant>WNOWAIT</constant> flag set.
</entry>
</row>
<row>
<entry><constant>WEXITED</constant></entry>
<entry>
Wait for processes that have exited.
</entry>
</row>
<row>
<entry><constant>WNOHANG</constant></entry>
<entry>
Do not hang if no status is available; return immediately.
</entry>
</row>
<row>
<entry><constant>WNOWAIT</constant></entry>
<entry>
Keep the process whose status is returned in
<parameter>info</parameter> in a waitable state. This shall not
affect the state of the process; the process may be waited for again
after this call completes.
</entry>
</row>
<row>
<entry><constant>WSTOPPED</constant></entry>
<entry>
Status shall be returned for any child that has stopped upon receipt
of a signal, and whose status either has not been reported since it
stopped or has been reported only by calls to
<function>pcntl_waitid</function> with the
<constant>WNOWAIT</constant> flag set.
</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
<function>pcntl_waitid</function> returns &true; if
<constant>WNOHANG</constant> was specified and status is not available for
any process specified by <parameter>idtype</parameter> and
<parameter>id</parameter>.
</para>
<para>
<function>pcntl_waitid</function> returns &true; due to the change of state
of one of its children.
</para>
<para>
Otherwise, &false; is returned and <function>pcntl_get_last_error</function>
can be used to get the <literal>errno</literal> error number.
</para>
<note>
<para>
Once an <literal>errno</literal> error number has been obtained,
<function>pcntl_strerror</function> can be used to get the text message
associated with it.
</para>
</note>
</refsect1>
<refsect1 role="errors">
&reftitle.errors;
<table>
<title>Error number (<literal>errno</literal>) values</title>
<tgroup cols="2">
<tbody>
<row>
<entry><constant>ECHILD</constant></entry>
<entry>
The calling process has no existing unwaited-for child processes.
</entry>
</row>
<row>
<entry><constant>EINTR</constant></entry>
<entry>
<function>pcntl_waitid</function> was interrupted by a signal.
</entry>
</row>
<row>
<entry><constant>EINVAL</constant></entry>
<entry>
An invalid value was specified for <parameter>flags</parameter>, or
<parameter>idtype</parameter> and <parameter>id</parameter> specify an
invalid set of processes.
</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>pcntl_waitpid</function></member>
<member><function>pcntl_wait</function></member>
<member><function>pcntl_fork</function></member>
<member><function>pcntl_signal</function></member>
<member><function>pcntl_wifexited</function></member>
<member><function>pcntl_wifstopped</function></member>
<member><function>pcntl_wifsignaled</function></member>
<member><function>pcntl_wexitstatus</function></member>
<member><function>pcntl_wtermsig</function></member>
<member><function>pcntl_wstopsig</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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