php-doc-en/reference/pcntl/functions/pcntl-waitpid.xml

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<refentry xml:id="function.pcntl-waitpid" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>pcntl_waitpid</refname>
  <refpurpose>Waits on or returns the status of a forked child</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>int</type><methodname>pcntl_waitpid</methodname>
   <methodparam><type>int</type><parameter>process_id</parameter></methodparam>
   <methodparam><type>int</type><parameter role="reference">status</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>flags</parameter><initializer>0</initializer></methodparam>
   <methodparam choice="opt"><type>array</type><parameter role="reference">resource_usage</parameter><initializer>[]</initializer></methodparam>
  </methodsynopsis>
  <para>
   Suspends execution of the current process until a child as specified by
   the <parameter>process_id</parameter> argument has exited, or until a signal is
   delivered whose action is to terminate the current process or to call a
   signal handling function.
  </para>
  <para>
   If a child as requested by <parameter>process_id</parameter> has already exited
   by the time of the call (a so-called "zombie" process), the function
   returns immediately.  Any system resources used by the child are freed.
   Please see your system's waitpid(2) man page for specific details as to
   how waitpid works on your system.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>process_id</parameter></term>
     <listitem>
      <para>
       The value of <parameter>process_id</parameter> can be one of the following:
       <table>
        <title>possible values for <parameter>process_id</parameter></title>
        <tgroup cols="2">
         <tbody>
          <row>
           <entry><literal>&lt; -1</literal></entry>
           <entry>
            wait for any child process whose process group ID is equal to
            the absolute value of <parameter>process_id</parameter>.
           </entry>
          </row>
          <row>
           <entry><literal>-1</literal></entry>
           <entry>
            wait for any child process; this is the same behaviour that
            the wait function exhibits.
           </entry>
          </row>
          <row>
           <entry><literal>0</literal></entry>
           <entry>
            wait for any child process whose process group ID is equal to
            that of the calling process.
           </entry>
          </row>
          <row>
           <entry><literal>&gt; 0</literal></entry>
           <entry>
            wait for the child whose process ID is equal to the value of
            <parameter>process_id</parameter>.
           </entry>
          </row>
         </tbody>
        </tgroup>
       </table>
      </para>
      <note>
       <para>
        Specifying <literal>-1</literal> as the <parameter>process_id</parameter> is
        equivalent to the functionality <function>pcntl_wait</function> provides
        (minus <parameter>flags</parameter>).
       </para>
      </note>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>status</parameter></term>
     <listitem>
      <para>
       <function>pcntl_waitpid</function> will store status information
       in the <parameter>status</parameter> parameter which can be
       evaluated using the following functions:
       <function>pcntl_wifexited</function>,
       <function>pcntl_wifstopped</function>,
       <function>pcntl_wifsignaled</function>,
       <function>pcntl_wexitstatus</function>,
       <function>pcntl_wtermsig</function> and
       <function>pcntl_wstopsig</function>.
      </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 two global constants
       <literal>OR</literal>'ed together:
       <table>
        <title>possible values for <parameter>flags</parameter></title>
        <tgroup cols="2">
         <tbody>
          <row>
           <entry><literal>WNOHANG</literal></entry>
           <entry>
            return immediately if no child has exited.
           </entry>
          </row>
          <row>
           <entry><literal>WUNTRACED</literal></entry>
           <entry>
            return for children which are stopped, and whose status has
            not been reported.
           </entry>
          </row>
         </tbody>
        </tgroup>
       </table>
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   <function>pcntl_waitpid</function> returns the process ID of the
   child which exited, -1 on error or zero if <constant>WNOHANG</constant> was used and no
   child was available
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <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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