php-doc-en/reference/sem/functions/shm-attach.xml

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<refentry xmlns="http://docbook.org/ns/docbook" xml:id="function.shm-attach">
 <refnamediv>
  <refname>shm_attach</refname>
  <refpurpose>Creates or open a shared memory segment</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>resource</type><methodname>shm_attach</methodname>
   <methodparam><type>int</type><parameter>key</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>memsize</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>perm</parameter><initializer>0666</initializer></methodparam>
  </methodsynopsis>
  <para>
   <function>shm_attach</function> returns an id that can be used to access
   the System V shared memory with the given <parameter>key</parameter>, the
   first call creates the shared memory segment with 
   <parameter>memsize</parameter> and the optional perm-bits 
   <parameter>perm</parameter>.
  </para>
  <para>
   A second call to <function>shm_attach</function> for the same
   <parameter>key</parameter> will return a different shared memory
   identifier, but both identifiers access the same underlying
   shared memory. <parameter>memsize</parameter> and
   <parameter>perm</parameter> will be ignored.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>key</parameter></term>
     <listitem>
      <para>
       A numeric shared memory segment ID
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>memsize</parameter></term>
     <listitem>
      <para>
       The memory size. If not provided, default to the
       <literal>sysvshm.init_mem</literal> in the &php.ini;, otherwise 10000
       bytes.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>perm</parameter></term>
     <listitem>
      <para>
       The optional permission bits. Default to 0666.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns a shared memory segment identifier.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>5.3.0</entry>
       <entry>
         This function now returns a &resource; instead of an 
         <link linkend="language.types.integer">integer</link>.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <note>
   <para>
    This function used to return an integer value prior to 
    PHP 5.3.0. To achieve the same value in a portable manner, the 
    return value can be cast to an integer like:
   </para>
   <para>
    <example>
     <programlisting role="php">
<![CDATA[
<?php
// Create a temporary file and return its path
$tmp = tempnam('/tmp', 'PHP');

// Get the file token key
$key = ftok($tmp, 'a');

// Attach the SHM resource, notice the cast afterwards
$id = shm_attach($key);

if ($id === false) {
    die('Unable to create the shared memory segment');
}

// Cast to integer, since prior to PHP 5.3.0 the resource id 
// is returned which can be exposed when casting a resource
// to an integer
$id = (integer) $id;
?>
]]>
     </programlisting>
    </example>
   </para>
  </note>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>shm_detach</function></member>
    <member><function>ftok</function></member>
   </simplelist>
  </para>
 </refsect1>  

</refentry>

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