Semaphore Functions
PHP Manual

shm_attach

Creates or open a shared memory segment

Description

resource shm_attach ( int $key [, int $memsize [, int $perm = 0666 ]] )

shm_attach returns an id that can be used to access the System V shared memory with the given key, the first call creates the shared memory segment with memsize and the optional perm-bits perm.

A second call to shm_attach for the same key will return a different shared memory identifier, but both identifiers access the same underlying shared memory. memsize and perm will be ignored.

Parameters

key

A numeric shared memory segment ID

memsize

The memory size. If not provided, default to the sysvshm.init_mem in the php.ini, otherwise 10000 bytes.

perm

The optional permission bits. Default to 0666.

Return Values

Returns a shared memory segment identifier.

Changelog

Version Description
5.3.0 This function now returns a resource instead of an integer.

Notes

Note:

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:

<?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;
?>

See Also

  • shm_detach
  • ftok