shm_attach
(PHP 4, PHP 5)
shm_attach — Creates or open a shared memory segment
Description
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.
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() - Disconnects from shared memory segment
- ftok() - Convert a pathname and a project identifier to a System V IPC key