shmop_open
(PHP 4 >= 4.0.4)
shmop_open -- Create or open shared memory block
Description
int shmop_open ( int key, string flags, int mode, int size)
shmop_open() can create or open a shared memory block.
shmop_open() takes 4 parameters: key, which is the system's
id for the shared memory block, this parameter can be passed
as a decimal or hex. The second parameter are the flags
that you can use:
"a" for access (sets SHM_RDONLY for shmat) use
this flag when you need to open an existing shared memory
segment for read only
"c" for create (sets IPC_CREATE) use this flag
when you need to create a new shared memory segment or if
a segment with the same key exists, try to open it for read
and write
"w" for read & write access use this flag
when you need to read and write to a shared memory segment,
use this flag in most cases.
"n" create a new memory segment (sets IPC_CREATE|IPC_EXCL)
use this flag when you want to create a new shared memory
segment but if one already exists with the same flag, fail.
This is useful for security purposes, using this you can
prevent race condition exploits.
The third parameter is the mode, which are the permissions
that you wish to assign to your memory segment, those are
the same as permission for a file. Permissions need to be
passed in octal form ex. 0644. The last parameter is size
of the shared memory block you wish to create in bytes.
Note: Note: the 3rd and 4th should be entered as 0 if you
are opening an existing memory segment. On success shmop_open()
will return an id that you can use to access the shared
memory segment you've created.
Example 1. Create a new shared memory block
<?php
$shm_key = ftok(__FILE__, 't');
$shm_id = shmop_open($shm_key, "c", 0644, 100);
?>
This example opened a shared memory block with a system
id returned by ftok().
