shmop_open
(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)
shmop_open — Create or open shared memory block
Description
shmop_open() can create or open a shared memory block.
Parameters
-
key -
System's id for the shared memory block. Can be passed as a decimal or hex.
-
mode -
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.
-
permissions -
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, like for example
0644 -
size -
The 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.
Return Values
On success shmop_open() will return a Shmop instance that you can
use to access the shared memory segment you've created. false is
returned on failure.
Changelog
| Version | Description |
|---|---|
| 8.0.0 | On success, this function returns an Shmop instance now; previously, a resource was returned. |
Examples
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().
