shmop_open
Create or open shared memory block
Description
Shmopfalse shmop_open(
int $key,
string $mode,
int $permissions,
int $size
)
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.
Errors/Exceptions
If mode is invalid, or size is less than or equal to zero,
a ValueError is thrown.
On other failures, E_WARNING is emitted.
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.