shm_attach

(PHP 4, PHP 5, PHP 7, PHP 8)

shm_attach — Creates or open a shared memory segment

Description

shm_attach(int $key, ?int $size = null, int $permissions = 0666): SysvSharedMemory|false

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 size and the optional perm-bits permissions.

A second call to shm_attach() for the same key will return a different SysvSharedMemory instance, but both instances access the same underlying shared memory. size and permissions will be ignored.

Parameters

key
A numeric shared memory segment ID
size
The memory size. If not provided, default to the sysvshm.init_mem in the php.ini, otherwise 10000 bytes.
permissions
The optional permission bits. Default to 0666.

Return Values

Returns a SysvSharedMemory instance on success, or false on failure.

Changelog

VersionDescription
8.0.0On success, this function returns an SysvSharedMemory instance now; previously, a resource was returned.
8.0.0size is nullable now.

See Also

  • shm_detach() - Disconnects from shared memory segment
  • ftok() - Convert a pathname and a project identifier to a System V IPC key