XC. Semaphore, Shared Memory and IPC Functions


This module provides wrappers for the System V IPC family of functions. It includes semaphores, shared memory and inter-process messaging (IPC).

Semaphores may be used to provide exclusive access to resources on the current machine, or to limit the number of processes that may simultaneously use a resource.

This module provides also shared memory functions using System V shared memory. Shared memory may be used to provide access to global variables. Different httpd-daemons and even other programs (such as Perl, C, ...) are able to access this data to provide a global data-exchange. Remember, that shared memory is NOT safe against simultaneous access. Use semaphores for synchronization.

Táblázat 1. Limits of Shared Memory by the Unix OS

SHMMAXmax size of shared memory, normally 131072 bytes
SHMMINminimum size of shared memory, normally 1 byte
SHMMNI max amount of shared memory segments on a system, normally 100
SHMSEG max amount of shared memory segments per process, normally 6

The messaging functions may be used to send and receive messages to/from other processes. They provide a simple and effective means of exchanging data between processes, without the need for setting up an alternative using unix domain sockets.

Megjegyzés: These functions do not work on Windows systems.


Az itt leírt függvények a standard modulban találhatóak, ami mindig rendelkezésre áll.


Support for this functions are not enabled by default. To ennable System V semaphore support compile PHP with the option --enable-sysvsem. To enable the System V shared memory support compile PHP with the option --enable-sysvshm.

Futásidejű beállítások

Ez a kiterjesztés semmilyen konfigurációs beállításokat nem definiál.

Erőforrás típusok

Előre definiált állandók

Ez a kiterjesztés semmilyen konstans értéket nem definiál.

ftok --  Convert a pathname and a project identifier to a System V IPC key
msg_get_queue --  Create or attach to a message queue
msg_receive --  Receive a message from a message queue
msg_remove_queue --  Destroy a message queue
msg_send --  Send a message to a message queue
msg_set_queue --  Set information in the message queue data structure
msg_stat_queue --  Returns information from the message queue data structure
sem_acquire -- Acquire a semaphore
sem_get -- Get a semaphore id
sem_release -- Release a semaphore
sem_remove -- Remove a semaphore
shm_attach -- Creates or open a shared memory segment
shm_detach -- Disconnects from shared memory segment
shm_get_var -- Returns a variable from shared memory
shm_put_var -- Inserts or updates a variable in shared memory
shm_remove_var -- Removes a variable from shared memory
shm_remove -- Removes shared memory from Unix systems