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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.

Limits of Shared Memory by the Unix OS
SHMMAX max size of shared memory, normally 131072 bytes
SHMMIN minimum 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.

Notă: Această extensie nu este disponibilă pe platformele Windows.


Nu sunt necesare biblioteci externe pentru a asambla această extensie.


Support for this functions are not enabled by default. To enable 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. To enable the System V messages support compile PHP with the option --enable-sysvmsg.

Configuraţia la rulare

Comportamentul acestor funcţii este afectat de parametrii stabiliţi în php.ini.

Semaphore Configuration Options
Name Default Changeable Changelog
sysvmsg.value "42" PHP_INI_ALL  
sysvmsg.string "foobar" PHP_INI_ALL  
Pentru mai multe detalii şi definiţii ale constantelor PHP_INI_* accesaţi php.ini directives.

Tipurile resurselor

Constante predefinite

Constantele de mai jos sunt definite de această extensie şi vor fi disponibile doar dacă această extensie a fost compilată în interiorul PHP, sau a fost încărcată dinamic în timpul rulării.

System V message constants
Constant Type Changelog
MSG_IPC_NOWAIT integer  
MSG_EAGAIN integer  
MSG_EAGAIN integer As of 5.2.0
MSG_ENOMSG integer As of 5.2.0
MSG_NOERROR integer  
MSG_EXCEPT integer