XCVII. Semaphore, Shared Memory and IPC Functions

Úvod

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.

Tabuľka 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.

Poznámka: Toto rozšírenie nie je dostupné na platformách Windows.

Požiadavky

Žiadne externé knižnice nie sú potrebné na vybudovanie tohto rozšírenia.

Inštalácia

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.

Runtime Konfigurácia

Správanie tejto funkcie je ovplyvnené nastaveniami v php.ini.

Tabuľka 2. Semaphore Configuration Options

NameDefaultChangeable
sysvmsg.value"42"PHP_INI_ALL
sysvmsg.string"foobar"PHP_INI_ALL
For further details and definition of the PHP_INI_* constants see ini_set().

Preddefinované Konštanty

Konštanty uvedené nižšie sú definované týmto rozšírením a budú dostupné iba keď rozšírenie bolo buď kompilované do PHP alebo dynamicky načítané za behu (runtime).

Tabuľka 3. System V message constants

ConstantType
MSG_IPC_NOWAITinteger
MSG_NOERRORinteger
MSG_EXCEPTinteger

Obsah
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