Semaphore, Shared Memory and IPC Functions

简介

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.

Note: 本扩展模块在 Windows 平台下不可用。

需求

要编译本扩展模块无需外部库文件。

安装

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.

运行时配置

这些函数的行为受 php.ini 的影响。

Semaphore Configuration Options
Name Default Changeable Changelog
sysvmsg.value "42" PHP_INI_ALL  
sysvmsg.string "foobar" PHP_INI_ALL  
有关 PHP_INI_* 常量进一步的细节与定义参见php.ini 配置选项

资源类型

预定义常量

以下常量由本扩展模块定义,因此只有在本扩展模块被编译到 PHP 中,或者在运行时被动态加载后才有效。

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

Table of Contents



Host by Alair