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.
表格 1. Limits of Shared Memory by the Unix
OS
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.
注: This extension is not available on Windows platforms.
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.
php.ini中的設定會影響這些函數的行為。
表格 2. Semaphore Configuration Options