PHP手册中shm常用函数及部分解释——Semaphore模块

一、Semaphore模块：
     包括三个部分：Semaphore（互斥锁），shm（共享内存），inter-process messaging (IPC)。


二、SHM

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

SHMMAX：　共享内存的最大值，一般是131072字节(128K)
SHMMIN：　最小内存，一般是１字节
SHMMNI：　共享内存的最大段数，一般是100
SHMSEG：　每个进程最大段数，一般是6

三、配置
sysvshm.init_mem       A default size of the shared memory segment.

四、函数列表：

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_queue_exists — Check whether a message queue exists
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_has_var — Check whether a specific entry exists
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