interprocess Communication-Semaphore

Semaphore: It describes the current quantity of a resource. It is intended for inter-process synchronization, which is equivalent to a counter, which itself does not have the function of data exchange, but rather by controlling other communication resources to achieve interprocess communication.

When a process to access critical resources, the first to carry out the P operation request resources, when greater than 0 o'clock, the resource can request, after the application, if 0, the process is suspended, when the process no longer accesses the semaphore control of the resource, the V operation, if there is a process hangs, wake the waiting process to resume access, if there is no suspended process Just add 1 to it.

Inter-Process synchronization: Access to critical resources is sequential, one execution is complete, and the other can be executed.

Note: The operation of the Semaphore is atomic operation, because the main function of the semaphore is to maintain the mutual exclusion of resources or multi-process synchronization access, and in the initialization and creation of the semaphore can not guarantee its atomic operation.

To create the semaphore: semget (key_t key,int nsems,int semflg);

P,v Operation:

SEMOP (int semid,struct sembuf* buf,unsigned nsops);//p/v operation on the number of semaphores on the current semaphore set

Release semaphore: semctl (int semid, int semnue,int cmd)//CMD instruction operation on the number of semaphores on the current semaphore set.

Union Semun {

int Val; The value used

struct Semid_ds *buf; Ipc_stat, Ipc_set use buffer

unsigned short *array; GETALL, SETALL used array

struct Seminfo *__buf; Ipc_info (Linux-specific) using buffers

};

Comm.h

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Comm.c

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TEST.c
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Operation Result:

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interprocess Communication-Semaphore