Usage sample of unix semaphore

There are two types of semaphore on unix system:

-- System V信号量(命名信号量)

#include <sys/sem.h>

int semctl(int sem_id, int sem_num, int command, ...);

int semget(key_t key, int num_sems, int sem_flags);

int semop(int sem_id, struct sembuf *sem_ops, size_t num_sem_ops);

-- POSIX无名信号量

int sem_init(sem_t *sem, int pshared, unsigned int value);

int sem_wait(sem_t * sem);

int sem_trywait(sem_t * sem);

int sem_post(sem_t * sem);

int sem_getvalue(sem_t * sem, int * sval);

int sem_destroy(sem_t * sem);

无名信号量不能用在进程间通信, 命名信号量可以用在进程间通信。

-- Sample program of POXIS semaphore --

#include <pthread.h>

#include <semaphore.h>

#include <stdio.h>

#include <unistd.h>

int data;

sem_t sem;

void *HandleDataWrite(void *args)

{

while(true)

{

sleep(2);

sem_post(&sem);

data=100;

}

return NULL;

}

void *HandleDataRead(void *args)

{

while(true)

{

sleep(3);

sem_wait(&sem);

printf("Data=%d/n",data);

}

return NULL;

}

int main(void){

pthread_t tread,twrite;

sem_init(&sem,true,0);

pthread_create(&tread,NULL,HandleDataRead,NULL);

pthread_create(&twrite,NULL,HandleDataWrite,NULL);

pthread_join(tread,NULL);

pthread_join(twrite,NULL);

}