linux多进程通信

信号量机制实现进程通信：

使用sem_open，sem_unlink，sem_getvalue，sem_post，sem_wait，sem_close，等信号量机制

1.sem_sync.h

#ifndef _SEM_SYNC_H_
#define _SEM_SYNC_H_
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#include <semaphore.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

char SEM_A_TASK_IS_FREE[]= "a_task_is_free";
char SEM_B_TASK_IS_FREE[]= "b_task_is_free";

#endif

2.进程a

#include "sem_sync.h"

int main()
{
sem_t *sem_a_task_is_free;
sem_t *sem_b_task_is_free;
int val;

sem_a_task_is_free = sem_open(SEM_A_TASK_IS_FREE, O_CREAT, 0644, 1);
sem_b_task_is_free = sem_open(SEM_B_TASK_IS_FREE, O_CREAT, 0644, 0);
if (sem_a_task_is_free == SEM_FAILED || sem_b_task_is_free == SEM_FAILED)
{
perror("unable to create semaphore");
sem_unlink(SEM_A_TASK_IS_FREE);
exit(-1);
}
//while (1 == 1)
{
printf("run a task......\n");
getchar();

sem_getvalue(sem_a_task_is_free, &val);
printf("The sem is %d\n", val);
sem_post(sem_a_task_is_free);
sem_getvalue(sem_a_task_is_free, &val);
printf("The sem after sem post is %d\n", val);
printf("send->a_task_is_free\n");

printf("\nwaite sem_b_task_is_free\n");
//sem_wait(sem_b_task_is_free);
printf("recv<-sem_b_task_is_free\n");
}

sem_close(sem_a_task_is_free);
sem_unlink(SEM_A_TASK_IS_FREE);

_exit(0);
}

//gcc a.c -lpthread  -o a

3.进程b

#include "sem_sync.h"

int main()
{
int val;
sem_t *sem_a_task_is_free;
sem_t *sem_b_task_is_free;

sem_a_task_is_free = sem_open(SEM_A_TASK_IS_FREE, O_CREAT, 0644, 0);
sem_b_task_is_free = sem_open(SEM_B_TASK_IS_FREE, O_CREAT, 0644, 1);
if (sem_a_task_is_free == SEM_FAILED || sem_b_task_is_free == SEM_FAILED)
{
perror("unable to create semaphore");
sem_unlink(SEM_B_TASK_IS_FREE);
exit(-1);
}

//while (1 == 1)
{
printf("\nrun b_task......\n");
sem_getvalue(sem_a_task_is_free, &val);
printf("The sem is %d\n", val);
sleep(1);
//sem_post(sem_b_task_is_free);
printf("send->sem_b_task_is_free\n");
printf("\nwaite a_task_is_free\n");
sem_getvalue(sem_a_task_is_free, &val);
printf("The sem 2 is %d\n", val);
sem_wait(sem_a_task_is_free);
sem_getvalue(sem_a_task_is_free, &val);
printf("The sem 3 is %d\n", val);
printf("recv<-a_task_is_free\n");
}

sem_close(sem_a_task_is_free);
sem_close(sem_b_task_is_free);

sem_unlink(SEM_B_TASK_IS_FREE);
exit(0);
}

//gcc b.c -lpthread -o b

#./a

#./b

备注：只要信号量没有释放，sem_unlink，那信号量值将保持不变，sem_post将使信号量增加1，sem_wait将使信号量减1.

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