Linux进程间通讯之信号量sem

时间：2010-12-25 来源：willwwei

信号量sem: willisway1: #include <stdio.h>
#include <string.h>
#include <stdlib.h> #include <sys/stat.h>
#include <fcntl.h> #include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h> #define NR 100
#define SIZE 1024 static int semid; int sem_init(void)
{
    int arg;     semid = semget(IPC_PRIVATE, 1, IPC_CREAT | 0600);     arg = 1;
    semctl(semid, 0, SETVAL, arg);     return 0;
}
int sem_destroy(void)
{
    return semctl(semid, 0, IPC_RMID);
} int sem_lock(void)
{
    struct sembuf dec = {
                      .sem_num = 0,
                      .sem_op = -1,
                      .sem_flg = SEM_UNDO
                        };
    semop(semid, &dec, 1);
} int sem_unlock(void)
{
    struct sembuf inc = {
                      .sem_num = 0,
                      .sem_op = 1,
                      .sem_flg = SEM_UNDO
                        };
    semop(semid, &inc, 1); } int main(void)
{
    pid_t pid;
    int i, ret;
    int fd, num;
    char buf[SIZE];     sem_init();     fd = open("./test", O_RDWR | O_CREAT, 0600);     for (i = 0; i < NR; ++i)
    {
        pid = fork();
        if (pid == 0)
        {             ret = sem_lock();             lseek(fd, 0, SEEK_SET);
            ret = read(fd, buf, SIZE);
            usleep(1);
            buf[ret] = '\0';
            num = atoi(buf);
            num += 1;             snprintf(buf, SIZE, "%d", num);
            lseek(fd, 0, SEEK_SET);
            usleep(1);
            ret = write(fd, buf, strlen(buf));
            fsync(fd);
            usleep(1);
            ret = sem_unlock();             exit(0);
        }
    }     for (i = 0; i < NR; ++i)
    {
        wait(NULL);
    }     close(fd);     sem_destroy();     return 0;
} 分析：用于多个进程对于共享内存的存取。