Linux _sem 信号量 V_P

main1.c

#include <stdlib.h>
#include <stdio.h>

int main(void) 
{
    int i;

    for (i=0; i<5; i++) {

        /* ƒ£ƒ‚¡ŸΩÁ«¯----begin */
        printf("Process(%d) In\n", getpid());       
        sleep(1);
        printf("Process(%d) Out\n", getpid());
              /* ƒ£ƒ‚¡ŸΩÁ«¯----end */ 

        sleep(1);
    }

    return 0;
}

main2.c

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <stdlib.h>
#include <stdio.h>

#if defined(__GNU_LIBRARY__) && !defined(_SEM_SEMUN_UNDEFINED)                         
#else
    union semun {
        int val;                             
        struct semid_ds *buf;    
        unsigned short int *array; 
        struct seminfo *__buf;  
    };
#endif     

static sem_initial(int semid) 
{
    int ret;

    union semun semun;
    semun.val = 1;
    ret = semctl(semid, 0, SETVAL, semun);
    if (ret == -1) {
        fprintf(stderr, "semctl failed!\n");
    }

    return ret;
}

static int  sem_p(int semid)
{
    int ret;

    struct sembuf sembuf;
    sembuf.sem_op = -1;
    sembuf.sem_num = 0;
    sembuf.sem_flg = SEM_UNDO;
    ret = semop(semid, &sembuf, 1); 
    if (ret == -1) {
        fprintf(stderr, "sem_p failed!\n");
    }

    return ret;
}

static int  sem_v(int semid)
{
    int ret;

    struct sembuf sembuf;
    sembuf.sem_op = 1;
    sembuf.sem_num = 0;
    sembuf.sem_flg = SEM_UNDO;
    ret = semop(semid, &sembuf, 1); 
    if (ret == -1) {
        fprintf(stderr, "sem_v failed!\n");
    }

    return ret;
}

int main(int argc, char* argv[]) 
{
    int i;
    int ret;
    int semid;

    /* ªÒ»°–≈∫≈¡ø */
    semid = semget((key_t)1234, 1, 0666 | IPC_CREAT);
    if (semid == -1) {
        printf("semget failed!\n");
        exit(1);
    }

    /* ≥ı ºªØ–≈∫≈¡ø */
    if (argc > 1) {
        ret = sem_initial(semid);
        if (ret == -1) {
            exit(1);
        }
    }

    for (i=0; i<5; i++) {

        if (sem_p(semid) == -1) {
            exit(1);
        }

        /* ƒ£ƒ‚¡ŸΩÁ«¯----begin */
        printf("Process(%d) In\n", getpid());       
        sleep(1);
        printf("Process(%d) Out\n", getpid());
              /* ƒ£ƒ‚¡ŸΩÁ«¯----end */ 

        if (sem_v(semid) == -1) {
            exit(1);
        }

        sleep(1);
    }

    /* …æ≥˝–≈∫≈¡ø */

    return 0;
}