sem_func.c

这是自己写的一个关于经典ipc问题－读者写者的实现。（用信号量实现）

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/stat.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <stdio.h>
#include "sem_func.h"

int init(int *id, unsigned int value, char *sem_ident)
{
    int oflag, sem_id, i;
    union semun arg;
    struct semid_ds seminfo;

    oflag = SVSEM_MODE | IPC_CREAT | IPC_EXCL;


    if ( (sem_id = semget(ftok(sem_ident, 0), 1, oflag)) >= 0) {
        *id = sem_id;

        arg.val = value;
        semctl(*id, 0, SETVAL, arg);
    } else if (errno == EEXIST) {
        sem_id = semget(ftok(sem_ident, 0), 1, SVSEM_MODE);
        arg.buf = &seminfo;
        for (i = 0; i < 10; i++) {
            semctl(sem_id, 0, IPC_STAT, arg);
            if (arg.buf->sem_otime != 0) {
                return 0;
            }
            sleep(1);
        }
        printf("semget OK, but semaphore not initialized.\n");
        exit(1);
    } else {
        printf("semget error.\n");
        exit(1);
    }
    return 0;
}



int P(int *id)
{
    struct sembuf op;


    op.sem_num = 0;
    op.sem_op = 1;
    op.sem_flg = 0;
    if (semop(*id, &op, 1) < 0)
        return (-1);
    return (0);
}




int V(int *id)
{
    struct sembuf op;

    op.sem_num = 0;
    op.sem_op = -1;
    op.sem_flg = 0;
    if (semop(*id, &op, 1) < 0)
        return (-1);
    return 0;
}