在 C 中使用信号量

Question

我正在学习如何在 C (linux) 中使用信号量。

我想问你：

如何判断订单是立即执行，还是等待？

Example我去睡觉理发师：

在函数中：

    void *customer(void *number) {
    int num = *(int *)number;

    // Leave for the shop and take some random amount of
    // time to arrive.
    printf("Customer %d leaving for barber shop.\n", num);
    randwait(5);
    printf("Customer %d arrived at barber shop.\n", num);

    // Wait for space to open up in the waiting room...
    sem_wait(&waitingRoom);
    printf("Customer %d entering waiting room.\n", num);

    // Wait for the barber chair to become free.
    sem_wait(&barberChair);

    // The chair is free so give up your spot in the
    // waiting room.
    sem_post(&waitingRoom);

    // Wake up the barber...
    printf("Customer %d waking the barber.\n", num);
    sem_post(&barberPillow);

    // Wait for the barber to finish cutting your hair.
    sem_wait(&seatBelt);

    // Give up the chair.
    sem_post(&barberChair);
    printf("Customer %d leaving barber shop.\n", num);
}

在线sem_wait(&waitingRoom);是否可以检查等待-真假？

我的意思是：

int time = sem_wait(&waitingRoom);
if(time != 0)
 printf("YOU MUST WAIT!");

或

   int i = isSemaphoreFree()...

我希望你能理解我，对不起我的英语:-)

Answer 1

看看sem_trywait()sem_... docs

如果信号量当前被阻塞，这将立即返回错误。