OS

OS 中的 P-V 操作
生产者-消费者 && 哲学家 && 读者-写者 && 理发师-顾客

生产者-消费者

semaphore mutex = 1;
semaphore empty = n;
semaphore full = 0;

Producer(){
    while(1){
        produce;
        P(empty);

        P(mutex);
        add to buffer;
        V(mutex);

        V(full);
    }
}

Consumer(){
    while(1){
        P(full);

        P(mutex);
        remove from buffer;
        V(mutex);

        V(empty);
        consume;
    }
}

哲学家就餐

semaphore chop[5] = {1, 1, 1, 1, 1};
semaphore mutex = 1;

Pi(){
    while(1){
        think;

        P(mutex);
            P(chop[i]);
            P(chop[(i+1)%5]);
        V(mutex);

        eat;

        V(chop[i]);
        V(chop[(i+1)%5]);
    }
}

读者-写者

int count = 0;
semaphore mutex = 1;
semaphore rw = 1;
semaphore w = 1;

Writer(){
    while(1){
        // P(w);    // 写优先信号
        P(rw);
        writing;
        V(rw);
        // V(w);
    }
}

Reader(){
    while(1){
        // P(w);    // 写优先信号
        P(mutex);
        if(count == 0)
            P(rw);
        count++;
        V(mutex);
        // V(w);

        reading;

        P(mutex);
        count--;
        if(count == 0)
            V(rw);
        V(mutex);
    }
}

理发师-顾客

int waiting = 0;
int chairs = N;
semaphore customers = 0;
semaphore barbers = 0;
semaphore mutex = 1;

Barbers(){
    while(1){
        P(customers);
        P(mutex);
        waiting--;
        V(barbers);
        V(mutex);
        cut hair;
    }
}

Customes(){
    P(mutex);
    if(waiting < chairs){
        waiting++;
        V(customes);
        V(mutex);
        P(barbers);
        get haircut;
    }
    else
        V(mutex);
}