【操作系统】经典的同步问题(生产者消费者问题, 哲学家进餐问题, 读写问题)

//生产者消费者问题
//记录型信号量
//缓冲池中有n个缓冲区, 互斥信号量mutex, 
//信号量empty表示空缓冲区数量, full表示满缓冲区的数量
int in = out = 0;
item buffer[n];
semaphore mutex = 1, empty = n, full = 0;
void producer() {
    do {
        producer an item nextp;
        wait(empty);
        wait(mutex);
        buffer[in] = nextp;
        in = (in + 1) % n;
        signal(mutex);
        signal(full);
    } while(true);
}
void consumer() {
    do {
        wait(full);
        wait(mutex);
        nextc = buffer[out];
        out = (out + 1) % n;
        signal(mutex);
        signal(empty);
        consumer the item in nextc;
    } while(true);
}
void main() {
    cobegin
        producer();
        consumer();
    coend
}

//AND型信号量
//Swait(empty, mutex)代替wait(empty)和wait(mutex)
//Ssignal(mutex,full)代替signal(mutext)和signal(full)
//Swait(full, mutex)代替wait(full)和wait(mutex)
//Ssignal(mutex, empty)代替signal(mutex)和signal(empty)
int in = out = 0;
item buffer[n];
semaphore mutex = 1, empty = n, full = 0;
void producer() {
    do {
        producer an item nextp;
        Swait(empty, mutex);
        buffer[in] = nextp;
        in = (in + 1) % n;
        Ssignal(mutex, full);
    } while(true);
}
void consumer() {
    do {
        Swait(full, mutex);
        nextc = buffer[out];
        out = (out + 1) % n;
        Ssignal(mutex, empty);
        consumer the item in nextc;
    } while(true);
}
void main() {
    cobegin
        producer();
        consumer();
    coend
}

//管程
//建立管程producerconsumer,PC
/*
put(x), 生产者利用该过程将自己生产的产品投放到缓冲池中, 并用整型变量count表示缓冲池中已有的产品数目,当
count>=N时, 表示缓冲池已满,生产者需等待.
get(x), 消费者利用该过程从缓冲池中取出一个产品, 当count<=0时, 表示缓冲池已无可用的产品, 消费者需等待
condition 为notfull和notempty
cwait(condition), 当管程被一个进程占用时, 其他进程调用该进程时阻塞, 并挂在条件condition的队列上
csignal(condition), 唤醒在cwait执行后阻塞在条件condition队列上的进程, 如果这样的进程不止一个, 则选择其中一个
实施唤醒操作, 如果队列为空, 则无操作而返回.
*/
Monitor producerconsumer {
    item buffer[N];
    int in, out;
    condition notfull, notempty;
    int count;
    public:
        void put(item x) {
            if (count >= N) cwait(notfull);
            buffer[in] = x;
            in = (in + 1) % N;
            count++;
            ssignal(notempty);
        }
        void get(item x) {
            if (count <= 0) cwait(notempty);
            x = buffer[out];
            out = (out + 1) % N;
            count--;
            csignal(notfull);
        }
        {
            in = 0;
            out = 0;
            count = 0;
        }
}PC;

void producer() {
    item x;
    while (true) {
        producer an item in nextp;
        PC.put(x);
    }
}
void consumer() {
    item x;
    while (true) {
        PC.get(x);
        consumer the item in nextc;
    }
}
void main() {
    cobegin
        producer();
        consumer();
    coend
}

do {
    wait(chopstick[i]);
    wait(chopstick[(i + 1) % 5]);
    //eat
    signal(chopstick[i]);
    signal(chopstick[(i + 1) % 5]);
    //think
} while (true);

//AND型信号量
semaphore chopstick[5] = {1, 1, 1, 1, 1};
do {
    //think
    Swait(chopsitck[(i + 1) % 5], chopsitck[i]);
    //eat
    Ssignal(chopsitck[(i + 1) % 5], chopsitck[i]);
} while (true);

//记录型信号量
semaphore rmutext = 1, wmutext = 1;
int readcount = 0;
void Reader() {
    do {
        wait(rmutex);
        if (readcount == 0) {
            wait(wmutex);
        }
        readcount++;
        signal(rmutex);
        
        perform read operation;
        
        wait(rmutex);
        readcount--;
        if (readcount == 0) {
            signal(wmutext);
        }
        signal(rmutex);
    } while (true);
}

void Writer() {
    do {
        wait(wmutex);
        perform write operation;
        signal(wmutex);
    } while (true);
}
void main() {
    cobegin
        Reader();
        Writer();
    coend
}

//信号量集
int RN;
semaphore L = RN, mx = 1;
void Reader() {
    do {
        Swait(L, 1, 1);
        Swait(mx, 1, 0);
        
        perform read operation;
        
        Ssignal(L, 1);
    } while (true);
}
void Writer() {
    do {
        Swait(mx, 1, 1; L, RN, 0);
        perform write operation;
        Ssignal(mx, 1);
    } while (true);
}

void main() {
    cobegin
        Reader();
        Writer();
    coend
}