Qt生产者消费者实验(2)：等待条件QWaitCondition

/*
使用QWaitCondition和QMutex可以实现比信号量更精确的控制
*/

#include <QtCore>
#include <iostream>

//const int DataSize = 100000;
//const int BufferSize = 4096;


const int DataSize = 100;
const int BufferSize = 100;
char buffer[BufferSize];

//与信号量不同的程序
QWaitCondition bufferIsNotFull; //QWaitCondition允许在一定条件下触发其它多个线程
QWaitCondition bufferIsNotEmpty;
QMutex mutex;
int usedSpace = 0;//不是信号量，而是用来代表在缓冲器中存在多少个“用过的”字节

//生产者
class Producer : public QThread
{
public:
    void run();
};

void Producer::run()
{
    for (int i = 0; i < DataSize; ++i) {
        mutex.lock();//锁定：保护对usedSpace变量的访问
        //如果缓冲区都是用过的字节，那么就等待
        while (usedSpace == BufferSize)
            bufferIsNotFull.wait(&mutex);//wait的过程：解锁－>阻塞当前线程－>满足条件－>锁定－>返回
        buffer[i % BufferSize] = "ACGT"[uint(rand()) % 4];
        std::cerr<<"P";//代表一次生产者线程的运行
        ++usedSpace;
        bufferIsNotEmpty.wakeAll();//Wakes all threads waiting on the wait condition.
        mutex.unlock();//解锁
    }
}

//消费者
class Consumer : public QThread
{
public:
    void run();
};

void Consumer::run()
{
    for (int i = 0; i < DataSize; ++i) {
        mutex.lock();//
        //如果缓冲区里“用过的”字节数目为0，则等待
        while (usedSpace == 0)
            bufferIsNotEmpty.wait(&mutex);
        //std::cerr << buffer[i % BufferSize];
        char Cons = buffer[i % BufferSize];
        std::cerr<<"c";
        --usedSpace;
        bufferIsNotFull.wakeAll();
        mutex.unlock();
    }
    std::cerr << std::endl;
}

int main()
{
    Producer producer;
    Consumer consumer;
    producer.start();
    consumer.start();
    producer.wait();
    consumer.wait();
    return 0;
}

执行结果

(1)

const int DataSize = 100;
const int BufferSize = 1;

PcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPc

(2)

const int DataSize = 100;
const int BufferSize = 10;

结果1

PPPPPPPPPPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcccccccccc

结果2

PPPPPPPPPPcPcPcPcPcPcPcPcPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPcc

结果3

PPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPcccccccccc

(3)

const int DataSize = 100;
const int BufferSize = 100;

PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPcccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc