Qt生产者消费者实验：等待条件QWaitCondition

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/*
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)

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const int DataSize = 100;

const int BufferSize = 1;

PcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPc

(2)

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const int DataSize = 100;

const int BufferSize = 10;

结果1

PPPPPPPPPPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcPcccccccccc

结果2

PPPPPPPPPPcPcPcPcPcPcPcPcPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPcc

结果3

PPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPccccccccccPPPPPPPPPPcccccccccc

(3)

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const int DataSize = 100;

const int BufferSize = 100;

PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP