The QWaitCondition class provides a condition variable for synchronizing threads.
// 为同步线程提供条件变量

bool QWaitCondition::wait(QMutex *lockedMutex, unsigned long time = ULONG_MAX)
Releases the lockedMutex and waits on the wait condition.
// 开释 lockedMutex 并期待条件

void QWaitCondition::wakeAll()
Wakes all threads waiting on the wait condition.
激活所有期待 期待条件的 thread

include <QtCore>

include <iostream>

const int DataSize = 100000;
const int BufferSize = 4096;
char buffer[BufferSize];

QWaitCondition bufferIsNotFull;
QWaitCondition bufferIsNotEmpty;
QMutex mutex;
int usedSpace = 0;

class Producer : public QThread
{
public:

void run();

};

void Producer::run()
{

for (int i = 0; i < DataSize; ++i) {mutex.lock();
    while (usedSpace == BufferSize)// 曾经填满了缓冲区，是满的
        bufferIsNotFull.wait(&mutex); // 期待 bufferIsNotFull
    /*** 还有空间填充  **/
    buffer[i % BufferSize] = "ACGT"[uint(std::rand()) % 4];
    ++usedSpace;
    bufferIsNotEmpty.wakeAll();// 填充了之后，缓存区是非空的，会唤醒期待 bufferIsNotEmpty 的线程
    mutex.unlock();}

}

class Consumer : public QThread
{
public:

void run();

};

void Consumer::run()
{

for (int i = 0; i < DataSize; ++i)
{mutex.lock();
    while (usedSpace == 0)// 缓存区没有任何数据，就是空的
        bufferIsNotEmpty.wait(&mutex);// 期待 bufferIsNotEmpty
    /*** 缓存区有数据 **/
    std::cerr << buffer[i % BufferSize];
    --usedSpace;
    bufferIsNotFull.wakeAll();// 生产了数据后，缓存区是非满的，会唤醒期待 bufferIsNotFull 的线程
    mutex.unlock();}
std::cerr << std::endl;

}

int main()
{

Producer producer;
Consumer consumer;
producer.start();
consumer.start();
producer.wait();
consumer.wait();
return 0;

}