Qt waitCondition使用例子

下面是一个使用 QWaitCondition 的例子，其中有一个线程不断向一个共享的缓冲区中写入数据，另一个线程从缓冲区中读取数据，如果缓冲区为空，则等待直到有数据可读。

#include <QCoreApplication>
#include <QDebug>
#include <QThread>
#include <QMutex>
#include <QWaitCondition>

const int BUFFER_SIZE = 10;

class Buffer
{
public:
    Buffer()
        : m_readIndex(0)
        , m_writeIndex(0)
        , m_dataCount(0)
    {
    }

    void write(int data)
    {
        QMutexLocker locker(&m_mutex);
        while (m_dataCount == BUFFER_SIZE) {
            m_notFull.wait(&m_mutex);
        }
        m_data[m_writeIndex] = data;
        m_writeIndex = (m_writeIndex + 1) % BUFFER_SIZE;
        m_dataCount++;
        m_notEmpty.wakeAll();
    }

    int read()
    {
        QMutexLocker locker(&m_mutex);
        while (m_dataCount == 0) {
            m_notEmpty.wait(&m_mutex);
        }
        int data = m_data[m_readIndex];
        m_readIndex = (m_readIndex + 1) % BUFFER_SIZE;
        m_dataCount--;
        m_notFull.wakeAll();
        return data;
    }

private:
    int m_readIndex;
    int m_writeIndex;
    int m_dataCount;
    int m_data[BUFFER_SIZE];
    QMutex m_mutex;
    QWaitCondition m_notEmpty;
    QWaitCondition m_notFull;
};

class WriterThread : public QThread
{
public:
    WriterThread(Buffer* buffer)
        : m_buffer(buffer)
    {
    }

protected:
    void run() override
    {
        for (int i = 0; i < 100; i++) {
            m_buffer->write(i);
            msleep(100);
        }
    }

private:
    Buffer* m_buffer;
};

class ReaderThread : public QThread
{
public:
    ReaderThread(Buffer* buffer)
        : m_buffer(buffer)
    {
    }

protected:
    void run() override
    {
        for (int i = 0; i < 100; i++) {
            int data = m_buffer->read();
            qDebug() << data;
            msleep(50);
        }
    }

private:
    Buffer* m_buffer;
};

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    Buffer buffer;
    WriterThread writerThread(&buffer);
    ReaderThread readerThread(&buffer);
    writerThread.start();
    readerThread.start();

    return a.exec();
}

在上述代码中，Buffer 类是一个共享的缓冲区，其中包含一个数组和三个同步对象：QMutex、QWaitCondition m_notEmpty 和 QWaitCondition m_notFull。WriterThread 类是一个写入线程，不断向缓冲区中写入数据。ReaderThread 类是一个读取线程，从缓冲区中读取数据。在写入线程中，如果缓冲区已满，则调用 m_notFull.wait(&m_mutex) 等待，直到缓冲区不满为止。在读取线程中，如果缓冲区为空，则调用 m_notEmpty.wait(&m_mutex) 等待，直到缓冲区不空为止。在写入数据和读取数据后，分别调用 m_notEmpty.wakeAll() 和 m_notFull.wakeAll() 唤醒等待的线程。