一个Qt线程的例子，用于说明QWaitCondition的作用

 

 

描述可能比较麻烦，还是直接上代码吧！

main.cpp

 

#include <QApplication>
#include "mainpage.h"

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

    MainPage page;
    page.show();

    return a.exec();
}

mainpage.h

 

 

#ifndef MAINPAGE_H
#define MAINPAGE_H

#include <QWidget>

#include "thread1.h"


class MainPage : public QWidget
{
    Q_OBJECT

public:
    explicit MainPage(QWidget *parent = 0);
    ~MainPage();

    thread1 *th1;

private slots:
    void doClick();

};

#endif // MAINPAGE_H

thread1.h

 

 

#ifndef THREAD1_H
#define THREAD1_H

#include <QThread>
#include <QWaitCondition>
#include "thread2.h"
#include <QMutex>

class thread1 : public QThread
{
    Q_OBJECT
public:
    explicit thread1(QObject *parent = 0);

    void run();
    void wakeFunc();

private:
    QWaitCondition cond;
    QMutex mutex;
    thread2 th2;
};

#endif // THREAD1_H

thread2.h

 

 

#ifndef THREAD2_H
#define THREAD2_H

#include <QThread>

class thread2 : public QThread
{
    Q_OBJECT
public:
    explicit thread2(QObject *parent = 0);

    void run();
};

#endif // THREAD2_H

mainpage.cpp

 

 

#include "mainpage.h"
#include <QDebug>
#include <QPushButton>

MainPage::MainPage(QWidget *parent) :
    QWidget(parent)
{
    th1=new thread1;

    this->resize(100, 40);

    QPushButton *pb=new QPushButton("按钮", this);
    pb->resize(50, 20);
    pb->move(10, 10);
    connect(pb, SIGNAL(clicked()), this, SLOT(doClick()));
}

MainPage::~MainPage()
{
}

void MainPage::doClick()
{
    qDebug()<<"button clicked!";
    th1->wakeFunc();
}

thread1.cpp

 

 

#include "thread1.h"
#include <QDebug>

thread1::thread1(QObject *parent) :
    QThread(parent)
{
}

void thread1::wakeFunc()
{
    if(!isRunning()){
        start();
    }else{
        cond.wakeOne();
    }
}

void thread1::run()
{
    static int x=0;
    qDebug()<<"进入thread1的run函数";
    while(true){
        qDebug()<<"-------> 1 <---------";
        mutex.lock();
        if(++x>3) th2.start();
        qDebug() << "进入thread1的while循环,x值为"<<x;
        cond.wait(&mutex);   //当处于wait状态时mutex会被暂时释放，并阻塞在这个地方；当线程被cond.wakeOne()等唤醒时，mutex又会被重新锁定，并继续运行
        mutex.unlock();
        qDebug()<<"-------> 2 <---------";
    }
}

thread2.cpp

 

 

#include "thread2.h"
#include <QDebug>

thread2::thread2(QObject *parent) :
    QThread(parent)
{
}

void thread2::run()
{
    qDebug()<<"线程2已激活";
}

运行效果：

 

（1）按钮点击一次时的调试输出

 

（3）按钮点击多次时的调试输出

 

结论：借助网友的说法，在debug里面可以看到线程1的run函数只进入了一次，虽然我们调用了它很多次。也就是说使用waitCondition可以让线程进入休眠而不用退出。