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Qt实现多线程编程的两种方式


Qt实现多线程编程的两种方式

方式一: 继承自QThread类,覆写run函数。此实现方法只有run函数内的代码是运行在子线程内。

代码示例:

#ifndef QDEMOTHREAD_H
#define QDEMOTHREAD_H

#include <QThread>
#include <QDebug>

class QDemoThread : public QThread
{
Q_OBJECT

public:
QDemoThread(QObject* parent = nullptr);
~QDemoThread();

protected:
void run() override;

public:
void stop();

private:
bool flag;
};

#endif // QDEMOTHREAD_H

#include "qdemothread.h"

QDemoThread::QDemoThread(QObject* parent) : QThread(parent)
{

}

QDemoThread::~QDemoThread()
{

}

void QDemoThread::run()
{
flag = true;
while(flag)
{
qDebug() << "thread id:" << QThread::currentThreadId();
sleep(1);
}
}

void QDemoThread::stop()
{
flag = false;
if(isRunning())
{
exit(); // 结束线程
wait(); // 等待退出
}
}

#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent) :
QWidget(parent),
ui(new Ui::Widget)
{
ui->setupUi(this);

demoThread = new QDemoThread(this);

qDebug() << "main thread id:" << QThread::currentThreadId();
}

Widget::~Widget()
{
demoThread->stop(); // 退出线程
delete ui;
}

void Widget::on_pushButton_clicked()
{
if(!demoThread->isRunning())
{
demoThread->start(); // 启动线程
}
}

运行效果:

Qt实现多线程编程的两种方式_Qt

方式二: 创建一个QThread和QWorker(继承自QObject)类对象,使用moveToThread函数移动到thread中运行,通过thread类start信号和worker的init槽函数绑定,init槽函数内是一些初始化操作,然后定义个定时器,周期触发doWork()。

网上有很多教程是在doWork()中使用while(isRunning)死循环的形式,不建议这么干,如果线程一直在doWork中死循环,那么他是无法接收到来自外部的信号的。推荐的方法是用定时器周期触发。

示例代码:

QWorker类:

#ifndef QWORKER_H
#define QWORKER_H

#include <QObject>
#include <QThread>
#include <QDebug>

class QWorker : public QObject
{
Q_OBJECT
public:
explicit QWorker(QObject *parent = nullptr);
~QWorker();

signals:
void newData(QByteArray data); // 将本类内的私有数据通过该信号发射出去,供外部使用

public slots:
void init(); // 一些必要的初始化操作写在此函数内
void doWork(); // 一些耗时操作写在此函数内
void writeData(const char* buf, qint64 len); // 供外部使用的操作接口
};

#endif // QWORKER_H

#include "qworker.h"

QWorker::QWorker(QObject *parent) : QObject(parent)
{
qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId();
}

QWorker::~QWorker()
{
qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId();
}

void QWorker::init()
{
qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId();
}

void QWorker::doWork()
{
static int count = 0;
qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId() << ">>>" << count++;
}

void QWorker::writeData(const char* buf, qint64 len)
{
qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId() << ">>>" << QByteArray(buf, len);
}

主线程:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "qworker.h"
#include <QTimer>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
Q_OBJECT

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

private slots:
void on_pushButton_clicked();

private:
Ui::MainWindow *ui;
QWorker* worker;
QThread* thread;
QTimer* timer;

signals:
void writeData(const char* buf, qint64 len);
void stopWork();
};

#endif // MAINWINDOW_H

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);

qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId();

timer = new QTimer(this);

thread = new QThread(); // 不要指定parent
worker = new QWorker(); // 不要指定parent

// thread的finished和deleteLater相连接后,在thread退出时自动删除thread对象,无需手动delete thread
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
// thread的finished和worker的deleteLater相连接后,在thread退出时自动删除worker对象,无需手动delete worker
connect(thread, SIGNAL(finished()), worker, SLOT(deleteLater()));
connect(thread, SIGNAL(started()), worker, SLOT(init()));

connect(timer, SIGNAL(timeout()), worker, SLOT(doWork()));

connect(this, SIGNAL(writeData(const char*,qint64)), worker, SLOT(writeData(const char*,qint64)));

worker->moveToThread(thread);

thread->start();

timer->start(1000); // 1000ms执行一次doWork()
}

MainWindow::~MainWindow()
{
if(timer->isActive())
{
timer->stop();
}

if(thread->isRunning())
{
thread->quit();
thread->wait();
}

qDebug() << __FUNCTION__ << "Thread ID:" << QThread::currentThreadId();

delete ui;
}

void MainWindow::on_pushButton_clicked()
{
emit writeData("hello world\r\n", 13);
}

程序界面:

Qt实现多线程编程的两种方式_#include_02

运行后控制台打印信息如下:

Qt实现多线程编程的两种方式_Qt_03


可以看到的是,MainWindow和QWorker的构造函数中都显示线程ID为0x336c,而在QWorker的析构函数中显示线程ID为0x22a8,这说明moveToThread确实将worker移动到了thread中;而且还可以看到的是,QWorker的槽函数init、doWork、writeData也都是运行在了子线程中!

ends…


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