Qt线程初步

默默地EEer，原文地址：

http://www.cnblogs.com/hebaichuanyeah/p/5618781.html

在调用linux环境下线程API写Cpp时，发现异常蛋疼，要么线程函数不能是类的成员函数，要么必须是类的static成员函数（意味着调用的成员变量也必须是static……其实还是不属于类）。

Qt提供一套线程机制，只要继承QThread基类并重新实现void run()函数即可。

新建thread.h继承Qthread，并在thread.cpp中实现它。

thread.h

#include "QThread"

class Thread : public QThread
{
    Q_OBJECT
public:
    Thread();
 //   void setMessage(const Qstring &message);
    void setRun();
    void stop();
    bool getState();
protected:
    void run();
private:
   // QString messageStr;
    volatile bool enable; 
signals:
    void OutMessage(QString message);
};

 thread.cpp，在run函数中循环1秒触发一个信号输出信息。

#include "thread.h"

Thread::Thread()
{
    enable = true;
}

void Thread::run()
{
    while(true)
    {
        if(enable)
        {
            this->OutMessage(tr("I'm run : thread 1"));
            msleep(1000);
        }
    }
}
void Thread::stop()
{
    enable = false;
}
void Thread::setRun()
{
    enable = true;
}
bool  Thread::getState()
{
    return enable;
}

 mainwindow.h，定义一些Qt控件

#ifndef MAINWINDOW_H
#define MAINWINDOW_H


#include <QMainWindow>
#include <QLabel>
#include <QGridLayout>
#include <QPushButton>
#include <QTextEdit>
#include <QDoubleValidator>
#include <QComboBox>
#include <QTranslator>

#include "thread.h"

#define PI  3.14592653589

class MainWindow  : public QMainWindow
{
    Q_OBJECT
public:
    MainWindow();
    ~MainWindow();
private:
    QWidget* mainWindow;
    QGridLayout * mainLayout;
    QTextEdit * messageEdit;
    QPushButton * clearButton;
    QPushButton * runStopButton;
    Thread * backThread;
private slots:
    void updateMessage(QString message);
    void clearMessage();
    void runStopThread();

};

#endif

 mainwindow.cpp

#include "mainwindow.h"
#include <QPainter>


MainWindow :: MainWindow()
{
    mainWindow = new QWidget;
    this->setCentralWidget(mainWindow);

    backThread = new Thread();
    backThread->start();


    clearButton = new QPushButton(tr("clear"));
    clearButton->setSizePolicy(QSizePolicy::Fixed,QSizePolicy::Fixed);
    runStopButton = new QPushButton(tr("stop"));
    messageEdit = new QTextEdit();
    messageEdit->setReadOnly(true);
    mainLayout = new QGridLayout;

    mainLayout->addWidget(messageEdit,0,0,5,5);
    mainLayout->addWidget(clearButton,1,5,1,1);
    mainLayout->addWidget(runStopButton,0,5,1,1);

    mainWindow->setLayout(mainLayout);

    QObject::connect(clearButton,SIGNAL(clicked()),this,SLOT(clearMessage()));
    QObject::connect(runStopButton,SIGNAL(clicked()),this,SLOT(runStopThread()));

    QObject::connect(backThread,SIGNAL(OutMessage(QString)),this,SLOT(updateMessage(QString)));

    this->setWindowTitle(tr("thread test~"));
    this->resize(QSize(300,100));
 //   this->setFixedSize(200,100);
}

MainWindow :: ~MainWindow()
{
    mainWindow->deleteLater();
    mainLayout->deleteLater();
    messageEdit->deleteLater();
    clearButton->deleteLater();
    runStopButton->deleteLater();
}

void MainWindow::updateMessage(QString message)
{
    messageEdit->append(message);
}
void MainWindow::clearMessage()
{
    messageEdit->clear();
}
void MainWindow::runStopThread()
{
    if(backThread->getState())
    {
        backThread->stop();
        runStopButton->setText(tr("run"));
    }
    else
    {
        backThread->setRun();
        runStopButton->setText(tr("stop"));

    }     
}

 运行：

后台线程不断打印信息，通过run/stop按钮停止/启动。

同时，Qt提供一套线程同步机制

QMutex（互斥锁），QReadWriteLock（读写锁），QSemaphore（信号量），QWaitCondition（阻塞等待一个条件）。

使用都很简单，其中QWaitCondition，调用bool wait(QMutex *mutex, unsigned long time = ULONG_MAX)成员函数阻塞。 void wakeOne()和void wakeAll()唤醒一处和所有阻塞。（类似于C#里面的ManualResetEvent 类，.WaitOne()   .Set()）