参考资料：实例来源 Qt编程快速入门
Qt帮助手册关于QMutex、QThread等
首先先看一个示例，(示例程序来自，Qt编程快速入门，我做了一些修改)。效果图如下，程序开启了三个绘图线程分别往QImage上绘制三角形、圆和矩形。
主程序中开启了一个定时器，会定时将图片清空。除此主程序的paintEvent事件中，将这个图片通过QPainter绘制显示出来。在绘图线程中，当对QImage操作时，就需要进行加锁，以保证同时只有一个线程可以对QImage进行操作。
绘图线程的代码。
1 #ifndef DRAWTHREADING_H
2 #define DRAWTHREADING_H
3 #include <QThread>
4 #include <QWidget>
5 #include <QMutex>
6 class DrawThread:public QThread
7 {
8 Q_OBJECT
9 public:
10 explicit DrawThread(QWidget *parent = 0);
11 void SetShape(int inputshape);
12 protected:
13 void run();
14 private:
15 int shape;
16 };
17
18 #endif // DRAWTHREADING_H
1 #include "drawthreading.h"
2
3 #include <QTime>
4 #include <QImage>
5 #include <QPainter>
6 #include "mainwindow.h"
7
8 DrawThread::DrawThread(QWidget *parent):QThread(parent)
9 {
10 shape = 0;
11 QTime tm;
12 tm = QTime::currentTime();
13 qsrand(tm.msec());
14 }
15 void DrawThread::SetShape(int inputshape)
16 {
17 shape = inputshape;
18 }
19 void DrawThread::run()
20 {
21 QImage* parentScene = ((MainWindow*)(this->parent()))->m_image;
22
23 while(true)
24 {
25 int x,y;
26 x = qrand()% parentScene->width();
27 y = qrand()% parentScene->height();
28 int r,g,b;
29 r = qrand() % 255;
30 g = qrand() % 255;
31 b = qrand() % 255;
32 ((MainWindow*)(this->parent()))->painterLock.lock();
33 QPainter painter;
34 painter.begin(parentScene);
35 QPen m_pen(QColor(r,g,b));
36 painter.setPen(m_pen);
37 switch(shape)
38 {
39 case 0:
40 painter.drawEllipse(x,y,(qrand() % 10) * 10,(qrand() % 10) * 10);
41 break;
42 case 1:
43 painter.drawRect(qrand() % parentScene ->width(),qrand() % parentScene->height(),(qrand()%10)* 15,(qrand()%10)* 15);
44 break;
45 case 2:
46 painter.drawLine(x-50,y,x+50,y);
47 painter.drawLine(x-50,y,x,y- 50);
48 painter.drawLine(x,y-50,x + 50,y);
49 default:
50 break;
51 }
52 painter.end();
53 ((MainWindow*)(this->parent()))->painterLock.unlock();
54 ((MainWindow*)(this->parent()))->update();
55 this->msleep(100);
56 }
57 }
注意在run()函数中，当对QImage操作时，使用到QMutex对象的lock，当绘图完成之后进行unlock()。
主工程代码：
1 #ifndef MAINWINDOW_H
2 #define MAINWINDOW_H
3 #include "ui_mainwindow.h"
4 #include <QMainWindow>
5
6 namespace Ui {
7 class MainWindow;
8 }
9 #include"drawthreading.h"
10 #include <QMutex>
11 class MainWindow : public QMainWindow
12 {
13 Q_OBJECT
14
15 public:
16 explicit MainWindow(QWidget *parent = 0);
17 ~MainWindow();
18
19 private:
20 Ui::MainWindow ui;
21 public:
22 DrawThread drawTriangleThread;
23 DrawThread drawEcllipseThread;
24 DrawThread drawRectThread;
25 QImage* m_image;
26 QMutex painterLock;
27 void paintEvent(QPaintEvent*);
28 void timerEvent(QTimerEvent* event);
29 };
30
31 #endif // MAINWINDOW_H
1 #include "mainwindow.h"
2 #include "ui_mainwindow.h"
3 #include <QThread>
4 #include <QImage>
5 #include <QPainter>
6 MainWindow::MainWindow(QWidget *parent) :
7 QMainWindow(parent)
8 {
9 ui.setupUi(this);
10 this->setAutoFillBackground(true);
11 m_image = new QImage(1024,768,QImage::Format_RGB32);
12 QPainter painter(m_image);
13 QBrush fillBrush(QColor(255,255,255));
14
15 painter.fillRect(0,0,1024,768,fillBrush);
16 this->startTimer(10000);
17
18 drawEcllipseThread.SetShape(0);
19 drawEcllipseThread.setParent(this);
20 drawEcllipseThread.start();
21
22 drawRectThread.SetShape(1);
23 drawRectThread.setParent(this);
24 drawRectThread.start();
25
26 drawTriangleThread.SetShape(2);
27 drawTriangleThread.setParent(this);
28 drawTriangleThread.start();
29 }
30
31 MainWindow::~MainWindow()
32 {
33
34 if (drawEcllipseThread.isRunning())
35 {
36 drawEcllipseThread.quit();
37 drawEcllipseThread.wait();
38 }
39 if (drawRectThread.isRunning())
40 {
41 drawRectThread.quit();
42 drawRectThread.wait();
43 }
44 if (drawTriangleThread.isRunning())
45 {
46 drawTriangleThread.quit();
47 drawTriangleThread.wait();
48 }
49 if (m_image)
50 {
51 delete m_image;
52 m_image = NULL;
53 }
54 }
55
56 void MainWindow::paintEvent(QPaintEvent*)
57 {
58 QPainter painter(this);
59 painter.drawImage(0,0,*m_image);
60
61 }
62 void MainWindow::timerEvent(QTimerEvent* event)
63 {
64 QPainter painter(m_image);
65 QBrush fillBrush(QColor(255,255,255));
66 painter.fillRect(0,0,1024,768,fillBrush);
67 }
我们在Qt帮助中查看QMutex,
The QMutex class provides access serialization between threads.
The purpose of a QMutex is to protect an object, data structure or section of code so that only one thread can access it at a time (this is similar to the Java synchronized keyword). It is usually best to use a mutex with a QMutexLocker since this makes it easy to ensure that locking and unlocking are performed consistently.
翻译过来，大致意思是，QMutex提供提供线程之间访问顺序化。QMutex目的是保护一个对象，数据结构或者一段代码以至于同一时间只能有一个线程访问。（与java中的关键字synchroized的类似）。Qt中的建议是使用QMutexLocker代替QMutex为了更容易的加锁、解锁。使用QMutexLocker对以上的代码进行调整，如下：
void DrawThread::run()
{
QImage* parentScene = ((MainWindow*)(this->parent()))->m_image;
//注意这里，使用QMutexLocker
QMutexLocker locker(&((MainWindow*)(this->parent()))->painterLock);
while(true)
{
int x,y;
x = qrand()% parentScene->width();
y = qrand()% parentScene->height();
int r,g,b;
r = qrand() % 255;
g = qrand() % 255;
b = qrand() % 255;
//((MainWindow*)(this->parent()))->painterLock.lock();
QPainter painter;
painter.begin(parentScene);
QPen m_pen(QColor(r,g,b));
painter.setPen(m_pen);
switch(shape)
{
case 0:
painter.drawEllipse(x,y,(qrand() % 10) * 10,(qrand() % 10) * 10);
break;
case 1:
painter.drawRect(qrand() % parentScene ->width(),qrand() % parentScene->height(),(qrand()%10)* 15,(qrand()%10)* 15);
break;
case 2:
painter.drawLine(x-50,y,x+50,y);
painter.drawLine(x-50,y,x,y- 50);
painter.drawLine(x,y-50,x + 50,y);
default:
break;
}
painter.end();
//((MainWindow*)(this->parent()))->painterLock.unlock();
((MainWindow*)(this->parent()))->update();
this->msleep(100);
}
}
至此，QMutex的方法已经讲诉完了，总之,QMutex提供提供线程之间访问顺序化。QMutex目的是保护一个对象，数据结构或者一段代码以至于同一时间只能有一个线程访问。
时间： 2024-12-25 23:27:12