QT之使用QMutex/ QMutexLocker互斥量同步线程小例子

    接上一篇，在多线程中基本上都需要解决线程同步问题，本篇文章主要将介绍如何使用QMutex/ QMutexLocker互斥量来同步线程。

    首先，先回顾下Qt官网QThreads general usage介绍，其中有一段基本上介绍了其使用方法，如下：

    The main thing in this example to keep in mind when using a QThread is that it's not a thread. It's a wrapper around a thread object. This wrapper provides the signals, slots and methods to easily use the thread object within a Qt project. To use it,
prepare a QObject subclass with all your desired functionality in it. Then create a new QThread instance, push the QObject onto it using moveToThread(QThread*) of the QObject instance and call start() on the QThread instance. That's all. You set up the proper
signal/slot connections to make it quit properly and such, and that's all.

    现在，直接上售票的小例子：

    Step1. 按Qt介绍的用法：先创建一个继承QObject的类，把要执行的函数包装进里面：

.h 文件代码如下：

#ifndef TICKETSELLER_H
#define TICKETSELLER_H

#include <QObject>
#include <QThread>
#include <QMutex>
#include <string>

class TicketSeller : public QObject
{
public:
TicketSeller();

~TicketSeller();

public slots:
void sale();

public:
int* tickets;

QMutex* mutex;

std::string name;
};

#endif // TICKETSELLER_H

.cpp 文件代码如下：

#include "ticketseller.h"
#include <iostream>

TicketSeller::TicketSeller()
{
tickets = 0;
mutex = NULL;
}

TicketSeller::~TicketSeller()
{

}

void TicketSeller::sale()
{
while((*tickets) > 0)
{
mutex->lock();
std::cout << name << " : " << (*tickets)-- << std::endl;
mutex->unlock();
}

/*while((*tickets) > 0)
{
QMutexLocker locker(mutex);
std::cout << name << " : " << (*tickets)-- << std::endl;
locker.unlock();
}*/
}

    Step2. 按Qt介绍的用法：创建一个实例，使用moveToThread将对象移至QThread内，并连接信号槽，最后调用start()方法：
main.cpp 文件代码如下：

#include <QCoreApplication>
#include <QMutex>
#include <QThread>
#include <string>
#include "ticketseller.h"

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

int ticket = 100;
QMutex mutex;

/*创建设置线程1*/
//创建线程1
QThread t1;
TicketSeller seller1;
//设置线程1
seller1.tickets = &ticket;
seller1.mutex = &mutex;
seller1.name = "seller1";
//将对象移动到线程
seller1.moveToThread(&t1);

/*创建设置线程2*/
//创建线程2
QThread t2;
TicketSeller seller2;
seller2.tickets = &ticket;
seller2.mutex = &mutex;
seller2.name = "seller2";
//将对象移动到线程
seller2.moveToThread(&t2);

QObject::connect(&t1, &QThread::started, &seller1, &TicketSeller::sale);
QObject::connect(&t2, &QThread::started, &seller2, &TicketSeller::sale);

t1.start();
t2.start();

return a.exec();
}


    QT 中使用 QMutex/ QMutexLocker 比Window API CreateMutex 配合 WaitForSingleObject 同步线程要简单得多。