QThread 采用moveToThread方式实现多线程。 线程本身、connect关联的槽函数、connect关联的lambda对象分别运行在哪个线程中。

Qt如何实现多线程：https://www.cnblogs.com/azbane/p/11372531.html

September 5，2019

先抛出几个问题，用问题来引导思维导向：

1、继承的QObject子类，和QThread对象，是在哪个线程创建的？（即：QObject子类对象和QThread对象的依附线程是哪个？）

2、QThread在哪个线程运行？

3、QObject::moveToThread( QThread )后，QThread 的信号(started/finished)关联的QObject子类对象的函数（槽函数）哪个线程运行？

4、QObject::moveToThread( QThread ) 后，QThread的信号(started/finished)关联的依附线程对象的槽函数在哪个线程运行？

5、信号和槽的新版本，用lambda表达式处理信号的情况（QThread的信号(started/finished)关联的lambda），lambda对象运行在哪个对象？

看起来很复杂，其实并不可怕：想知道对象在哪个线程运行，有两种方式可用

1：QThread::currentThreadId()  返回16进制的线程ID (#include<QThread>)

2：std::this_thread::get_id() 返回10进制的线程ID  （#include<iostream> #include <QThread>）

先给答案，再上例子说明， 最后给出遇到的错误情况。

上面跑出的5个问题的答案：

假定QObject子类对象和QThread对象都是在线程A中创建。

1、线程A。  调用std::this_thread::get_id

2、线程A。  调用QThread::currentThreadId， 需要由16进制转成10进制，再对比。

3、线程B。  假定线程id = B 。调用std::this_thread::get_id

4、线程A。  调用std::this_thread::get_id

5、线程B。  调用std::this_thread::get_id

例子主要信息说明：

类ShapeLayout:

　　　　　　有两个指针数据成员：GenerateGridFileWork * m_generateGridFileWork;   QThread * m_generateGridFileWorkThread;

　　　　　　有一个函数成员：MakeGrid， 函数里面创建两个指针数据成员。

                      m_generateGridFileWork->moveToThread(m_generateGridFileWorkThread);

　　　　　　GenerateGridFileWork::slotsWork
　　　　　　QThread::signals - started / finished

ShapeLayout.h
-----------------------------------------------------------
class ShapeLayout :  public QObject
{
  Q_OBJECT

public:
    void makeGrid();

public slots:
  void slotsThreadFininshed(); 

private:
    GenerateGridFileWork * m_GenerateGridFileWork = nullptr;
    QThread * m_GenerateGridFileWorkThread = nullptr;   
}

ShapeLayout.cpp 
-----------------------------------------------------------
void ShapeLayout::makeGrid()
{
    std::cout<<"ShapeLayout thread id is "<<std::this_thread::get_id()<<std::cout;  //问题-1
    m_GenerateGridFileWork  = new GenerateGridFileWork ;
    m_GenerateGridFileWorkThread  =  new QThread;

    m_GenerateGridFileWork->moveToThread(m_GenerateGridFileWorkThread);

    QObject::connect(m_GenerateGridFileWorkThread, &QThread::started, m_GenerateGridFileWork  , &GenerateGridFileWork::slotsWork);
    
    QObject::connect(m_GenerateGridFileWork, &GenerateGridFileWork::signalsWorkFinished, m_GenerateGridFileWorkThread, &QThread::quit);

    QObject::connect(m_GenerateGridFileWorkThread, &QThread::finished, this, &ShapeLayout::slotsThreadFininshed);
     
    QObject::connect(m_GenerateGridFileWorkThread, &QThread::started, []{
     std::cout<<"connect thread-started signals lambda object  thread id is"<<std::this_thread::get_id()<<std::cout; //问题-5
});

    QObject::connect(m_GenerateGridFileWorkThread, &QThread::finished, []{
    std::cout<<"connect thread-finishedsignals lambda object  thread id is"<<std::this_thread::get_id()<<std::cout;//问题-5

});

    std::cout<<"QThread thread id is "<<m_generateGridFileWorkThread->currentThreadId()<<std::cout; //问题-2 

    m_GenerateGridFileWorkThread->start();

}

void ShapeLayout::slotsThreadFininshed()
{
　　std::cout<<"connect slots function of the ShapeLayout attributable thread id is"<<std::this_thread::get_id()<<std::cout;//问题-4
}

GenerateGridFileWork.h
------------------------------------------------
class GenerateGridFileWork : public QObject
{
public slots:
       void slotsWork();

signals:
       void signalsWorkFinished();
}

GenerateGridFileWork.cpp
------------------------------------------------
void GenerateGridFileWork::slotsWork()
{
      std::cout<<"connect to slots function of QObject subObject thread id is "<<std::this_thread::get_id()<<std::cout;//问题-3

      emit   signalsWorkFinished();
} 

调用ShapeLayout::makeGrid()；　一切都知道啦，  自己去运行一遍吧

OK perfect...