C++ QThread：线程仍在运行时被销毁？

QThread: Destroyed while thread is still running?

提问by The Man

I would like to start my QThreadwhen I push on button Run. But the compiler outputs following error:

QThread当我按下按钮Run时，我想开始我的。但是编译器输出以下错误：

QThread: Destroyed while thread is still running
ASSERT failure in QThread::setTerminationEnabled(): "Current thread was not started with QThread.", file thread\qthread_win.cp.

I don't know what is wrong with my code.

我不知道我的代码有什么问题。

Any help would be appreciated.

任何帮助，将不胜感激。

Here is my code:

这是我的代码：

SamplingThread::SamplingThread( QObject *parent):
   QwtSamplingThread( parent ),
   d_frequency( 5.0 )
{
   init();
}

MainWindow::MainWindow( QWidget *parent ):
QMainWindow( parent )
{.......
  .....
   run= new QPushButton ("Run",this);
   stop= new QPushButton("Stop",this);
   connect(run, SIGNAL(clicked()),this, SLOT (start()));
}

MainWindow::start
{
   SamplingThread samplingThread;
   samplingThread.setFrequency( frequency() );
   samplingThread.start();
}

int main( int argc, char **argv )
{
   QApplication app( argc, argv );
   MainWindow window;
   window.resize( 700, 400 );
   window.show();
   bool ok = app.exec();
   return ok;
}

回答by Erik

As the error message states: QThread: Destroyed while thread is still running. You are creating your SamplingThreadobject inside the MainWindow::startmethod but it goes out of scope (i.e. is destroyed) when that method terminates. There are two easy ways that I see:

正如错误消息所述：QThread: Destroyed while thread is still running. 您正在方法SamplingThread内部创建对象，MainWindow::start但是当该方法终止时它超出范围（即被销毁）。我看到有两种简单的方法：

1. You make your SamplingThreada member of your MainWindowso its lifetime is the same as for the MainWindowinstance

2. You use a pointer, i.e. you create the SamplingThreadusing

   SamplingThread *samplingThread = new SamplingThread;

1. 您使您成为您SamplingThread的成员，MainWindow因此其生命周期与MainWindow实例相同

2. 您使用指针，即您创建SamplingThread使用

   SamplingThread *samplingThread = new SamplingThread;

Does this help?

这有帮助吗？

Edit: to illustrate the two cases, a very crude example to show the two cases

编辑：为了说明这两种情况，一个非常粗略的例子来展示这两种情况

#include <iostream>
#include <QApplication>
#include <QThread>

class Dummy
{
public:
  Dummy();
  void start();
private:
  QThread a;
};

Dummy::Dummy() :
  a()
{
}


void Dummy::start()
{
  a.start();
  QThread *b = new QThread;
  b->start();

  if( a.isRunning() ) {
    std::cout << "Thread a is running" << std::endl;
  }
  if( b->isRunning() ) {
    std::cout << "Thread b is running" << std::endl;
  }
}

int main(int argc, char** argv)
{
  QApplication app(argc,argv);
  Dummy d;
  d.start();
  return app.exec();
}

回答by Marek R

This is basics of C++! You are creating local object of QThreadon stack not on heap, so it gets destroys immediately when you leave method MainWindow::start.

这是C++的基础！您正在QThread堆栈上而不是在堆上创建本地对象，因此当您离开 method 时它会立即销毁MainWindow::start。

It should be done like that:

应该这样做：

MainWindow::MainWindow( QWidget *parent ):
QMainWindow( parent )
{
   ...

   samplingThread = SamplingThread(this);
   samplingThread->setFrequency( frequency() );

   run= new QPushButton ("Run",this);
   stop= new QPushButton("Stop",this);
   connect(run, SIGNAL(clicked()), samplingThread, SLOT(start()));
}

MainWindow::~MainWindow() {
   samplingThread->waitFor(5000);
}

回答by Ulrich Eckhardt

There are two different "threads" involved: One is the actual thread, the other is the C++ object representing it (and to be correct, there is another thread from which this code is started in the first place).

涉及两个不同的“线程”：一个是实际线程，另一个是表示它的 C++ 对象（正确地说，还有另一个线程，该代码首先从该线程开始）。

The error just says that the thread is still running at the point where the C++ object representing it is destroyed. In your code, the reason is that the QThread instance is local to start(). Maybe you want to store the QThread in a member.

该错误只是表明线程仍在表示它的 C++ 对象被销毁的点上运行。在您的代码中，原因是 QThread 实例是start(). 也许您想将 QThread 存储在成员中。