为什么这种关闭工作线程的方法不起作用？ [英] Why doesn't this method of closing a worker thread work?

问题描述

我有一个MFC应用程序，其GUI有一个开始和一个停止按钮。开始按钮定期调用我想在后台运行的功能。我的解决方案是使用 SetTimer 函数定期调用 OnTimer 函数。然后，此函数使用 AfxBeginThread 创建一个线程，然后填充我作为参数传递给线程的结构。所有这一切都很好。



我现在想做的是让停止按钮结束线程。我已经阅读了 TerminateThread ，但它看起来风险太大了。由于我想从另一个线程关闭工作线程，我知道我不能使用 AfxEndThread ，但我想知道为什么以下解决方案不起作用。 />


我尝试了什么：



我创建了 int 变量名为 count 并在按下start时将其设置为 0 并设置每当按下停止时它都 1

我传入的结构 AfxBeginThread 看起来像这样

I have an MFC application whose GUI has a start and a stop button. The start button calls a function which I want to run in the background, periodically. My solution was to use the SetTimer function to call the OnTimer function at regular intervals. This function then creates a thread using AfxBeginThread and then populates the structure that I pass to the thread as a parameter. All this works just fine.

What I would like to do now is the make the stop button end the thread. I have read about TerminateThread but it seems too risky. Since I want to close the worker thread from another thread, I know I can't use AfxEndThread, but I wanted to know why the following solution doesn't work.

What I have tried:

I created an int variable called count and set it to 0 whenever start is pressed, and set it to 1 whenever stop is pressed.
The structure I am passing into AfxBeginThread looks like this

typedef struct THREADSTRUCT
            {
            MyGUIDlg*    _this;
	       int          flag;
            //you can add here other parameters you might be interested on
           } THREADSTRUCT;

当开始时是按下 SetTimer 函数被调用，其回调函数定义如下：

When start is pressed the SetTimer function is called, whose callback function is defined like this:

void MyGUIDlg::OnTimer(UINT_PTR nIDEvent)
{
	THREADSTRUCT* _param = new THREADSTRUCT;
	_param->_this=this;
	_param->flag = count;
	AfxBeginThread(StartThread, _param);	
	CDialog::OnTimer(nIDEvent);
}

在我的StartThread功能中，我添加了以下内容：

In my StartThread function I have added the following:

UINT MyGUIDlg::StartThread(LPVOID param)
{
    THREADSTRUCT *ts = (THREADSTRUCT*)param;
    if((ts->flag)==1)
	{
		//Use AfxEndThread to close this thread
	}

	return 0;
}

但这似乎不起作用，有什么想法？

But this doesn't seem to work, any thoughts why?

推荐答案

工作线程通常包含一个循环，用于检查停止条件：

A worker thread usually contains a loop where it checks for a stop condition:

UINT MyGUIDlg::StartThread(LPVOID param)
{
    THREADSTRUCT *ts = (THREADSTRUCT*)param;
    while (!ts->flag)
    {
        // Perform operations here
        // May also break the loop for self termination
    }
    // Thread is closed when it returns or when
    //  AfxEndThread() is called.
    // When m_bAutoDelete is TRUE, the thread object is deleted.
    return 0;
}

上面轮询一个共享变量变量来检查线程是否应该终止。更好的解决方案是使用某种信号（事件）。



但是在你的例子中没有循环，线程总是立即关闭。



我建议阅读有关工作线程的信息。一篇陈旧但非常好的文章是使用工作线程 [ ^ ]。另请参见使用C ++和MFC进行多线程处理 [ ^ ]。

The above polls a shared variable variable to check if the thread should terminate. A better solution is using some kind of signals (events).

But in your example there is no loop and the thread is always closed immediately.

I suggest to read about worker threads. An old but very good article is Using Worker Threads[^]. See also Multithreading with C++ and MFC[^] in the MSDN.

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