除了调用thread.Join（）之外，如何等待线程完成运行？ [英] How can I wait for a thread to finish running other than by calling thread.Join()?

问题描述

我正在一个项目中，该方法是从库中可用的应用程序中调用方法的。

I am working on a project where the methods are called from the an application which is available with the library.

我的按钮单击事件中包含以下代码：

I have the below code in my button click event:

Thread thread = new Thread(new ThreadStart(AddPics));
thread.Priority = ThreadPriority.Highest;
thread.Start();
execute();

但是在运行示例时，执行点始终移至执行位置。如何使程序首先执行 AddPics 方法。我已经尝试过 thread.Join（）并成功了，但是我想知道是否还有其他方法可以实现这一目标。

But while running the sample always the execution point moves to the execute. How to make the program to execute the AddPics method first. I have tried thread.Join() and it worked, but I want to know if there is any other way to achieve this.

推荐答案

您可以使用 Join 或 AutoResetEvent 等待添加图片线程修饰符，但是您不应该使用答案中稍后解释的任何一种方法。

You can use Join or AutoResetEvent to wait until add picture thread finishes, But you should not use either as explained later on the answer.

您可以通过使用<$获得相同的结果c $ c> AutoResetEvent 代替 Join ；它允许您设置阻止通知，因此请在调用 execute（）方法之前进行阻止，并且仅在 AddPics 时继续进行线程完成其工作：

You can achieve the same results by using AutoResetEvent as alternative to Join; it allows you to setup a blocking-notification, so block before calling the execute() method and only proceed when AddPics thread finishes its job:

private AutoResetEvent _finishAddPicsNotifier = new AutoResetEvent(false);

private void OnMyButton_Click(object sender, EventArgs e)
{
    //.....
    new Thread(AddPics)
    {
        Priority = ThreadPriority.Highest,
        IsBackground = true, //will explain later
    }.Start();

    _finishAddPicsNotifier.WaitOne();//this will block until receive a signal to proceed
    execute();//this method will only be called after the AddPics method finished
    /.....
}

private void AddPics()
{
    try{
        //.......
    }
    finally{
        _finishAddPicsNotifier.Set();//when finished adding the pictures, allow the waiting method to proceed
    }
}

注意：设置 IsBackground = true 表示该线程是后台线程，因此不会阻止应用程序终止。在此处中了解更多信息。

Note: Set IsBackground = true to indicates that thread is a background thread so it will not prevent the application from terminating. read more about background thread here.

问题：

• 由于您使用的是单击按钮以运行该线程，则应添加某种机制以防止多次单击以多次运行该代码。


• 在调用<$时，您还将阻塞UI线程c $ c> Join（）或 _finishAddPicsNotifier.WaitOne（）。

• Since you are using a button click to run the thread, you should add some mechanism to prevent multi-clicks at the same time to run the code multiple time.
• You are also blocking the UI thread when call Join() or _finishAddPicsNotifier.WaitOne().

要解决所有这些问题，一个好的设计是定义一个方法 OnFinishAddingPictures ，并在添加完图像后立即调用它，在此新方法调用 execute（）中，还应该从按钮单击中删除先前的 execute（）调用：

To fix all of that, a good design is to define a method OnFinishAddingPictures and call it whenever finish adding images, inside this new method call execute(), you should also remove the previous execute() call from button click:

private readonly object _oneAddPicturesLocker = new object();

private void OnMyButton_Click(object sender, EventArgs e)
{
    //.....
    new Thread(AddPics)
    {
        Priority = ThreadPriority.Highest,
        IsBackground = true,
    }.Start();
}

private void AddPics()
{
    if (Monitor.TryEnter(_oneAddPicturesLocker))
    {
        //we only can proceed if no other AddPics are running.
        try
        {
            //.....

            OnFinishAddingPictures();
        }
        finally
        {
            Monitor.Exit(_oneAddPicturesLocker);
        }
    }
}

private void OnFinishAddingPictures()
{
    execute();
}

注意：

• 我们使用这种机制摆脱了阻塞。


• 我们确定只有一个调用 AddPics 会立即执行。


• 始终记得检查 InvokeRequired 并使用 control.Invoke（/*..*/)每当通过不是UI线程的线程访问表单或控件方法和属性时。

• We get rid of the blocking using this mechanism.
• We are sure One and Only one call to the AddPics are executed at a moment.
• Always remember to check InvokeRequired and use control.Invoke(/*..*/) whenever accessing form or control methods and properties from a thread that is not the UI thread.

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