如何一遍又一遍地启动和停止后台线程？

Question

I have c# app that has UI and background threads. Based on user input I like to stop and start the background thread. I have two options here as I see:

1) totally stop and then start background thread as new thread ( I have not been able to this. I keep getting my process ended message)

2) Pause the background thread until user click run again.

Here is the code that I call again after bw.CancelAsync();

    private void StartBackgroundWorker()
    {
        bw = new BackgroundWorker();
        bw.WorkerReportsProgress = true;
        bw.WorkerSupportsCancellation = true;
        bw.DoWork += bw_DoWork;
        bw.RunWorkerCompleted += bw_RunWorkerCompleted;
        bw.RunWorkerAsync("Background Worker");
    }

Answer 1

you can't start and stop a background worker like that, but in your DoWork event, you can have it ask whether it should execute or wait.

you can also subclass BackgroundWorker (override the OnDoWork() method), and add start/pause methods to it that toggle a private wait handle, which is much nicer than having your UI know about the ManualResetEvent.

//using System.Threading;

//the worker will ask this if it can run
ManualResetEvent wh = new ManualResetEvent(false);

//this holds UI state for the start/stop button
bool canRun = false;

private void StartBackgroundWorker()
{
    bw = new BackgroundWorker();
    bw.WorkerReportsProgress = true;
    bw.WorkerSupportsCancellation = true;
    bw.DoWork += bw_DoWork;
    bw.RunWorkerCompleted += bw_RunWorkerCompleted;
    bw.RunWorkerAsync("Background Worker");
}


void bw_DoWork(object sender, DoWorkEventArgs e)
{
     while(true) 
     {
          //it waits here until someone calls Set() on wh  (via user input)
          // it will pass every time after that after Set is called until Reset() is called
          wh.WaitOne()

         //do your work

     }
}


//background worker can't start until Set() is called on wh
void btnStartStop_Clicked(object sender, EventArgs e)
{
    //toggle the wait handle based on state
    if(canRun)
    {
        wh.Reset();
    }
    else {wh.Set();}

    canRun= !canRun;
    //btnStartStop.Text = canRun ? "Stop" : "Start";
}

Answer 2

You can always abort a thread and catch the ThreadAbortedException. Im not sure if this is the most neat solution since an exception causes a lot of overhead but i think it is better than spreading WaitOne in the code like Dan suggested.

Another solution is to inherit from the thread class, and add a function to this class that stops or pauses the thread. This way you can hide the details of the implementation.