是否应该使用Thread.Sleep（）检查进程是否仍在运行？

Question

As title says, I'm currently making a WPF application and I need to detect if an application is running and do something when it's closed. The way I'd thought of doing so is by running a separate Thread and checking every two seconds if the process is still running, something like this:

while(Process.GetProcessesByName(processName).Length != 0) {
    Thread.Sleep(2000);
}

//Do something

Would this be a good solution, is there any other way of doing this?

Thanks

Answer 1

Would this be a good solution?

No, because it would waste an entire thread for nearly nothing.

Better use a timer, in a WPF application preferrably a DispatcherTimer:

var timer = new DispatcherTimer { Interval = TimeSpan.FromSeconds(2) };

timer.Tick += (s, e) =>
{
    if (Process.GetProcessesByName(processName).Length > 0)
    {
        // ...
    }
};

timer.Start();

---

If there would be a lengthy operation to be performed off the UI thread, you could use an async Tick event handler that awaits a Task (which would run on a thread pool thread in the background):

var timer = new DispatcherTimer { Interval = TimeSpan.FromSeconds(2) };

timer.Tick += async (s, e) =>
{
    if (Process.GetProcessesByName(processName).Length > 0)
    {
        await Task.Run(() =>
        {
            // lengthy operation here which runs on a thread pool thread
        });

        // udate UI here
    }
};

timer.Start();

Answer 2

Since you are already dealing with Processes, I would suggest just using it directly to determine if it has exited. You can use the Exited event handler for your code. So, for instance:

foreach (var process in Process.GetProcessesByName(processName))
{
  process.Exited += new EventHandler(DoSomething);
}

…

public void DoSomething(object sender, System.EventArgs e)
{
  // do something
}

This will call DoSomething when the process with that name ends.

Answer 3

You could use a System.Timers.Timer that performs the check every x seconds:

public sealed partial class Window1 : Window, IDisposable
{
    private readonly System.Timers.Timer _timer = new System.Timers.Timer(TimeSpan.FromSeconds(2).TotalMilliseconds);

    public Window1()
    {
        InitializeComponent();
        _timer.Elapsed += _timer_Elapsed;
        _timer.Start();
    }

    private void _timer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
    {
        if (Process.GetProcessesByName("processName...").Length == 0)
        {
            _timer.Stop();
            _timer.Dispose();
            //do something...
        }
    }


    public void Dispose()
    {
        _timer.Dispose();
    }
}

Unlike the Tick event of a DispatcherTimer , the Elapsed event of a Timer is always queued for execution on a thread pool thread.

From the docs :

If a System.Timers.Timer is used in a WPF application, it is worth noting that the System.Timers.Timer runs on a different thread than the user interface (UI) thread...Reasons for using a DispatcherTimer as opposed to a System.Timers.Timer are that the DispatcherTimer runs on the same thread as the Dispatcher and a DispatcherPriority can be set on the DispatcherTimer .