I can see five options available:
1. Thread.Join
As with Mitch’s answer. But this will block your UI thread, however you get a Timeout built in for you.
2. Use a WaitHandle
ManualResetEvent
is a WaitHandle
as jrista suggested.
One thing to note is if you want to wait for multiple threads: WaitHandle.WaitAll()
won’t work by default, as it needs an MTA thread. You can get around this by marking your Main()
method with MTAThread
– however this blocks your message pump and isn’t recommended from what I’ve read.
3. Fire an event
See this page by Jon Skeet about events and multi-threading. It’s possible that an event can become unsubcribed between the if
and the EventName(this,EventArgs.Empty)
– it’s happened to me before.
(Hopefully these compile, I haven’t tried)
public class Form1 : Form { int _count; void ButtonClick(object sender, EventArgs e) { ThreadWorker worker = new ThreadWorker(); worker.ThreadDone += HandleThreadDone; Thread thread1 = new Thread(worker.Run); thread1.Start(); _count = 1; } void HandleThreadDone(object sender, EventArgs e) { // You should get the idea this is just an example if (_count == 1) { ThreadWorker worker = new ThreadWorker(); worker.ThreadDone += HandleThreadDone; Thread thread2 = new Thread(worker.Run); thread2.Start(); _count++; } } class ThreadWorker { public event EventHandler ThreadDone; public void Run() { // Do a task if (ThreadDone != null) ThreadDone(this, EventArgs.Empty); } } }
4. Use a delegate
public class Form1 : Form { int _count; void ButtonClick(object sender, EventArgs e) { ThreadWorker worker = new ThreadWorker(); Thread thread1 = new Thread(worker.Run); thread1.Start(HandleThreadDone); _count = 1; } void HandleThreadDone() { // As before - just a simple example if (_count == 1) { ThreadWorker worker = new ThreadWorker(); Thread thread2 = new Thread(worker.Run); thread2.Start(HandleThreadDone); _count++; } } class ThreadWorker { // Switch to your favourite Action<T> or Func<T> public void Run(object state) { // Do a task Action completeAction = (Action)state; completeAction.Invoke(); } } }
If you do use the _count method, it might be an idea (to be safe) to increment it using
Interlocked.Increment(ref _count)
I’d be interested to know the difference between using delegates and events for thread notification, the only difference I know are events are called synchronously.
5. Do it asynchronously instead
The answer to this question has a very clear description of your options with this method.
Delegate/Events on the wrong thread
The event/delegate way of doing things will mean your event handler method is on thread1/thread2 not the main UI thread, so you will need to switch back right at the top of the HandleThreadDone methods:
// Delegate example if (InvokeRequired) { Invoke(new Action(HandleThreadDone)); return; }