Notify parent thread when child has performed a certain action [C#]

Question

I have a parent thread (non-UI) which creates some child threads to do some jobs - at some point the parent must wait for certain tasks to be completed by the child thread - this does not mean the child is finished but only that it has reached a certain point and the parent can now continue processing ...

To illustrate please refer to the code below, obviously this isn't what my children do but it shows what I am trying to accomplish. Recall that none of these are UI threads...

// Parent Thread
Thread childThread = new Thread(new ThreadStart(Manage));
childThread.IsBackground = true;
childThread.Name = "NamedPipe Manager";
childThread.Start();

while (true)
{
... do some work ...

// wait for signal from MainThread to proceed //

... do more work
}


// Child Thread
private void Manage()
{
... do some work ...
... call some functions ...

// SIGNAL TO PARENT THAT IT CAN CONTINUE //

... do more work ...
... call more functions ...
}

Any one have any suggestions on how I can accomplish this task in a thread-safe manner? Any help would be much appreciated. Thanks,

Answer 1

You can do this using a WaitHandle (I would add the usual code sample, but the example given in MSDN is almost exactly what you want)

Answer 2

If there's a single child thread you can use a ManualResetEvent:

var signal = new ManualResetEvent(false);

// child thread: signal to parent that it can continue
signal.Set();

// parent thread: wait for signal from child thread to proceed
signal.WaitOne();

If there's more than one child thread you can use a Semaphore:

var semaphore = new Semaphore(0, numberOfChildThreads);

// child thread: signal to parent that it can continue
semaphore.Release();

// parent thread: wait for signal from each child thread to proceed
for (int i = 0; i < numberOfChildThreads; i++)
{
    semaphore.WaitOne();
}

Answer 3

Is there a reason you're using explicit threads instead of BackgroundWorker? BackgroundWorker has built-in facilities for communicating progress back to the UI thread.