How to wait for a boolean without looping (using any kind of wait / semaphore / event / mutex, etc)

Question

I need to stop a thread until another thread sets a boolean value and I don't want to share between them an event.

What I currently have is the following code using a Sleep (and that's the code I want to change):

while (!_engine.IsReadyToStop())
{
    System.Threading.Thread.Sleep(Properties.Settings.Default.IntervalForCheckingEngine); 
}

Any ideas?

EDIT TO CLARIFY THINGS:

There is an object called _engine of a class that I don't own. I cannot modify it, that's why I don't want to share an event between them. I need to wait until a method of that class returns true.

Solution 1

SpinWait.SpinUntil is the right answer, regardless where you're gonna place this code. SpinUntil offers "a nice mix of spinning, yielding, and sleeping in between invocations".

Solution 2

If you are using C# 4.0, you can use:

Task t = Task.Factory.StartNew (() => SomeCall(..));
t.Wait();

By using Task.Wait method.

If you have more than one task run one after another, you can use Task.ContinueWith:

 Task t = Task.Factory.StartNew (() =>SomeCall(..)).
                                ContinueWith(ExecuteAfterThisTaskFinishes(...);
 t.Wait();

Solution 3

declare as

 AutoResetEvent _ReadyToStop = new AutoResetEvent(false);

and use as

 _ReadyToStop.WaitOne();

and

 _ReadyToStop.Set();

For more info see the Synchronization Primitives in .Net

Comments

[Tudor]

Why don't you want to share an event? There are two ways to do what you want: events or spinning.

[L.B]

You want to share a boolean value but not an event. Why? What is the difference?

[L.B]

I need to wait until a method of that class returns true. So what do you expect from us. Just loop as you already do.

[Ignacio Soler Garcia]

The title of the question is crystal clear I think: How to wait for a boolean without looping. If that cannot be done a "you cant'" will be the right answer. I'm not sure if this can or cannot be done.

[L.B]

OK you get the answer. No you can't

[Tudor]

@SoMoS: But what is going on inside that method? Is it spawning a thread?

[Ignacio Soler Garcia]

@Tudor: yeah, the engine runs on its own thread.

[Tudor]

Well if you cannot change that class and the only way it communicates termination is with that boolean then I'm afraid you can't do anything but this spinning.

[Martin James]

It would have been friendlier if the 'engine' thing had called an 'OnReadyToStop' event, instead of supplying this silly polling method, but you seem to be stuck with it. Really need an engine rebuild..

[Ignacio Soler Garcia]

Ready to stop is a method that returns a boolean and that method is used at several places, that's why I said that I don't want to share an event between them, so as far as I know your answer is not valid.

[L.B]

@SoMoS funny, then use another name

[Tudor]

What is the point of spawning a task and immediately joining it? And I don't think this was the OP's question.

[David W]

ReadyToStop is just the name he gave to the AutoResetEvent variable.

[Tigran]

@Tudor: I had a doubt on this too, so add add also explanation about ContinueWith

[Ignacio Soler Garcia]

I hope that now the question is more clear. My bad if it was not at the fist shot.

[Ignacio Soler Garcia]

I hope that now the question is more clear. My bad if it was not at the fist shot.

[Ignacio Soler Garcia]

As the problem is not waiting a task to end but waiting until a value is set I think the proposed solution is not applicable. Makes sense?

[Tigran]

@SoMoS: as your request is only waiting for the bollean change, that answer of L.B makes more sence. Just at the moment you set the boolean, Set event from the thread.

[Tigran]

@SoMoS: like stuff for readin can have a look on really comprehensive guide: Threading in C# of LinqPad creator.

[Ignacio Soler Garcia]

Not as good as a lock but seems the only possible way of doing it currently and much better that manually waiting.

[StaceyGirl]

.NET has monitors separate condition variable is not needed, unless you need to share multiple condition variables with the same lock, but I doubt this is what OP needs.