non busy waiting for object initialization

Question

I would like to do a non busy waiting for a variable to become non-null:

while (true)
{
    if (myStaticVar != null)
    {
        break;
    }
}

myStaticVar.DoSomething();

The myStaticVar could be set any time by any thread.

I am stuck to .net 4, so i can not use async/await.

Is `myStaticVar` set by another thread? If so use signaling. If not you have to explain a bit more. — Brian Rasmussen, Nov 03 '15 at 16:21
[Duplicate?](http://stackoverflow.com/questions/9110472/using-async-await-on-net-4) if you have VS 2012 you can also use [Microsoft Async 1.0.168](https://www.nuget.org/packages/Microsoft.Bcl.Async) — Tim Schmelter, Nov 03 '15 at 16:24
You can use this http://www.nuget.org/packages/microsoft.bcl.async To use Async in .net framework 4 — kevinrodriguez-io, Nov 03 '15 at 16:25

score 0 · Answer 1 · edited May 23 '17 at 12:23

The correct solution would be to let your threads communicate via a .NET synchronization primitive such as AutoResetEvent. Lots of examples can be found on SO, for example, here.

That said, manual thread synchronization is a hard problem and easy to get wrong. If your code is not time-critical and you prefer the simplicity of "busy waiting", don't forget to yield processor time while doing so. Either add some Thread.Sleep in your loop or use SpinWait.SpinUntil.

score 0 · Answer 2 · answered Nov 03 '15 at 16:43

You could convert your variable into a property and use the set accessor to call a delegate.

void Main()
{
    _someAction = () => Console.WriteLine("Hello world!");

    myStaticVar = 20;
}

private static Int32 _myStaticVar;
private static Action _someAction;

public static Int32 myStaticVar 
{
    get
    {
        return _myStaticVar;
    }
    set
    {
        _myStaticVar = value;

        if (_someAction != null)
            _someAction();
    }
}

non busy waiting for object initialization

2 Answers2