Message queue for cross thread sync

Question

public class WmSync : IDisposable
{
    public WmSync()
    {
        var sync = new Control();
        sync.Handle.GetHashCode(); // ensure handle is created
        _sync = sync;
        Thread.MemoryBarrier();
    }

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

    public void BeginInvoke(Action action)
    {
        _sync.BeginInvoke(action);
    }

    public void Invoke(Action action)
    {
        _sync.Invoke(action);
    }

    public bool InvokeRequired
    {
        get { return _sync.InvokeRequired; }
    }

    private readonly Control _sync;
}

The idea is to create this object in the main thread and use it from background threads to execute pieces of code in the main thread.

For example:

// somewhere in the very beginning of the program, in the main thread
static WmSync SyncQueue = new WmSync();

// somewhere in a background thread
SyncQueue.Invoke(
    () =>
    {
        if (_settingsForm != null)
            _settingsForm.Show();
    });

This is just an artificial sample, but it should give you idea. Is this code thread safe?

Answer 1

Thread.MemoryBarrier()

What do you expect the call to Thread.MemoryBarrier() will help your code ?

What does Thread.MemoryBarrier do ? It prevents that the compiler and the hardware subtly transform a program’s memory operations.

So basically for your code it ensures that then following instructions will be executed in the order they are written.

var sync = new Control();
sync.Handle.GetHashCode(); // ensure handle is created
_sync = sync;  

Thread safety

To answer "Is this code thread safe ?", you first need to set your definition of thread safety aka what does thread safety means for you. See also what-is-this-thing-you-call-thread-safe

General

• the code is lacking a EndInvoke() which should be integrated.

• you are misusing a Control to access the main (ui) thread of an application.

• wouldn't a SynchronizationContext be a better fit here ?

  See also: https://stackoverflow.com/a/20300351/2655508