如何使后台工作线程之间的事件在自己的上下文中执行

Question

This question was asked 11 years ago but the answers all assumed Winform/WPF. I'd like to ask it again but clarify these are two backgroundworker threads.

I'd like to have two Threads. Let's call them:

• Thread A (Thread.CurrentThread.ManagedThreadId is 16)
• Thread B (Thread.CurrentThread.ManagedThreadId is 18);

Thread A fires an event and Thread B listens to this event. When the Thread B event listener (delegate) is executed, it's executed with the Thread A's context (16).

What I'd like to do is be able to fire event in Thread A (16) and the delegate code execute under the context of Thread B (18).

From what I've seen there is no SynchronizationContext available in this scenario.

How can I do that?

Thank you for your help.

Answer 1

You could consider using Microsoft's Reactive Framework (aka Rx) - NuGet System.Reactive and add using System.Reactive.Linq; - so that you could take advantage of the EventLoopScheduler class. This class creates a single thread that you can schedule tasks on in a variety of ways.

Given private EventLoopScheduler _eventLoopScheduler = new EventLoopScheduler(); I can do this to run code on the specific thread:

IDisposable scheduled =
    _eventLoopScheduler
        .Schedule(() =>
        {
            /* Run code in the `EventLoopScheduler` */
        });

You can even schedule events in the future and make them recurring. To cancel scheduled code you can call scheduled.Dispose() .

Now, given private event EventHandler MyEvent; I can do this with the Rx libraries:

IDisposable subscription =
    Observable
        .FromEventPattern<EventHandler, EventArgs>(
            h => this.MyEvent += h,
            h => this.MyEvent -= h)
        .ObserveOn(_eventLoopScheduler)
        .Subscribe(x =>
        {
            /* Run code in the `EventLoopScheduler` */
        });

This subscribes to the event and pushes execution to the thread created by the EventLoopScheduler .

When you're done call subscription.Dispose() and _eventLoopScheduler.Dispose() to clean up and allow the thread to end.

Answer 2

As usual when I find an elegant solution to a problem I look at it and wonder why it didn't just pour out of my head that way? Sadly it took me a good while to get there but I'm happy with the result and how it could be made reusable with little effort.

I hope it's a useful and interesting read:

https://codinglifestyle.wordpress.com/2021/04/15/thread-synchronization-between-worker-threads/

Cheers, Chris