C# Thread in Thread: how to get SynchronizationContext.Current ?

Question

I have a WindowsForms application wich has SynchronizationContext.Current not null
But from that WindowsForms app I create a new Thread called thread1
From thread1 I create another Thread called thread2
When I try to POST methods from thread2 in thread1 using SynchronizationContext.Current, will fail because SynchronizationContext.Current is null

Please give me a solution to POST a method from thread2 to thread1, but asynchronously

Answer 1

Because thread1 is in the synchronisation context that will handle the posted message, you need to post using thread1's synchronization context. (Think of the synchronization context as the message receiver.) So you need to pass thread1's synchronization context to thread2 somehow. One way is to pass it as a parameter to thread2 using a ParameterisedThreadStart delegate:

private void Thread2Func(object obj)
{
  SynchronizationContext parentThread = (SynchronizationContext)obj;
  // ...
  parentThread.Post(someCallback, someState);
}

and in thread1:

thread2 = new Thread(Thread2Func);
thread2.Start(SynchronizationContext.Current);