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POComparing SynchronizationContext
 

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    <p>How do I compare SynchronizationContext? It seems that the same Dispatcher can create different SynchronizationContext when using BeginInvoke. When I drill down into the two (unequal) contexts, I see that the dispatcher Thread ID is the same, yet they are not Equal to each other.</p> <pre><code>public partial class MainWindow : Window { private SynchronizationContext contexta; private SynchronizationContext contextb; private SynchronizationContext contextc; private SynchronizationContext contextd; public MainWindow() { InitializeComponent(); contexta = SynchronizationContext.Current; Loaded += MainWindow_Loaded; } private void MainWindow_Loaded(object sender, RoutedEventArgs e) { contextb = SynchronizationContext.Current; Dispatcher.Invoke(() =&gt; { contextc = SynchronizationContext.Current; }); Dispatcher.BeginInvoke(new Action(() =&gt; { contextd = SynchronizationContext.Current; })); Debug.Assert(contexta != contextb); Debug.Assert(contexta == contextc); // fails... why?!?!? Debug.Assert(contexta == contextd); // fails... why?!?!? Debug.Assert(contextc == contextd); // fails... why?!?!? } </code></pre> <p>Maybe the two of them cannot be used together. I noticed that this actually works:</p> <pre><code> contexta.Send(new SendOrPostCallback((s) =&gt; { contexte = SynchronizationContext.Current; }), null); </code></pre> <p><strong>Update</strong> But strangely, it doesn't always work. </p> <pre><code> public override void AddRange(IEnumerable&lt;T&gt; items) { if (SynchronizationContext.Current == _context) { base.AddRange(items); } else { _context.Send(new SendOrPostCallback((state) =&gt; { AddRange(state as IEnumerable&lt;T&gt;); }), items); } } </code></pre> <p>never gets a matched _context and goes on forever, for example. Even though it shouldn't. This latter example the threads actually end up being the same, and there is a context, but it is different.</p> <p><strong>Update2</strong> Ok, I got it to work, but I really feel uncomfortable about it. Apparently, when you Post or Send, your task is run from the right thread, but if you aren't coming from the UI, it seems that a new SynchronizationContext is generated.</p> <pre><code> public override void AddRange(IEnumerable&lt;T&gt; items) { if (SynchronizationContext.Current == _context) { base.AddRange(items); } else { _context.Post(new SendOrPostCallback((state) =&gt; { if (SynchronizationContext.Current != _context) SynchronizationContext.SetSynchronizationContext(_context); // called every time.. strange AddRange(items); }), null); } } </code></pre> <p>And look at this:</p> <p><img src="https://i.stack.imgur.com/hWxBN.png" alt="enter image description here"></p> <p>"Requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code." :(</p>
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    1. COOnce you post from _context, it is actually executing in the correct thread. So it is conceivable that SetSync is not really needed.
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    2. COHas this just changed with .Net 4.5? I have an event aggregator that relied on getting the same synchronization context so that I could just invoke event actions that were already being published on the correct(subscriber) thread. It broke when I moved from 4 to 4.5.
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