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Fix dotnet-watch Hot Reload deadlock on platforms with a startup SynchronizationContext #54131

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Fix dotnet-watch Hot Reload deadlock on platforms with a startup SynchronizationContext #54131

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9 changes: 7 additions & 2 deletions src/Dotnet.Watch/HotReloadAgent.Host/Listener.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -34,8 +34,13 @@ public Task Listen(CancellationToken cancellationToken)

try
{
// block execution of the app until initial updates are applied:
InitializeAsync(cancellationToken).GetAwaiter().GetResult();
// block execution of the app until initial updates are applied.
// Run on the thread pool (Task.Run) so that awaits inside InitializeAsync
// do not capture the calling thread's SynchronizationContext. Otherwise,
// on platforms where the startup-hook thread has a sync context (e.g. iOS,
// Android), the synchronous wait below would deadlock when an awaited
// continuation tries to resume on the same blocked thread.
Task.Run(() => InitializeAsync(cancellationToken), cancellationToken).GetAwaiter().GetResult();
Comment on lines +37 to +43
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Copilot AI Apr 28, 2026

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The deadlock fix is important, but it isn’t currently covered by a regression test. Since the repo already has unit tests that instantiate Listener (e.g., test/Microsoft.Extensions.DotNetDeltaApplier.Tests/HotReloadClientTests.cs), consider adding a test that runs Listener.Listen from a thread with a non-null SynchronizationContext and uses a test Transport.SendAsync that performs an await (e.g., Task.Yield) to validate that initialization completes (i.e., no sync-context deadlock) within a timeout.

Copilot generated this review using guidance from repository custom instructions.
}
catch (Exception e)
{
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