AF: The continuation was the completion sentinel.

[jkotas]

The continuation was the completion sentinel.
   at System.Threading.Channels.AsyncOperation.SignalCompletion() in /_/src/libraries/System.Threading.Channels/src/System/Threading/Channels/AsyncOperation.cs:line 212
   at System.Threading.Channels.AsyncOperation.TrySetException(Exception exception) in /_/src/libraries/System.Threading.Channels/src/System/Threading/Channels/AsyncOperation.cs:line 152
   at System.Threading.Channels.ChannelUtilities.FailOperations[TAsyncOp](TAsyncOp head, Exception error) in /_/src/libraries/System.Threading.Channels/src/System/Threading/Channels/ChannelUtilities.cs:line 308
   at System.Threading.Channels.RendezvousChannel`1.RendezvousChannelWriter.TryComplete(Exception error) in /_/src/libraries/System.Threading.Channels/src/System/Threading/Channels/RendezvousChannel.cs:line 295

Build Information

Build: https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_build/results?buildId=1389277
Build error leg or test failing: System.Diagnostics.Process.Tests.WorkItemExecution
Pull request: #127206

Error Message

Fill the error message using step by step known issues guidance.

{
  "ErrorMessage": "The continuation was the completion sentinel.",
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1389277
Error message validated: [The continuation was the completion sentinel.]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 4/21/2026 6:17:39 PM UTC

Report

Build	Definition	Test	Pull Request
1389277	dotnet/runtime	System.Diagnostics.Process.Tests.WorkItemExecution	#127206

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
0	1	1

[jkotas]

cc @jakobbotsch @VSadov

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[VSadov]

It is likely just one more ordering issue with a reusable ValueTask source. Similar to #126373

I will take a look.

AsyncOperation and ManualResetValueTaskSource implement a delicate pattern where producers and consumers of events communicate through a shared state that can be pooled/reused. They were known before to have races that show up only on ARM.

I do not think this is related to runtime async.

[VSadov]

Complete stack:
(does not look like anything is using runtime async, just ordinary flow from a Socket event to a handler)

The assert complains about completing an event source that has been already completed.
Possibly the write that cleared the state after the previous use has been delayed.

The continuation was the completion sentinel.
   at System.Threading.Channels.AsyncOperation.SignalCompletion() in /_/src/libraries/System.Threading.Channels/src/System/Threading/Channels/AsyncOperation.cs:line 212
   at System.Threading.Channels.AsyncOperation.TrySetException(Exception exception) in /_/src/libraries/System.Threading.Channels/src/System/Threading/Channels/AsyncOperation.cs:line 152
   at System.Threading.Channels.ChannelUtilities.FailOperations[TAsyncOp](TAsyncOp head, Exception error) in /_/src/libraries/System.Threading.Channels/src/System/Threading/Channels/ChannelUtilities.cs:line 308
   at System.Threading.Channels.RendezvousChannel`1.RendezvousChannelWriter.TryComplete(Exception error) in /_/src/libraries/System.Threading.Channels/src/System/Threading/Channels/RendezvousChannel.cs:line 295
   at System.Diagnostics.Process.<>c__DisplayClass210_0.<ReadAllLinesAsync>g__ReadToChannelAsync|0(StreamReader reader, Boolean standardError, CancellationToken ct) in /_/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Multiplexing.cs:line 331
   at System.Threading.Tasks.Task.RunContinuations(Object continuationObject) in /_/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:line 3658
   at System.Threading.Tasks.Task.RunContinuations(Object continuationObject) in /_/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:line 3658
   at System.Threading.Tasks.Sources.ManualResetValueTaskSourceCore`1.SetResult(TResult result) in /_/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Sources/ManualResetValueTaskSourceCore.cs:line 68
   at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.OnCompleted(SocketAsyncEventArgs _) in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Tasks.cs:line 1017
   at System.Net.Sockets.SocketAsyncEventArgs.OnCompletedInternal() in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.cs:line 214
   at System.Net.Sockets.SocketAsyncEventArgs.FinishOperationAsyncSuccess(Int32 bytesTransferred, SocketFlags flags) in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.cs:line 1130
   at System.Net.Sockets.SocketAsyncEventArgs.CompletionCallback(Int32 bytesTransferred, SocketFlags flags, SocketError socketError) in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.Unix.cs:line 389
   at System.Net.Sockets.SocketAsyncEventArgs.TransferCompletionCallbackCore(Int32 bytesTransferred, Memory`1 socketAddress, SocketFlags receivedFlags, SocketError socketError) in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.Unix.cs:line 108
   at System.Net.Sockets.SocketAsyncContext.BufferMemoryReceiveOperation.InvokeCallback(Boolean allowPooling) in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncContext.Unix.cs:line 501
   at System.Net.Sockets.SocketAsyncContext.OperationQueue`1.ProcessAsyncOperation(TOperation op) in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncContext.Unix.cs:line 1027
   at System.Net.Sockets.SocketAsyncContext.ProcessAsyncReadOperation(ReadOperation op) in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncContext.Unix.cs:line 1466
   at System.Net.Sockets.SocketAsyncContext.ReadOperation.System.Threading.IThreadPoolWorkItem.Execute() in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncContext.Unix.cs:line 340
   at System.Net.Sockets.SocketAsyncContext.AsyncOperation.Process() in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncContext.Unix.cs:line 291
   at System.Net.Sockets.SocketAsyncContext.HandleEvents(SocketEvents events) in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncContext.Unix.cs:line 2297
   at System.Net.Sockets.SocketAsyncEngine.System.Threading.IThreadPoolWorkItem.Execute() in /_/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEngine.Unix.cs:line 279
   at System.Threading.ThreadPoolWorkQueue.Dispatch() in /_/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolWorkQueue.cs:line 950
   at System.Threading.PortableThreadPool.WorkerThread.WorkerDoWork(PortableThreadPool threadPoolInstance) in /_/src/libraries/System.Private.CoreLib/src/System/Threading/PortableThreadPool.WorkerThread.cs:line 145
   at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart() in /_/src/libraries/System.Private.CoreLib/src/System/Threading/PortableThreadPool.WorkerThread.cs:line 121
   at System.Threading.Thread.StartCallback(Thread* pThread) in /_/src/coreclr/System.Private.CoreLib/src/System/Threading/Thread.CoreCLR.cs:line 119

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