Managed fixes for async task tracking #123727

rcj1 · 2026-01-28T19:24:11Z

No description provided.

dotnet-policy-service · 2026-01-28T21:01:15Z

Tagging subscribers to this area: @steveisok, @tommcdon, @dotnet/dotnet-diag
See info in area-owners.md if you want to be subscribed.

Copilot

Pull request overview

This PR adds managed fixes for async task tracking by introducing tick count tracking for runtime async tasks and continuations to support debugging scenarios.

Changes:

Adds two new ConcurrentDictionary fields to track task and continuation tick counts for debugging
Implements methods to set, get, update, and remove tick count tracking for both tasks and continuations
Integrates tick count tracking into the continuation allocation and dispatch flow
Adds TPL event source tracing for synchronous work begin/end and operation begin/end events

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

File	Description
src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs	Adds static dictionaries and helper methods for tracking task and continuation tick counts, removes unnecessary blank line
src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs	Integrates tick count tracking into continuation lifecycle, adds ContinuationEqualityComparer, extends AsyncDispatcherInfo with Task field, adds TPL event source tracing

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

Copilot · 2026-01-29T18:47:41Z

src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs

+        {
+            if (s_asyncDebuggingEnabled)
+            {
+                s_runtimeAsyncContinuationTicks ??= new Collections.Concurrent.ConcurrentDictionary<Continuation, long>(ContinuationEqualityComparer.Instance);


Inconsistent namespace qualification: The ConcurrentDictionary type should be fully qualified as System.Collections.Concurrent.ConcurrentDictionary to match the field declarations on lines 184 and 187. The file does not have a using System.Collections.Concurrent; directive.

Copilot · 2026-01-29T18:47:41Z

src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs

+        {
+            if (s_asyncDebuggingEnabled)
+            {
+                s_runtimeAsyncContinuationTicks ??= new Collections.Concurrent.ConcurrentDictionary<Continuation, long>(ContinuationEqualityComparer.Instance);


Inconsistent namespace qualification: The ConcurrentDictionary type should be fully qualified as System.Collections.Concurrent.ConcurrentDictionary to match the field declarations on lines 184 and 187. The file does not have a using System.Collections.Concurrent; directive.

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

noahfalk · 2026-01-30T07:15:18Z

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

        }
    }

+    internal class ContinuationEqualityComparer : IEqualityComparer<Continuation>


What difference does it make specifying this comparer? Is this a workaround for missing functionality in the Continuation class where most objects have this default behavior but Continuations are special?

Yes, the virtual functions do not work on Continuations.

It can use a comment

noahfalk · 2026-01-30T07:16:07Z

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

+#else
+        [FieldOffset(8)]
+#endif
+        public Task Task;


A comment describing which Task gets stored here and when would be helpful.

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

noahfalk · 2026-01-30T07:32:56Z

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs


                        ref byte resultLoc = ref nextContinuation != null ? ref nextContinuation.GetResultStorageOrNull() : ref GetResultStorage();
+                        long tickCount = Task.GetRuntimeAsyncContinuationTicks(curContinuation, out long tickCountVal) ? tickCountVal : Environment.TickCount64;
+                        Task.UpdateRuntimeAsyncTaskTicks(this, tickCount);


I would have guessed the tick count represented the first time a Task starts doing work but this seems to be updating the tick count every time a new continuation starts. Is that the desired behavior? It would be helpful to have a nice comment somewhere that describes what behavior we are trying to achieve with these side data structures.

I have added some comments on the methods and around them

noahfalk · 2026-01-30T07:36:27Z

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

+                        Task.UpdateRuntimeAsyncTaskTicks(this, tickCount);
                        Continuation? newContinuation = curContinuation.ResumeInfo->Resume(curContinuation, ref resultLoc);

+                        Task.RemoveRuntimeAsyncContinuationTicks(curContinuation);


If the continuation executes quickly is there a risk its already deleted before the debugger ever gets an opportunity to observe it? Would that matter or the debugger only cares about observing the tasks which are in-progress at the moment a debug event occurs?

I should add comments to all of this code. The UpdateRuntimeAsyncTaskTicks Is just to keep track of the start time of the invocation currently inflight, as it is not on the chain. Once its work is done we remove it.

noahfalk · 2026-01-30T07:47:47Z

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

            Continuation newContinuation = (Continuation)RuntimeTypeHandle.InternalAllocNoChecks(contMT);
 #endif
            prevContinuation.Next = newContinuation;
+            Task.SetRuntimeAsyncContinuationTicks(newContinuation, Environment.TickCount64);


we also mentioned swapping from TickCount to StopWatch if the debugger cares about getting higher precision timings.

This is good because the etw events are also QPC timed

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs

Added comments to clarify the purpose of the Task field.

e

7d950cb

github-actions bot added the needs-area-label An area label is needed to ensure this gets routed to the appropriate area owners label Jan 28, 2026

dotnet-policy-service bot assigned rcj1 Jan 28, 2026

jkotas added runtime-async area-Diagnostics-coreclr and removed needs-area-label An area label is needed to ensure this gets routed to the appropriate area owners labels Jan 28, 2026

This was referenced Jan 29, 2026

The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

Open

[android-arm64] The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#6408

Open

TBD: remove unneeded updates

788fb65

Copilot AI review requested due to automatic review settings January 29, 2026 18:37

Copilot started reviewing on behalf of rcj1 January 29, 2026 18:38 View session

Copilot AI reviewed Jan 29, 2026

View reviewed changes

This was referenced Jan 30, 2026

"We stopped hearing from agent Azure Pipelines 32. Verify the agent machine is running and has a healthy network connection" dotnet/dnceng#1886

Open

iOS.Device test WorkItemExecutions #122874

Open

noahfalk reviewed Jan 30, 2026

View reviewed changes

adding IDs etc

908059e

build-analysis bot mentioned this pull request Jan 30, 2026

[android][arm64] System.Net.Sockets.Tests.SendTo_SyncForceNonBlocking.Datagram_UDP_ShouldImplicitlyBindLocalEndpoint fails with NetworkUnreachable #120526

Open

comments and restructure etc

6bc980b

Copilot AI review requested due to automatic review settings January 31, 2026 20:57

Copilot started reviewing on behalf of rcj1 January 31, 2026 20:58 View session

Copilot AI reviewed Jan 31, 2026

View reviewed changes

Enhance comments for Task field in AsyncHelpers

79ced18

Added comments to clarify the purpose of the Task field.

rcj1 force-pushed the managed-fixes branch from df57a44 to 79ced18 Compare January 31, 2026 23:50

This was referenced Feb 1, 2026

XHarness package install failure on iOS due to devicectl NSPOSIXErrorDomain error 49 #123796

Open

System.Transactions.Tests.OleTxTests.Recovery timeout #122621

Open

Managed fixes for async task tracking #123727

Are you sure you want to change the base?

Managed fixes for async task tracking #123727

Conversation

rcj1 commented Jan 28, 2026

Uh oh!

dotnet-policy-service bot commented Jan 28, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

Copilot AI Jan 29, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 29, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants