[RuntimeAsync] Enable runtime async in Libraries partition by VSadov · Pull Request #119432 · dotnet/runtime

VSadov · 2025-09-06T21:42:33Z

Mostly to see what happens and how far we can get with this.

VSadov · 2025-09-06T21:43:26Z

VSadov · 2025-09-06T21:59:02Z

A lot of tests actually run and pass when I run this locally. More than I expected. :-)

VSadov · 2025-09-06T21:59:07Z

Some JIT asserts:
(could be Roslyn NYIs, could be JIT issues)

 Assert failure(PID 49480 [0x0000c148], Thread: 48504 [0xbd78]): Assertion failed 'lastBlockILEndOffset < beginOffs' in 'System.Net.Tests.HttpListenerWebSocketTests:ReceiveAsync_ReadBuffer_WithWindowsAuthScheme_Success():this' during 'Generate code' (IL size 302; hash 0xef07e726; Tier0)
File: E:\dotnet004\runtime\src\coreclr\jit\scopeinfo.cpp:1566
Image: E:\dotnet004\runtime\artifacts\bin\testhost\net10.0-windows-Release-x64\dotnet.exe

 Assert failure(PID 62300 [0x0000f35c], Thread: 12816 [0x3210]): Assertion failed '!varTypeIsStruct(node) && !varTypeIsStruct(type)' in 'System.IO.Stream:ReadAsync(System.Memory`1[byte],System.Threading.CancellationToken):int:this' during 'Importation' (IL size 40; hash 0xaffe5a9c; FullOpts)
File: E:\dotnet004\runtime\src\coreclr\jit\gentree.h:4710
Image: E:\dotnet004\runtime\artifacts\bin\testhost\net10.0-windows-Release-x64\dotnet.exe

VSadov · 2025-09-06T22:03:47Z

Something odd is going on with sync context in a few cases:

System.Net.Http.Functional.Tests.PlatformHandler_HttpClientHandler_Asynchrony_Test.ResponseHeadersRead_SynchronizationContextNotUsedByHandler(responseHeadersRead: False, contentMode: BytePerChunk) [FAIL]
Sync Ctx used: at System.Environment.get_StackTrace() in E:\dotnet004\runtime\src\libraries\System.Private.CoreLib\src\System\Environment.cs:line 239
at System.Threading.Tests.TrackingSynchronizationContext.Post(SendOrPostCallback d, Object state)
at System.Threading.Tasks.AwaitTaskContinuation.RunCallback(ContextCallback callback, Object state, Task& currentTask) in E:\dotnet004\runtime\src\libraries\System.Private.CoreLib\src\System\Threading\Tasks\TaskContinuation.cs:line 697
at System.Threading.Tasks.Task.RunContinuations(Object continuationObject) in E:\dotnet004\runtime\src\libraries\System.Private.CoreLib\src\System\Threading\Tasks\Task.cs:line 3486
at System.Threading.Tasks.Task`1.TrySetResult(TResult result) in E:\dotnet004\runtime\src\libraries\System.Private.CoreLib\src\System\Threading\Tasks\Future.cs:line 385
at System.Threading.Tasks.TaskCompletionSource`1.TrySetResult(TResult result) in E:\dotnet004\runtime\src\libraries\System.Private.CoreLib\src\System\Threading\Tasks\TaskCompletionSource_T.cs:line 218
at System.Net.Http.WinHttpHandler.StartRequestAsync(WinHttpRequestState state) in E:\dotnet004\runtime\src\libraries\System.Net.Http.WinHttpHandler\src\System\Net\Http\WinHttpHandler.cs:line 1007
at System.Runtime.CompilerServices.AsyncHelpers.ThunkTaskCore.MoveNext[T,TOps](T task) in E:\dotnet004\runtime\src\coreclr\System.Private.CoreLib\src\System\Runtime\CompilerServices\AsyncHelpers.CoreCLR.cs:line 354
at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state) in E:\dotnet004\runtime\src\libraries\System.Private.CoreLib\src\System\Threading\ExecutionContext.cs:line 264
at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread) in E:\dotnet004\runtime\src\libraries\System.Private.CoreLib\src\System\Threading\Tasks\Task.cs:line 2346
at System.Threading.ThreadPoolWorkQueue.Dispatch() in E:\dotnet004\runtime\src\libraries\System.Private.CoreLib\src\System\Threading\ThreadPoolWorkQueue.cs:line 1154
at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart() in E:\dotnet004\runtime\src\libraries\System.Private.CoreLib\src\System\Threading\PortableThreadPool.WorkerThread.cs:line 118
at System.Threading.Thread.StartCallback() in E:\dotnet004\runtime\src\coreclr\System.Private.CoreLib\src\System\Threading\Thread.CoreCLR.cs:line 104

VSadov · 2025-09-09T21:17:17Z

I have a fix for the following assert:

 Assert failure(PID 7324 [0x00001c9c], Thread: 29684 [0x73f4]): Assertion failed 'callInfo.SaveAndRestoreSynchronizationContextField && (callInfo.SynchronizationContextLclNum != BAD_VAR_NUM)' in 'System.IO.Compression.Tests.ZipFile_Extract_Stream:ExtractToDirectoryRoundTrip(bool):this' during 'Transform async' (IL size 90; hash 0x550642b2; Tier0)
File: E:\dotnet004\runtime\src\coreclr\jit\async.cpp:1510
Image: E:\dotnet004\runtime\artifacts\bin\testhost\net10.0-windows-Release-x64\dotnet.exe

looking at others.

jakobbotsch · 2025-09-10T21:39:19Z

+ // TODO: (async) we do not need to save ByRef-containing locals
+ // as by the spec an await turns them into zero-inited state.
+ // For now just store/restore as if there are no gc refs.
+ // This is mostly to handle the "fake" live-across-await byrefs
+ // in min-opts, since C#-compiled code by itself does not let
+ // byrefs be live across awaits.
+ unsigned objCount = layout->HasGCByRef() ? 0 : layout->GetGCPtrCount();


We will need to figure out what is creating these LIR edges that are live across the await and stop doing that. This fix will replace assert with bad codegen instead.

I typically see the assert when compiling Debug code for Task-returning methods with ref-like parameters.
Ex:
publicstaticTaskWhenAll(paramsReadOnlySpan<Task>tasks){
async
This method is not async, but it's thunk will be async and will also have a byref-like parameter.
The part that the edge lives across the await is likely a result of Debug not tracking liveness precisely.
Once we have zeroing of byrefs that live across await, we may not need this.
This is not a fix. It is a workaround. - my goal is to get all Libraries tests pass or find something truly blocking.

Assuming that it is a result of Debug emit, perhaps forcing thunks to always compile optimized might be an alternative workaround, if there is an easy way to force.
I just thought of this workaround first and it seems working well enough.

The part that the edge lives across the await is likely a result of Debug not tracking liveness precisely.
There are two sources of live state across async calls in JIT IR:
Locals. These behave like IL locals and can be multiply defined and multiply used. They are what liveness analysis treat. They are added by AsyncLiveness::GetLiveLocals.
LIR edges. These are single-def single-use (SDSU) values that are defined in one place in a basic block and consumed later in the same basic block. When they overlap an async call (defined before, used after) they must also be preserved on heap. Liveness analysis does not treat these; they are known to be live when they overlap the call. They are added by AsyncTransformation::LiftLIREdges.
The liveness imprecision only comes into play for (1). However, we already ignore byref locals for these. It happens here:
runtime/src/coreclr/jit/async.cpp
Lines 507 to 515 in b0b30e7
if ((dsc->TypeIs(TYP_BYREF) && !dsc->IsImplicitByRef()) ||
(dsc->TypeIs(TYP_STRUCT) && dsc->GetLayout()->HasGCByRef()))
{
// Even if these are address exposed we expect them to be dead at
// suspension points. TODO: It would be good to somehow verify these
// aren't obviously live, if the JIT creates live ranges that span a
// suspension point then this makes it quite hard to diagnose that.
returnfalse;
}
That just leaves (2). But since these are known to be live, it is (almost?) always going to be a bug that resulted in these.

Good point! I will log an issue on this - to follow up with real fix.

VSadov · 2025-09-11T01:25:44Z

I see only 26 failed tests now in Chk/Ret configuration on win-x64.

There are 23 cases of Assertion failed 'lastBlockILEndOffset < beginOffs'
I will look at this next.

There are also 8 cases of Sync Ctx used: . . .
That could be harder to figure. I am not sure it is always deterministic.

Also fixing one thing sometimes exposes another, but so far with every fix/workaround I see more tests passing.

VSadov · 2025-09-17T04:18:35Z

The AVs in FinalizeTaskReturningThunk appear to be cased by a rare case where GS cookie check uses the same register as continuation.

Logged an issue on that - #119796 and pushed a possible fix here.

Now my local run is down to:

11 failures in -rc checked -lc debug config
15 failures in -rc checked -lc release config

MichalStrehovsky · 2025-12-11T13:27:50Z

Would it make sense to start testing with runtime async enabled in CoreLib too?

Copilot

Pull request overview

This PR attempts to enable the “runtime async” compiler feature for the Libraries build by setting MSBuild properties at the src/libraries level.

Changes:

Enable runtime-async=on via $(Features) under a runtime/arch/build-mode condition.
Globally suppress SYSLIB5007 warnings under src/libraries.
Enable preview features for all libraries builds.

Copilot · 2026-02-10T02:17:27Z

+ <PropertyGroup>
+ <Features Condition="'$(RuntimeFlavor)' != 'mono' and '$(TestBuildMode)' != 'nativeaot' and '$(TargetArchitecture)' != 'wasm'">$(Features);runtime-async=on</Features>
+ <NoWarn>$(NoWarn);SYSLIB5007</NoWarn>
+ <EnablePreviewFeatures>true</EnablePreviewFeatures>


EnablePreviewFeatures is being set unconditionally for all libraries builds (even when the runtime-async feature flag condition is false). That’s a very broad behavioral change; it should be conditioned the same way as runtime-async (or otherwise scoped to the intended partition) to avoid enabling preview language/features across the entire libraries build.

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…es do)

VSadov · 2026-02-17T21:50:38Z

This PR has lots of now outdated comments. I will open another one

VSadov added area-VM-coreclr runtime-async labels Sep 6, 2025

dotnet-policy-serviceBot added the linkable-framework Issues associated with delivering a linker friendly framework label Sep 6, 2025

dotnet-policy-serviceBot assigned VSadov Sep 6, 2025

VSadov added the NO-MERGE The PR is not ready for merge yet (see discussion for detailed reasons) label Sep 6, 2025

This was referenced Sep 10, 2025
Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. dotnet/dnceng#5922
Open
Sometimes the helix SDK uses GetWorkItemsAsync when workitems aren't done processing. dotnet/dnceng#6011
Open

jakobbotsch reviewed Sep 10, 2025
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VSadov force-pushed the asyncLibs branch from 1314892 to 6a29721Compare September 11, 2025 22:36

VSadov force-pushed the asyncLibs branch from 6a29721 to 518a7bfCompare September 16, 2025 01:43

VSadov mentioned this pull request Sep 17, 2025
[RuntimeAsync] Sometimes GS cookie check uses the same register as the continuation return. #119796
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build-analysisBot mentioned this pull request Sep 17, 2025
"We stopped hearing from agent Azure Pipelines 32. Verify the agent machine is running and has a healthy network connection" dotnet/dnceng#1886
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3 tasks

VSadov force-pushed the asyncLibs branch 2 times, most recently from 503a3d4 to 997d50eCompare December 16, 2025 03:25

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BinderTracingTest.ResolutionFlow times out #104670
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VSadov force-pushed the asyncLibs branch 2 times, most recently from e4bad2a to 4c67325Compare December 17, 2025 23:42

VSadov force-pushed the asyncLibs branch from 4c67325 to 5372c29Compare December 30, 2025 00:19

VSadov force-pushed the asyncLibs branch from 5372c29 to bce4596Compare January 6, 2026 22:52

build-analysisBot mentioned this pull request Jan 7, 2026
iOS.Device test WorkItemExecutions #122874
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VSadov force-pushed the asyncLibs branch from bce4596 to 7a12845Compare January 17, 2026 05:20

build-analysisBot mentioned this pull request Jan 17, 2026
browser-wasm linux LibraryTests build failure - NETSDK1022: Duplicate 'Content' items #123237
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VSadov force-pushed the asyncLibs branch from 7a12845 to 5263ec8Compare February 3, 2026 06:37

build-analysisBot mentioned this pull request Feb 3, 2026
XHarness package install failure on iOS due to devicectl NSPOSIXErrorDomain error 49 #123796
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VSadov mentioned this pull request Feb 3, 2026
Enable runtime-async feature switch for NativeAOT System.Private.CoreLib #123952
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CopilotAI review requested due to automatic review settings February 10, 2026 02:14

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System.IO.Tests.Directory_Create_Tests.FileSystemWatcher_Directory_Create_InNestedDirectory fails with "Created event did not occur as expected" #103630
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.NET Runtime-Async Feature #109632
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Comment threadsrc/libraries/Directory.Build.props
Comment threadsrc/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Finalization.cs

build-analysisBot mentioned this pull request Feb 14, 2026
MsQuic fails with QUIC_STATUS_OUT_OF_MEMORY on AzureLinux #123216
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Comment threadsrc/libraries/System.Threading.Channels/src/System/Threading/Channels/AsyncOperation.cs Outdated

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Comment threadsrc/libraries/Directory.Build.props

VSadov added 2 commits February 17, 2026 13:46

enable async in Libraries
c8c6011

NoWarn on SYSLIB5007 - in case we build against net10.0 (some utiliti…
e0f5ad7
…es do)

VSadov mentioned this pull request Feb 17, 2026
[RuntimeAsync] Enable runtime async in Libraries partition #124527
Closed

This was referenced Feb 17, 2026
Mono interpreter Segmentation fault crashes #124525
Closed
[android][clr] No peer certificates when executing System.Net.Http.Functional.Tests on Android emulator #124526
Closed

	if ((dsc->TypeIs(TYP_BYREF) && !dsc->IsImplicitByRef()) \|\|
	(dsc->TypeIs(TYP_STRUCT) && dsc->GetLayout()->HasGCByRef()))
	{
	// Even if these are address exposed we expect them to be dead at
	// suspension points. TODO: It would be good to somehow verify these
	// aren't obviously live, if the JIT creates live ranges that span a
	// suspension point then this makes it quite hard to diagnose that.
	returnfalse;
	}

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