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Prototyping T RuntimeHelpers.Await<T>(Task<T>) #2941

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Prototyping T RuntimeHelpers.Await<T>(Task<T>) #2941

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42ec5c2
T RuntimeHelpers.Await<T>(Task<T>)
VSadov Jan 16, 2025
76ca9da
state machine version of Await and friends
VSadov Jan 18, 2025
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11 changes: 9 additions & 2 deletions src/coreclr/jit/importercalls.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -528,7 +528,8 @@ var_types Compiler::impImportCall(OPCODE opcode,
// calls in JIT generated state machines only.
if (compIsAsync2() &&
((ni == NI_System_Runtime_CompilerServices_RuntimeHelpers_AwaitAwaiterFromRuntimeAsync) ||
(ni == NI_System_Runtime_CompilerServices_RuntimeHelpers_UnsafeAwaitAwaiterFromRuntimeAsync)))
(ni == NI_System_Runtime_CompilerServices_RuntimeHelpers_UnsafeAwaitAwaiterFromRuntimeAsync) ||
(ni == NI_System_Runtime_CompilerServices_RuntimeHelpers_Await)))
{
assert((call != nullptr) && call->OperIs(GT_CALL));
call->AsCall()->gtIsAsyncCall = true;
Expand Down Expand Up @@ -3376,7 +3377,8 @@ GenTree* Compiler::impIntrinsic(CORINFO_CLASS_HANDLE clsHnd,
}

if ((ni == NI_System_Runtime_CompilerServices_RuntimeHelpers_AwaitAwaiterFromRuntimeAsync) ||
(ni == NI_System_Runtime_CompilerServices_RuntimeHelpers_UnsafeAwaitAwaiterFromRuntimeAsync))
(ni == NI_System_Runtime_CompilerServices_RuntimeHelpers_UnsafeAwaitAwaiterFromRuntimeAsync) ||
(ni == NI_System_Runtime_CompilerServices_RuntimeHelpers_Await))
{
// These are marked intrinsics simply to mark the call node as async,
// which the caller will do. Make sure we keep pIntrinsicName assigned
Expand Down Expand Up @@ -10840,6 +10842,11 @@ NamedIntrinsic Compiler::lookupNamedIntrinsic(CORINFO_METHOD_HANDLE method)
result =
NI_System_Runtime_CompilerServices_RuntimeHelpers_UnsafeAwaitAwaiterFromRuntimeAsync;
}
else if (strcmp(methodName, "Await") == 0)
{
result =
NI_System_Runtime_CompilerServices_RuntimeHelpers_Await;
}
else if (strcmp(methodName, "SuspendAsync2") == 0)
{
result = NI_System_Runtime_CompilerServices_RuntimeHelpers_SuspendAsync2;
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1 change: 1 addition & 0 deletions src/coreclr/jit/namedintrinsiclist.h
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Expand Up @@ -120,6 +120,7 @@ enum NamedIntrinsic : unsigned short
NI_System_Runtime_CompilerServices_RuntimeHelpers_GetMethodTable,
NI_System_Runtime_CompilerServices_RuntimeHelpers_AwaitAwaiterFromRuntimeAsync,
NI_System_Runtime_CompilerServices_RuntimeHelpers_UnsafeAwaitAwaiterFromRuntimeAsync,
NI_System_Runtime_CompilerServices_RuntimeHelpers_Await,
NI_System_Runtime_CompilerServices_RuntimeHelpers_SuspendAsync2,
NI_System_Runtime_CompilerServices_RuntimeHelpers_get_RuntimeAsyncViaJitGeneratedStateMachines,

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6 changes: 6 additions & 0 deletions src/coreclr/nativeaot/System.Private.CoreLib/src/CompatibilitySuppressions.xml
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Expand Up @@ -857,6 +857,12 @@
<DiagnosticId>CP0002</DiagnosticId>
<Target>M:System.Threading.Lock.#ctor(System.Boolean)</Target>
</Suppression>
<Suppression>
<DiagnosticId>CP0002</DiagnosticId>
<Target>M:System.Runtime.CompilerServices.RuntimeHelpers.Await``1(System.Threading.Tasks.Task{``0})</Target>
<Left>ref/net10.0/System.Private.CoreLib.dll</Left>
<Right>lib/net10.0/System.Private.CoreLib.dll</Right>
</Suppression>
<Suppression>
<DiagnosticId>CP0002</DiagnosticId>
<Target>M:System.Runtime.CompilerServices.RuntimeHelpers.AwaitAwaiterFromRuntimeAsync``1(``0)</Target>
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1 change: 1 addition & 0 deletions src/coreclr/vm/corelib.h
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Expand Up @@ -685,6 +685,7 @@ DEFINE_METHOD(RUNTIME_HELPERS, FINALIZE_VALUETASK_RETURNING_THUNK, Finalize
DEFINE_METHOD(RUNTIME_HELPERS, FINALIZE_VALUETASK_RETURNING_THUNK_1, FinalizeValueTaskReturningThunk, GM_Continuation_RetValueTaskOfT)
DEFINE_METHOD(RUNTIME_HELPERS, UNSAFE_AWAIT_AWAITER_FROM_RUNTIME_ASYNC_1, UnsafeAwaitAwaiterFromRuntimeAsync, GM_T_RetVoid)
DEFINE_METHOD(RUNTIME_HELPERS, AWAIT_AWAITER_FROM_RUNTIME_ASYNC_1, AwaitAwaiterFromRuntimeAsync, GM_T_RetVoid)
DEFINE_METHOD(RUNTIME_HELPERS, AWAIT_1, Await, GM_TaskOfT_RetT)

DEFINE_CLASS(SPAN_HELPERS, System, SpanHelpers)
DEFINE_METHOD(SPAN_HELPERS, MEMSET, Fill, SM_RefByte_Byte_UIntPtr_RetVoid)
Expand Down
1 change: 1 addition & 0 deletions src/coreclr/vm/metasig.h
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Expand Up @@ -571,6 +571,7 @@ DEFINE_METASIG_T(IM(RetValueTask, _, g(VALUETASK)))

DEFINE_METASIG_T(GM(Exception_RetTaskOfT, IMAGE_CEE_CS_CALLCONV_DEFAULT, 1, C(EXCEPTION), GI(C(TASK_1), 1, M(0))))
DEFINE_METASIG_T(GM(T_RetTaskOfT, IMAGE_CEE_CS_CALLCONV_DEFAULT, 1, M(0), GI(C(TASK_1), 1, M(0))))
DEFINE_METASIG_T(GM(TaskOfT_RetT, IMAGE_CEE_CS_CALLCONV_DEFAULT, 1, GI(C(TASK_1), 1, M(0)), M(0)))
DEFINE_METASIG_T(GM(Exception_RetValueTaskOfT, IMAGE_CEE_CS_CALLCONV_DEFAULT, 1, C(EXCEPTION), GI(g(VALUETASK_1), 1, M(0))))
DEFINE_METASIG_T(GM(T_RetValueTaskOfT, IMAGE_CEE_CS_CALLCONV_DEFAULT, 1, M(0), GI(g(VALUETASK_1), 1, M(0))))

Expand Down
4 changes: 3 additions & 1 deletion src/coreclr/vm/threadsuspend.cpp
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Expand Up @@ -4915,7 +4915,9 @@ bool IsSpecialCaseAsyncRet(MethodDesc* pMD)
// causing loading to happen? Also, can we just mark them as async2 in SPC,
// or force them to be fully interruptible?
LPCUTF8 name = pMD->GetName();
return strcmp(name, "UnsafeAwaitAwaiterFromRuntimeAsync") == 0 || strcmp(name, "AwaitAwaiterFromRuntimeAsync") == 0;
return strcmp(name, "UnsafeAwaitAwaiterFromRuntimeAsync") == 0 ||
strcmp(name, "AwaitAwaiterFromRuntimeAsync") == 0 ||
strcmp(name, "Await") == 0;
}

static bool GetReturnAddressHijackInfo(EECodeInfo *pCodeInfo, ReturnKind *pReturnKind, bool* hasAsyncRet)
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69 changes: 69 additions & 0 deletions src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.cs
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Expand Up @@ -208,6 +208,75 @@ public static void UnsafeAwaitAwaiterFromRuntimeAsync<TAwaiter>(TAwaiter awaiter
SuspendAsync2(sentinelContinuation);
return;
}

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@VSadov VSadov Jan 17, 2025 •
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The interesting part. The rest of code changes are mechanical - to make the helper known as special method.

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I don't see a good reason to not write this function in terms of UnsafeAwaitAwaiterFromRuntimeAsync. This looks more complicated than necessary.

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I don't see a good reason to not write this function in terms of UnsafeAwaitAwaiterFromRuntimeAsync. This looks more complicated than necessary.

Possibly. I started on that path, but was running into asserts (something about conditional BB not ending with conditional jump,...).

I was not sure if that was something that I did wrong or issues with SuspendAsync2 in unusual context.

This way worked though.

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I don't think we will need an explicit SuspendAsync2 once we switch to use UnsafeAwaitAwaiter... with everything hooked up. The JIT should create the state machine itself at that point.

// TODO: should this be called "AwaitFromRuntimeAsync" ? (i.e. same as above, but no "Awaiter")
//
// Marked intrinsic since this needs to be
// recognizes as an async2 call.
[Intrinsic]
[BypassReadyToRun]
[MethodImpl(MethodImplOptions.NoInlining)]
public static unsafe T Await<T>(Task<T> task)
{
// TODO: handle complete tasks more efficiently.
//if (!task.IsCompleted)
//{
ref RuntimeAsyncAwaitState state = ref t_runtimeAsyncAwaitState;
Continuation? sentinelContinuation = state.SentinelContinuation;
if (sentinelContinuation == null)
state.SentinelContinuation = sentinelContinuation = new Continuation();

Continuation myContinuation = new Continuation();
myContinuation.GCData = new object[] { task };
myContinuation.Resume = &AwaitHelper<T>.Resume;

state.Notifier = task.GetAwaiter();
sentinelContinuation.Next = myContinuation;

// RETURN {default(T), myContinuation}
//
SuspendAsync2(myContinuation);

// unreachable
return task.ResultOnSuccess;
//}
//else
//{
// // RETURN {task.Result, null}
// //
// T result = task.Result;
// ReturnAsync2(Unsafe.AsPointer(ref result));
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Just guessing how ReturnAsync2 could look.

If generic intrisic is ok, it could also be just ReturnAsync2<T>(result)

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I don't think we need an intrinsic, this can just be a normal return.

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Would a regular return guarantee that the continuation return is null?

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It would need the VM to tell the JIT this function has runtime-async calling convention. That's probably something we'd want anyway. It might also be the only thing we need to allow using UnsafeAwaitAwaiterFromRuntimeAsync in its implementation.

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I will try. We do not do that for UnsafeAwaitAwaiterFromRuntimeAsync, but that may work just because it is a simpler method.

//
// // unreachable
// return result;
//}
}

internal static class AwaitHelper<T>
{
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Resuming the continuation simply pushes the result into the caller continuation. (or throws, if faulted)

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I wonder if UnsafeAwaitAwaiterFromRuntimeAsync needs to call GetResult() upon resuming as well? (in case it faulted)

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Also GetAwaiter().GetResult() seems more appropriate than .Result. This is just a rough prototype anyways.

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@jakobbotsch jakobbotsch Jan 17, 2025 •
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I wonder if UnsafeAwaitAwaiterFromRuntimeAsync needs to call GetResult() upon resuming as well? (in case it faulted)

The caller is responsible for calling awaiter.GetResult() (UnsafeAwaitAwaiterFromRuntimeAsync has no way to bind to the awaiter anyway).

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The caller is responsible for calling awaiter.GetResult()

Ah, right, in this case we have code in the caller.

public static Continuation? Resume(Continuation continuation)
{
Task<T> task = (Task<T>)continuation.GCData![0]!;
Continuation next = continuation.Next!;

if (IsReferenceOrContainsReferences<T>())
{
next.GCData![0] = task.Result;
}
else
{
int retIndex =
(next.Flags & CorInfoContinuationFlags.CORINFO_CONTINUATION_OSR_IL_OFFSET_IN_DATA) != 0 ?
4 :
0;

// TODO: WriteUnaligned?
Unsafe.As<byte, T>(ref next.Data![retIndex]) = task.Result;
}

return null;
}
}
#endif
}
}
1 change: 1 addition & 0 deletions src/libraries/System.Runtime/ref/System.Runtime.cs
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Expand Up @@ -13708,6 +13708,7 @@ public static void RunModuleConstructor(System.ModuleHandle module) { }
public delegate void TryCode(object? userData);
public static void UnsafeAwaitAwaiterFromRuntimeAsync<TAwaiter>(TAwaiter awaiter) where TAwaiter : ICriticalNotifyCompletion { }
public static void AwaitAwaiterFromRuntimeAsync<TAwaiter>(TAwaiter awaiter) where TAwaiter : INotifyCompletion { }
public static T Await<T>(System.Threading.Tasks.Task<T> task) { throw null; }
}
public sealed partial class RuntimeWrappedException : System.Exception
{
Expand Down
9 changes: 9 additions & 0 deletions src/tests/async/varying-yields-await.csproj
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@@ -0,0 +1,9 @@
<Project Sdk="Microsoft.NET.Sdk.IL">
<PropertyGroup>
<Optimize>True</Optimize>
<DefineConstants>AWAIT;$(DefineConstants)</DefineConstants>
</PropertyGroup>
<ItemGroup>
<Compile Include="varying-yields.cs" />
</ItemGroup>
</Project>
21 changes: 19 additions & 2 deletions src/tests/async/varying-yields.cs
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Expand Up @@ -4,6 +4,8 @@
//#define ASYNC1_TASK
//#define ASYNC1_VALUETASK

#pragma warning disable 4014, 1998

using System;
using System.Collections.Generic;
using System.Diagnostics;
Expand Down Expand Up @@ -91,9 +93,19 @@ async2 Task<long>
double liveState3 = _yieldProbability;

if (depth == 0)
#if AWAIT
return RuntimeHelpers.Await(Loop());
#else
return await Loop();
#endif

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Using Await in a benchmark/test.

long result =
#if AWAIT
RuntimeHelpers.Await(Run(depth - 1));
#else
await Run(depth - 1);
#endif

long result = await Run(depth - 1);
Sink = (int)liveState1 + (int)liveState2 + (int)(1 / liveState3) + depth;
return result;
}
Expand All @@ -117,7 +129,12 @@ async2 Task<long>
{
for (int i = 0; i < 20; i++)
{
numIters += await DoYields();
numIters +=
#if AWAIT
RuntimeHelpers.Await(DoYields());
#else
await DoYields();
#endif
}
}

Expand Down