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Fix AsyncInstrumentation to honor s_asyncDebuggingEnabled #127233

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Fix AsyncInstrumentation to honor s_asyncDebuggingEnabled #127233

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9 changes: 9 additions & 0 deletions ...raries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncInstrumentation.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,15 @@ private static Flags InitializeFlags()
{
if (IsUninitialized(s_activeFlags))
{
// The debugger may have set Task.s_asyncDebuggingEnabled directly via ICorDebug
// before any ETW session is established. In that case, s_asyncDebuggerActiveFlags
// will still be Disabled because OnEventCommand was never called. Honor the
// debugger's request by enabling default flags when s_asyncDebuggingEnabled is set.
if (s_asyncDebuggerActiveFlags == Flags.Disabled && Task.s_asyncDebuggingEnabled)
{
s_asyncDebuggerActiveFlags = DefaultFlags | Flags.AsyncDebugger;
}
Comment on lines +110 to +117
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Copilot AI Apr 21, 2026

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This new fallback behavior (enabling AsyncInstrumentation when only Task.s_asyncDebuggingEnabled is set, without an ETW session) doesn’t appear to be covered by existing runtime-async tests. Consider adding a test that sets Task.s_asyncDebuggingEnabled via reflection without creating a TplEventSource listener, then triggers flag initialization (e.g., via a RuntimeAsyncMethodGeneration async method) and asserts AsyncInstrumentation.s_activeFlags becomes enabled (and that the relevant runtime-async collections are initialized as expected).

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Comment on lines +114 to +117
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Copilot AI Apr 21, 2026

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With this change, if Task.s_asyncDebuggingEnabled is later cleared (e.g., debugger detach) in a non-ETW scenario where OnEventCommand never calls UpdateAsyncDebuggerFlags(Disabled), s_asyncDebuggerActiveFlags/s_activeFlags will remain non-Disabled and keep routing RuntimeAsyncTask through the instrumented path (even though AsyncDebugger hooks will be gated by Task.s_asyncDebuggingEnabled). If detach/toggling is expected to work without ETW, consider adding a corresponding “disable” path (e.g., re-check Task.s_asyncDebuggingEnabled in SyncActiveFlags/InstrumentCheckPoint or another explicit update mechanism).

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s_activeFlags = s_asyncProfilerActiveFlags | s_asyncDebuggerActiveFlags;
}

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