Fix check for recursion in calls to AppContext.OnUnhandledException #119734
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The check is not correct and results in FailFast when a second thread tries to call this method. The `previousCrashingThreadId` is always the `s_crashingThreadId` for the second and following threads hitting this method. The correct check is to compare the `currentThreadId` with the `s_crashingThreadId`. Close dotnet#119731
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Pull Request Overview
This PR fixes a critical bug in the recursion detection logic for AppContext.OnUnhandledException that was causing incorrect FailFast crashes when multiple threads called the method concurrently.
Key Changes
- Corrected the recursion check by comparing currentThreadId against s_crashingThreadId instead of comparing s_crashingThreadId against previousCrashingThreadId
- This prevents false positive recursion detection when different threads call OnUnhandledException
jkotas
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Sep 15, 2025
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jkotas
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jkotas
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I am wondering whether it is worth it to write a regression test.
agocke
approved these changes
Sep 15, 2025
dfederm
approved these changes
Sep 15, 2025
This was referenced Sep 16, 2025
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AaronRobinsonMSFT
approved these changes
Sep 24, 2025
This was referenced Sep 24, 2025
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Deferring to #120069 |
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The check is not correct and results in FailFast when a second thread tries to call this method. The
previousCrashingThreadIdis always thes_crashingThreadIdfor the second and following threads hitting this method. The correct check is to compare thecurrentThreadIdwith thes_crashingThreadId.Close #119731