[release/11.0] Fix concurrent Unix named mutex creation - #134596
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## Why Concurrent shared compilations on Linux can intermittently fail when a newly created named mutex is initially owned. The creator can lose the mutex between publishing the shared state and recording ownership, causing a later `ReleaseMutex` to fail with "Cannot release a lock that is not owned by the current thread." ## What changed - Keep the creation/deletion process lock held through nonblocking initial mutex acquisition and ownership bookkeeping. - Preserve the existing behavior of releasing that lock before blocking waits. - Add a Unix regression test covering concurrent same-name constructors with initial ownership. ## Testing - `./build.sh clr+libs -rc checked` - `./build.sh clr.corelib+clr.nativecorelib+libs.pretest -rc checked` - `dotnet test src/libraries/System.Threading/tests/System.Threading.Tests.csproj --no-build` (714 passed) - Focused regression test passed. Resolves #134043 > [!NOTE] > This pull request description was generated with GitHub Copilot assistance. --------- Co-authored-by: Jeremy Koritzinsky <Jeremy.Koritzinsky@microsoft.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>
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Tagging subscribers to this area: @JulieLeeMSFT, @VSadov |
jkoritzinsky
approved these changes
Sep 24, 2026
This was referenced Sep 24, 2026
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/ba-g known issues. |
JulieLeeMSFT
approved these changes
Sep 25, 2026
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Backport of #134111 to release/11.0
/cc @jkoritzinsky
Customer Impact
Creating a new named mutex with the
initiallyOwnedparameter set totruefrom two threads in the same process could allow one of the threads to proceed without owning the mutex on Unix platforms.This was found by Roslyn in their move to use multithreaded MSBuild tasks.
Regression
#117635
Testing
Unit test added that forces this particular race many times in a loop until it occurs.
Risk
Low, only touches named mutex logic and the test validates the exact failure case reliably (always hits in the first 150 iterations on failure).