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Merged
filmor merged 1 commit into from
Sep 29, 2026
+17 −3
Merged

Document MONO_THREADS_SUSPEND and use throughout CI #2747

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6 changes: 3 additions & 3 deletions .github/workflows/main.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,8 @@ jobs:

env:
NUGET_PACKAGES: ${{ github.workspace }}/.nuget/packages
# Apply to every Mono host, including pytest and the .NET Python test runner.
MONO_THREADS_SUSPEND: preemptive # https://github.com/mono/mono/issues/21466
steps:
- name: Checkout code
uses: actions/checkout@v7
Expand Down Expand Up @@ -84,8 +86,6 @@ jobs:
- name: Embedding tests (Mono/.NET Framework)
if: always()
run: dotnet test --runtime any-${{ matrix.os.platform }} --framework net472 --logger "console;verbosity=detailed" src/embed_tests/
env:
MONO_THREADS_SUSPEND: preemptive # https://github.com/mono/mono/issues/21466

- name: Embedding tests (.NET Core)
if: always()
Expand All @@ -97,7 +97,7 @@ jobs:

- name: Python Tests (Mono)
if: always()
run: pytest --runtime mono
run: uv run pytest --runtime mono -v -o faulthandler_timeout=60

- name: Python Tests (.NET Framework)
if: ${{ matrix.os.category == 'windows' }}
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14 changes: 14 additions & 0 deletions doc/source/threading.rst
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Expand Up @@ -93,6 +93,20 @@ Forgetting this is the most common pythonnet threading bug. Symptoms range
from immediate segfaults to subtle refcount corruption that crashes much
later.

Mono thread suspension
----------------------

On Linux and macOS, Mono's cooperative/hybrid thread suspension can hang
when Python and managed threads interact. If affected, set
``MONO_THREADS_SUSPEND=preemptive`` before starting the process, as described
in `mono/mono#21466 <https://github.com/mono/mono/issues/21466>`_.
CI uses this workaround for both embedding and Python-hosted tests.

To run the Mono Python tests with per-test output and a Python thread
stack dump if a test takes longer than 60 seconds::

MONO_THREADS_SUSPEND=preemptive uv run pytest --runtime mono -v -o faulthandler_timeout=60

Reference counting and finalizers
---------------------------------

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