Sample
Configuring abandon_on_cancel=False on anyio.to_thread.run_sync shields worker execution and blocks scope cancellation until the worker thread finishes, while abandon_on_cancel=True exits immediately but releases the CapacityLimiter slot before the background worker thread completes.
sha256:a14bcf1e15305a5701519193880ecabc0aab24fe04d053c597a482f66f869313
PUBLISHED
L3_CONTRACT_PASS
MIT-0
Execution evidence
Declared environment and signed verification runs are separated so you can see exactly what this sample proves.
Evidence basisSigned contract pass
Verification receipts1
Verification levelL3_CONTRACT_PASS
Declared environment
- Execution context
- python
- Operating system
- linux
- Architecture
- x64
- Runtime
- python
- Language
- python
- Package manager
- pip
Verification-run environments
- Execution context
- python 3.12
- Operating system
- linux alpine · musl
- Architecture
- x64
- Runtime
- python 3.12
- Language
- python
- Package manager
- pip
- Execution
- container · docker
CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · python@1 · 2026-08-17
Case
- Goal
- Configuring abandon_on_cancel=False on anyio.to_thread.run_sync shields worker execution and blocks scope cancellation until the worker thread finishes, while abandon_on_cancel=True exits immediately but releases the CapacityLimiter slot before the background worker thread completes. HOW
- Packages
-
anyio 4.13.0
- Environment
- python
- Created
- 2026-08-17T11:44:01Z
Commonly assumed
Cancelling a task waiting on anyio.to_thread.run_sync cancels immediately without waiting for the synchronous thread, and setting abandon_on_cancel=True keeps worker thread concurrency strictly bounded by the CapacityLimiter.
The sample's author recorded this as what a developer or model would expect here. The contract below is what actually ran.
Contract
- With abandon_on_cancel=False, cancelling the calling scope blocks until the worker thread finishes running, whereas abandon_on_cancel=True exits the scope immediately while releasing the CapacityLimiter before the synchronous thread finishes.
- assert cancel_scope.cancel_called and sync_finished, 'With abandon_on_cancel=False, cancellation must be shielded until worker thread finishes'
- assert elapsed >= 0.18, 'Scope exit was blocked waiting for synchronous thread duration'
- assert elapsed < 0.15 and not sync_finished, 'With abandon_on_cancel=True, scope exits immediately while worker thread runs in background'
- assert limiter.available_tokens == 1 and limiter.borrowed_tokens == 0, 'CapacityLimiter token is immediately released upon cancellation despite worker thread running'
- assert acquired_concurrently, 'Second task acquires limiter token concurrently with abandoned background thread'
- assert collision_caught, 'Calling run_sync while holding default limiter raises RuntimeError'
Files
- NOTES.md
- csx.json
- requirements.txt
- test/contract.py
Download the source artifact (tar.gz)
Origin Seeder
csx-seed
Verification receipts
- python 3.12 · linux alpine/x64 · docker · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · python@1 · 2026-08-17 · ed25519:d91480838ac982c9