Sample
Configure joblib parallel execution with parallel_config and verify backend constraint resolution, nested context propagation, and failure modes on contradictory settings.
sha256:358ff91d26968481475e6fb33480225b3c25f6adba6d6bb2170118ee39c4a2de
Publication state. LOCAL_PASS passed only on its author's machine; PUBLISHED is public and awaiting independent verification; CROSS_PASS was reproduced by another verifier; MATRIX_PASS passed across environment boundaries; STABLE has sustained independent passes without recent failures.
Evidence strength. L0 is source only; L1 resolved dependencies; L2 compiled or loaded; L3 passed its contract; L4 was independently reproduced; L5 passed across different environments.
MIT-0
Execution evidence
Declared environment and signed verification runs are separated so you can see exactly what this sample proves.
- Evidence basis
- Independent cross-verification
- Verification receipts
- 2
- Verification level
- L4_CROSS_PASS
Declared environment
python linux x64 python python pip
Verification-run environments
| Environment | Contract | Stages | Run |
|---|---|---|---|
| python 3.12 · linux alpine/x64 · docker ed25519:d91480838ac982c9 | PASS | compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS CONTAINER_RUN · python@1 |
2026-08-19 |
| python 3.12 · linux alpine/x64 · docker ed25519:2175b912ea1c23b1 | PASS | compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS CONTAINER_RUN · python@1 |
2026-08-19 |
Case
HOW- Goal
- Configure joblib parallel execution with parallel_config and verify backend constraint resolution, nested context propagation, and failure modes on contradictory settings.
- Packages
- Symbols
-
- joblib.parallel_config
- joblib.Parallel
- joblib.delayed
- joblib.parallel.get_active_backend
- Environment
- python
- Created
- 2026-08-19T13:42:06Z
Contract
- Setting prefer='threads' in parallel_config with n_jobs=4 switches to ThreadingBackend but silently resets implicit n_jobs in context to 1, while explicit backend='threading' preserves n_jobs=4.
- Explicitly passing n_jobs=4 to Parallel overrides the thread fallback reset back to 4.
- Setting require='sharedmem' without an explicit backend forces ThreadingBackend and resets implicit n_jobs to 1.
- Contradictory settings prefer='processes' and require='sharedmem' raise ValueError on Parallel instantiation.
- Instantiating Parallel(backend='multiprocessing', require='sharedmem') raises ValueError, whereas configuring the same settings under parallel_config silently downgrades to ThreadingBackend and resets n_jobs to 1.
- Nested parallel_config scopes override configuration parameters within their block and restore outer context settings upon exit.
- Passing backend constructor parameters such as inner_max_num_threads without an explicit backend raises ValueError at context entry.
- Passing an unregistered backend name to parallel_config raises ValueError immediately at context entry.
Files
- NOTES.md
- csx.json
- requirements.txt
- test/contract.py