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fix(state): reload before change_state so a stale snapshot can't revert a sibling State's write - #4694
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…rt a sibling State's write Under shared_state, molecule builds one State object per Config sharing the same state.yml. change_state wrote back its whole in-memory _data on every call, so a State object constructed before another one's write still had the old values in memory and clobbered them on its next change_state call. change_state now reloads _data from disk before applying its key, so it always merges onto the latest persisted state instead of its own snapshot. reset() is untouched; it intentionally overwrites the whole file. Fixes ansible#4689 Signed-off-by: Amir Fathi <amirfathi.me@gmail.com>
📝 WalkthroughWalkthrough
ChangesShared state write preservation
Estimated code review effort: 2 (Simple) | ~10 minutes Suggested reviewers: Merge Risk: 🟡 Moderate · up to This change preserves sequential updates from sibling State instances, but concurrent workers can still lose state changes when writes overlap. Shared-state parallel use remains unsafe until the full update transaction is serialized. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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Inline comments:
In `@src/molecule/state.py`:
- Line 210: Serialize the full state update transaction around self._get_data(),
the assignment, and _write_state_file so concurrent workers cannot overwrite
each other with stale snapshots. Update the relevant `@marshal` flow and use a
process- or file-level lock held across all three operations; locking only the
read or write is insufficient.
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src/molecule/state.pytests/unit/test_state.py
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No need, thanks. It's already noted as out of scope in the PR body, and I'll open an issue myself if the cross-process locking work happens. |
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I reviewed this because I filed #4666, which covers the same read-modify-write mechanism from the parallel side, and I wrote the I verified the test is a genuine red/green rather than a test that passes either way. Reverting only the two production lines in With the change restored, 14/14 pass. A few notes, none of them blocking. The deferred lock has an issue already. You flagged in the description that two concurrent writers under Reads still serve the stale snapshot. The properties (
Two things I checked and found clean, in case they come up:
Leaving |
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Bumping this: jeffcpullen independently verified the fix and both follow-up notes are addressed in the description now. Let me know if there's anything else you want changed before this gets a look. |
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@AmirF194 the CI is red. Can you please have a look? |
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Same two legs as before this PR (tox/lint, tox/check): prek's cspell dictionary hook trims words like "failover" as unused and fails the job on the resulting git-dirty status. It's not our diff, those words aren't in state.py or the test, and main's own tox/lint run with identical dictionary content is green. Looks like a PR-context vs push-context divergence in the cspell hook itself. |
Code Review: PR #4694 - Reload before change_statePR: #4694 Executive SummaryVerdict: READY_FOR_HUMAN_REVIEW ✅ This PR is technically sound and should be merged. It correctly fixes the sequential race condition described in issue #4689, where multiple State objects holding stale snapshots of the same state.yml file would clobber each other's writes. The implementation is minimal, well-tested, and the trade-offs are clearly understood and documented. Overall Assessment:
Detailed Findings1. FUNCTIONALITY ANALYSIS ✅What the PR DoesThe fix is surgically targeted: in # Added 2 lines to state.py change_state method:
if key not in VALID_KEYS:
raise InvalidState
+ # Reload first so a sibling State object's write under shared_state isn't reverted.
+ self._data = self._get_data()
self._data[key] = valueDoes It Solve #4689?Yes, definitively. ✅ Root Cause (from issue):
How PR fixes it:
Verification from PR comments:
Edge Cases & Correctness ✅1. Why not reload in
2. Race window still exists for concurrent writers (acknowledged):
3. No reload on reads (properties):
4.
Test Coverage ✅Added test: def test_change_state_does_not_clobber_a_sibling_states_write(
_instance: state.State,
config_instance: config.Config,
) -> None:
# _instance constructed first (stale snapshot of state.yml)
creator = state.State(config_instance)
creator.change_state("created", True) # writes created=True to disk
# _instance still has old snapshot (created=False) in memory
_instance.change_state("prepared", True) # should NOT revert created
on_disk = util.safe_load_file(_instance.state_file)
assert on_disk["created"] is True # ✅ Verifies fix
assert on_disk["prepared"] is True # ✅ Verifies fixVerification: Test is genuine red/green (confirmed by reverting production code). Assessment: Test directly validates the fix; correctly simulates the scenario in the bug report. ✅ 2. SECURITY ANALYSIS ✅Potential Security ImplicationsQ: Does reloading from disk introduce security vulnerabilities? A: No. ✅ The security posture is unchanged or improved:
Note: The PR uses Threat Model Assessment
Conclusion: No new security concerns. ✅ 3. QUALITY ANALYSISCode QualityStrengths:
Weaknesses:
Code Quality Score: 8/10 Test QualityStrengths:
Weaknesses:
Test Quality Score: 8/10 DocumentationDocstring Coverage Warning: CodeRabbit flagged 20% coverage vs. 80% required Analysis:
Recommendation: Document any internal functions if maintainers require, but this is not a blocker. The PR author acknowledged this is out of scope (comment: "It's already noted as out of scope in the PR body"). Documentation Quality Score: 6/10 Known Limitations (Acknowledged in PR)
Verdict: All limitations are appropriately documented and deferred. They do not block this PR. Review of PR DiscussionPositive Feedback ✅
CI Status
|
| Risk | Likelihood | Impact | Mitigation |
|---|---|---|---|
| Regression in non-shared-state mode | Low | High | ✅ PR adds reload on every change_state() call, not just shared_state; behavior is strictly more correct |
| Performance regression | Low | Medium | ✅ One extra file read per change_state() call; state.yml is small; acceptable cost |
| New concurrency bug | Medium | Medium | ✅ Acknowledged; does not claim to fix true concurrency; tracked in #4666 |
| Stale reads through properties | Medium | Low | ✅ Deferred to #4666; pre-existing in default mode too |
Overall Risk: LOW 🟢
Questions for Maintainers
- Is the deferred scope acceptable? ✅ (PR author and reviewers agree yes)
- Should docstring coverage be addressed before merge? (Optional; recommend if standard requires it)
- Is the cspell CI issue known? (Appears unrelated; please verify before merge)
Conclusion
Verdict: ✅ READY_FOR_HUMAN_REVIEW
This PR should be merged. It is:
- Correct: Fixes the stated problem (Molecule 26.6.0: stale
SharedStateobject overwritescreatedduringprepare#4689) with no regressions - Well-tested: Genuine red/green test verifying the fix
- Well-scoped: Defers acknowledged concurrent-write issues to Shared state gets corrupted when running scenarios in parallel, flaking CI #4666
- Well-documented: Clear description and PR comments address design trade-offs
- Low-risk: Changes only the reload behavior; cannot make things worse
Scores by Lens
| Lens | Score | Evidence |
|---|---|---|
| Functionality | 8/10 | Correctly solves #4689; acknowledged limitations are appropriate for scope |
| Security | 9/10 | No new vulnerabilities; already reading/writing the same file |
| Quality | 6/10 | Good code and tests; docstring coverage warning is pre-existing/optional |
Final Recommendation
✅ APPROVE AND MERGE with optional docstring improvements.
Appendix: Implementation Details
Changed Files
src/molecule/state.py (2 lines added)
- Added reload of
self._databefore key assignment inchange_state() - Line 209: Inline comment explaining the change
- Line 210:
self._data = self._get_data()
tests/unit/test_state.py (17 lines added)
- New test:
test_change_state_does_not_clobber_a_sibling_states_write - Simulates the scenario: two State objects, one built before the other writes
- Verifies both keys persist in the final state.yml
Decorator Flow
change_state("prepared", True)
↓
@marshal decorator:
- Call change_state() method
- Inside method: reload self._data, set self._data[key] = value
- After method returns: call self._write_state_file()
↓
Result: Latest state.yml is read, mutated locally, written back atomically
Consistency with #4667 (atomic_write_file PR)
This PR complements #4667 (atomic write of state file):
- fix: write the scenario state file atomically #4667: Ensures the write to state.yml is atomic (no torn reads)
- fix(state): reload before change_state so a stale snapshot can't revert a sibling State's write #4694: Ensures the write reflects the latest state (no clobbering from stale snapshot)
Both are necessary for correctness; together they improve state consistency significantly.
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Thanks for merging, and for double checking the cspell CI legs weren't from this diff. Will open a follow up under #4666 if the concurrent-writer locking work happens. |
Fixes #4689.
Confirmed the root cause you found:
change_statemutates its own_datadict andmarshalwrites that whole dict back, so aStateobject constructed before create runs still hascreated: falsein memory and stomps it back onto disk whenpreparecallschange_state("prepared", True)later.Went with option 2 from the issue:
change_statenow reloads_datafrom disk right before applying the key it's changing, so it always merges onto whatever the last writer actually persisted instead of its own possibly-stale snapshot. Leftreset()alone since it's meant to blow away the whole file (used bydestroy), not merge.One thing I didn't add: a lock around the reload-then-write. This closes the sequential-construction race in your repro (default_config's State and the scenario's State disagreeing because one was built before the other's write), but two genuinely concurrent writers under
--workerscould still interleave between the reload and the write.atomic_write_fileguarantees no reader sees a torn file, not that two writers can't race. That's tracked as defect 2 in #4666, so no new issue needed for it.Added a unit test that builds two
Stateobjects against the same state file the wayshared_statedoes: the first setscreated, then the second (still holding the older snapshot) setsprepared. On main the second write revertscreatedback to false; with the change both keys stick.Summary by CodeRabbit
Bug Fixes
Tests