fix(session): add file locking to prevent race conditions in multi-session sync#52
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JasonOA888 wants to merge 1 commit intoHKUDS:mainfrom
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fix(session): add file locking to prevent race conditions in multi-session sync#52JasonOA888 wants to merge 1 commit intoHKUDS:mainfrom
JasonOA888 wants to merge 1 commit intoHKUDS:mainfrom
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…ssion sync Fixes HKUDS#51 ## Root Cause _auto_save() writes to session file without any locking mechanism. When multiple CLI commands run concurrently (e.g., 'layer add' + 'text edit'), they can: 1. Both read the same state 2. Both write their changes 3. Result: lost updates (one write overwrites the other) ## Solution Add fcntl file locking (LOCK_EX) during save: - Exclusive lock during write - Atomic updates prevent lost data - Fallback for systems without flock support ## Testing - [x] Concurrent CLI commands no longer drop state - [x] Works on Linux/macOS (fcntl available) - [x] Graceful fallback on unsupported filesystems ## Impact Multi-session workflows now have consistent state sync.
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great bug-finding. Can we improve HARNESS.md slightly to prevent this? |
JasonOA888
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Mar 13, 2026
Following PR HKUDS#52, add a new subsection to 'Critical Lessons Learned' documenting best practices for session file locking: - Use fcntl.flock() for exclusive locking during writes - Prevent race conditions in multi-session scenarios - Handle filesystems that don't support flock - Document common pitfalls (use fcntl.flock, not flock directly) This prevents future contributors from making similar mistakes when implementing session persistence. Co-authored-by: yuh-yang <yuh-yang@users.noreply.github.com>
sanjayrohith
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Mar 14, 2026
Fixes HKUDS#51. When multiple CLI commands run concurrently against the same project file, concurrent writes to session/project JSON could silently overwrite each other due to missing file locking. Adds exclusive fcntl.flock() locking inside every save method across all 10 harnesses that write JSON state to disk: - gimp, blender, inkscape, audacity, libreoffice, obs-studio, kdenlive: save_session() in core/session.py - shotcut, drawio: save_session_state() in core/session.py - anygen: save() in core/session.py A try/except (ImportError, OSError) fallback ensures the write still proceeds on Windows (no fcntl) or unsupported filesystems. The lock is explicitly released after the write completes. PR HKUDS#52 addressed this for anygen only; this commit extends the same protection to all remaining harnesses. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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ZJZAC
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Mar 17, 2026
…ll harnesses Closes HKUDS#51 The root cause: all 10 harnesses used bare `open("w") + json.dump()` for session saves. `open("w")` truncates the file before any lock can be acquired, so concurrent writes silently corrupt or lose data. Fix: add `_locked_save_json()` to each session.py that opens with "r+" (no truncation), acquires fcntl.LOCK_EX, then truncates inside the lock. Falls back gracefully on Windows where fcntl is unavailable. Also: - Update HARNESS.md with session file locking guidance (per maintainer request on PR HKUDS#52) - Add concurrent write tests (4 threads × 50 writes) to verify the fix Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Fixes #51
Root Cause
_auto_save()writes to session file without any locking mechanism. When multiple CLI commands run concurrently, they can both read the same state, then both write their changes, resulting in lost updates.Solution
Add fcntl file locking (LOCK_EX) during save:
Changes
Testing
Impact
Multi-session workflows now have consistent state sync.