fix(tidy3d): FXC-5400-fix-local-cache-race-conditions

[marcorudolphflex]

• Hardened local cache stats updates across processes:
  • Introduced a cross-process file lock with a clear lock boundary for entry-point operations.
  • Switched stats.json writes to unique temp files to avoid collisions.
  • Simplified locking so entry-points take the combined lock and helpers assume it’s held.

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Note

Medium Risk
Touches core caching I/O and locking behavior; while changes are localized, mistakes could deadlock or regress cache performance/consistency under concurrency.

Overview
Fixes local result cache corruption when multiple processes update the same cache directory.

LocalCache now wraps entry-point operations (list, clear, _fetch, _store, invalidate, sync_stats, etc.) in a combined in-process + inter-process filelock-based lock with a single, explicit lock boundary (helpers assume the lock is already held). stats.json (and other metadata) writes now use per-process unique temp filenames before os.replace, avoiding tmp-file collisions.

Adds multiprocessing regression tests that force concurrent _store / invalidate / stats updates, and updates dependencies (filelock added to core deps; lockfile changes in poetry.lock). CHANGELOG notes the local cache race fix.

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[github-actions]

Diff Coverage

Diff: origin/develop...HEAD, staged and unstaged changes

• tidy3d/web/cache.py (84.4%): Missing lines 201-203,205-206

Summary

• Total: 32 lines
• Missing: 5 lines
• Coverage: 84%

tidy3d/web/cache.py

Lines 197-210

  197     @contextmanager
  198     def _with_interprocess_lock(self) -> Iterator[None]:
  199         depth = getattr(self._file_lock_state, "depth", 0)
  200         if depth > 0:
! 201             self._file_lock_state.depth = depth + 1
! 202             try:
! 203                 yield
  204             finally:
! 205                 self._file_lock_state.depth -= 1
! 206             return
  207 
  208         self._lock_path.parent.mkdir(parents=True, exist_ok=True)
  209         self._root.mkdir(parents=True, exist_ok=True)
  210         with self._file_lock:

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[yaugenst-flex]

Nice!

[tylerflex]

Fixed the

ERROR: Failed to fetch cache results: [Errno 2] No such file or
                  directory: '/Users/twhughes/.cache/tidy3d/simulations/stats.tmp' ->
                  '/Users/twhughes/.cache/tidy3d/simulations/stats.json'

for me, thanks @marcorudolphflex !

btw I'm on Mac.

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