Run FwDataFactory shutdown synchronously in StopAsync

[myieye]

Companion to sillsdev/libpalaso#1504, which catches the AbandonedMutexException itself. This PR removes a small but real abandonment-risk amplifier on the FwLite side: the unnecessary Task.Run inside FwDataFactory.StopAsync().

What

 public Task StopAsync(CancellationToken cancellationToken)
 {
     _shuttingDown = true;
-    return Task.Run(Dispose, cancellationToken);
+    Dispose();
+    return Task.CompletedTask;
 }

Why

• IHostedService.StopAsync is the host's contract to do shutdown work, and the host awaits the returned Task before terminating the process. Offloading Dispose() to a threadpool task gains nothing — StopAsync is not on a hot path.
• The previous form passed cancellationToken to Task.Run, which only cancels the scheduling of Dispose, not an in-flight Dispose. If StopAsync was called after the host's shutdown timeout had already elapsed (cancellationToken pre-signaled), the caches would never be disposed at all — the worst possible state for any file-locks or libpalaso GlobalMutex holds inside them.
• Running Dispose() synchronously on the StopAsync caller's thread keeps shutdown deterministic. Exceptions from Dispose() now propagate synchronously to the host instead of being captured in a Task that nobody awaits the result of.
• LcmCache.Dispose() (via WritingSystemManager.Save → libpalaso GlobalMutex.Lock) is sensitive to the threading model — System.Threading.Mutex has thread affinity. Reducing the number of thread hops on shutdown reduces the surface area where a process exit can race against an in-flight Dispose.

What this does NOT fix on its own

• The Task.Run(lcmCache.Dispose) in CloseProjectAsync is kept intentionally. That path is reachable from MAUI UI-thread callers (the "open in FieldWorks" handoff); removing the Task.Run there would freeze the UI during Dispose. The threadpool offload is correct in that location.
• The OnLcmProjectCacheEviction callback fires on the MemoryCache scanner thread and disposes the cache out from under whatever request is still using it. That's a use-after-dispose risk separate from mutex abandonment and needs a leasing/refcount scheme (the comment at lines 77–79 already flags it). Not in scope for this PR.

Risk

• Low. Behavior change is "wait synchronously" instead of "wait via Task.Run." Callers of StopAsync were already awaiting the returned Task; they now observe immediate completion after Dispose() returns. No public API change.
• The cancellationToken parameter is unused after this change — same as the existing StartAsync above it. Kept for IHostedService interface compatibility.

Tests

FwDataMiniLcmBridge.Tests runs 761/762 green (1 unrelated skip). No new test added: the change is a removal of a wrapper around an already-tested method.

🤖 Generated with Claude Code

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: d136e6f7-56da-4f57-8b9e-b55a706f4b7f

📥 Commits

Reviewing files that changed from the base of the PR and between 79a9816 and 7f09944.

📒 Files selected for processing (1)

• backend/FwLite/FwDataMiniLcmBridge/FwDataFactory.cs

---

📝 Walkthrough

Walkthrough

FwDataFactory.StopAsync is simplified to synchronously call Dispose() and return a completed task, eliminating asynchronous task scheduling during shutdown.

Changes

Synchronous disposal on shutdown

Layer / File(s)	Summary
Synchronous disposal in StopAsync backend/FwLite/FwDataMiniLcmBridge/FwDataFactory.cs	StopAsync marks shutdown as started, calls Dispose() directly, and returns Task.CompletedTask instead of queuing disposal via Task.Run(Dispose, cancellationToken).

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• sillsdev/languageforge-lexbox#2265: Adjusts shutdown and disposal behavior in the same FwDataFactory class to avoid race conditions during FieldWorks Lite close/open.
• sillsdev/languageforge-lexbox#2055: Changes disposal and shutdown behavior in FwDataFactory along related cache and project disposal paths.
• sillsdev/languageforge-lexbox#1992: Triggers graceful shutdown via app.StopAsync() which executes the modified disposal path.

Suggested reviewers

• hahn-kev
• imnasnainaec

Poem

🐰 A simpler path to rest,
No more queueing on the task stack—
Dispose now goes direct,
Shutdown's synchronous tack,
Cleaner paths, no race attack! 🎯

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/fwdata-factory-stopasync-sync

---

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[github-actions]

UI unit Tests

  1 files  ±0   59 suites  ±0   30s ⏱️ +3s
177 tests ±0  177 ✅ ±0  0 💤 ±0  0 ❌ ±0 
246 runs  ±0  246 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 7f09944. ± Comparison against base commit 79a9816.

[github-actions]

C# FwHeadless Unit Tests

48 tests  ±0   48 ✅ ±0   18s ⏱️ +3s
 5 suites ±0    0 💤 ±0 
 1 files   ±0    0 ❌ ±0 

Results for commit 7f09944. ± Comparison against base commit 79a9816.

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Build	Status	Details	Updated (UTC)
default (Inspect)	✅ No changes detected	-	Jun 2, 2026, 1:23 PM