7795: fs: simplify lock handling

[martin-augment]

7795: To review by AI

[coderabbitai]

Walkthrough

A refactor in the file synchronization methods modifies how locking is performed. The sync_all and sync_data methods in tokio/src/fs/file.rs were updated to chain the lock acquisition with the complete_inflight call, replacing the previous pattern of storing the lock in a local variable. The behavioral outcome remains identical, with no changes to control flow or error handling apart from reducing the scope of lock acquisition. No public API signatures were modified.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch pr-7795-2025-12-29-11-30-13

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📜 Recent review details

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Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between a68edc4 and 68e60c7.

📒 Files selected for processing (1)

• tokio/src/fs/file.rs

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (2)

• GitHub Check: Cursor Bugbot
• GitHub Check: claude-review

🔇 Additional comments (2)

tokio/src/fs/file.rs (2)

312-317: LGTM! Lock scope correctly narrowed.

The chained lock().await.complete_inflight().await releases the mutex immediately after completing in-flight operations, before cloning std and calling asyncify. Since those operations don't require the lock, this reduces contention as intended.

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346-351: LGTM! Consistent lock handling improvement.

Same beneficial change as sync_all: the lock is released immediately after ensuring in-flight operations complete, reducing unnecessary contention during the blocking sync_data call.

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[claude]

Code Review: PR #41 - fs: simplify lock handling

Summary

This PR simplifies lock handling in sync_all() and sync_data() by chaining method calls instead of storing the lock guard in an intermediate variable.

Code Quality ✅

Positive aspects:

• The refactoring is clean and improves code conciseness
• Reduces intermediate variables, making the code more streamlined
• Consistent with the pattern used in try_clone() at line 463

Style:

• The chained call pattern self.inner.lock().await.complete_inflight().await is already used elsewhere in the codebase, so this change improves consistency

Correctness Analysis ✅

Lock lifetime behavior:
The change is semantically correct but worth understanding:

Before:

let mut inner = self.inner.lock().await;
inner.complete_inflight().await;

The lock guard inner is held from acquisition until the end of the function scope (or until dropped).

After:

self.inner.lock().await.complete_inflight().await;

The lock guard is an unnamed temporary that lives until the end of the statement containing complete_inflight().await.

Why this is safe:
The lock is only needed during complete_inflight(). After that completes, both versions release the lock before calling asyncify(). The difference is that the new version releases the lock slightly earlier (end of statement vs. end of function), which is actually preferable as it reduces lock contention.

Potential Issues ⚠️

Inconsistency with set_len():
Notice that set_len() at line 384 still uses the old pattern:

let mut inner = self.inner.lock().await;
inner.complete_inflight().await;
// ... continues to use inner

This is intentional because set_len() needs to access inner.state after completing in-flight operations. However, consider documenting why some functions need the lock guard stored vs. chained.

Performance Considerations ✅

Improvement:

• Slightly better performance due to earlier lock release
• Reduced time window where the mutex is held
• No allocation or runtime overhead changes

Security Concerns ✅

No security implications identified. The change doesn't affect:

• Thread safety (mutex semantics preserved)
• Memory safety (guard lifetime is valid)
• Error handling paths

Test Coverage ⚠️

Observation:
The PR doesn't include new tests, but this is acceptable because:

• This is a pure refactoring with no behavioral changes
• Existing tests should cover the functionality
• The pattern is already used elsewhere in the codebase

Recommendation:
Consider running the existing test suite to verify no regressions:

cargo test --package tokio --lib fs::file

Additional Observations

1. Mutability marker removed: The mut keyword was removed from the binding since the guard is no longer explicitly used. This is correct since complete_inflight() takes &mut self, and the method receiver provides the necessary mutability.

2. Consistency opportunity: The same pattern could potentially be applied to other similar locations if they don't need the guard afterward.

Recommendation: ✅ APPROVE

This is a solid cleanup PR that:

• Improves code consistency
• Reduces unnecessary variable bindings
• Maintains correctness
• Slightly improves performance through earlier lock release

The changes are minimal, focused, and follow existing patterns in the codebase.

[augmentcode]

🤖 Augment PR Summary

Summary: Simplifies tokio::fs::File::sync_all and sync_data by inlining the mutex guard when calling complete_inflight().

Why: Reduces boilerplate/lock-handling verbosity while still flushing any in-flight buffered operations before delegating to the underlying std::fs::File sync calls.

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[augmentcode]

Review completed. No suggestions at this time.

Comment augment review to trigger a new review at any time.

[cursor]

Lock released early causes race condition in sync methods

The refactoring from let mut inner = self.inner.lock().await; inner.complete_inflight().await; to self.inner.lock().await.complete_inflight().await; changes when the mutex lock is released. In the original code, the MutexGuard was stored in inner and held until the function returned, including during the asyncify(...) call. In the new code, the guard is a temporary that drops immediately after complete_inflight().await returns, releasing the lock before std.sync_all() executes. This allows concurrent writes to start between complete_inflight() finishing and the actual sync occurring, potentially leaving data unsynced despite sync_all() returning successfully.

Additional Locations (1)

• tokio/src/fs/file.rs#L346-L347

 

[martin-augment]

value:delightful; category:bug; feedback:The Bugbot AI reviewer is correct! Currently the mutex lock is held for the whole method body lifetime and thus protect parallel executions to lead to racing issues. The proposed changes in this PR should not be accepted. In addition the try_clone() method should be improved to behave the same way.

[martin-augment]

Correctness Analysis ✅

Lock lifetime behavior: The change is semantically correct but worth understanding:

Before:

let mut inner = self.inner.lock().await;
inner.complete_inflight().await;

The lock guard inner is held from acquisition until the end of the function scope (or until dropped).

After:

self.inner.lock().await.complete_inflight().await;

The lock guard is an unnamed temporary that lives until the end of the statement containing complete_inflight().await.

Why this is safe: The lock is only needed during complete_inflight(). After that completes, both versions release the lock before calling asyncify(). The difference is that the new version releases the lock slightly earlier (end of statement vs. end of function), which is actually preferable as it reduces lock contention.

value:annoying; category:bug; feedback:The Claude AI reviewer is not correct! Currently the mutex lock is held for the whole method body lifetime and thus protect parallel executions to lead to racing issues. The proposed changes in this PR should not be accepted. In addition the try_clone() method should be improved to behave the same way.

[martin-augment]

🤖 Augment PR Summary

Summary: Simplifies tokio::fs::File::sync_all and sync_data by inlining the mutex guard when calling complete_inflight(). Why: Reduces boilerplate/lock-handling verbosity while still flushing any in-flight buffered operations before delegating to the underlying std::fs::File sync calls.

value:annoying; category:bug; feedback:The Augment AI reviewer is not correct! Currently the mutex lock is held for the whole method body lifetime and thus protect parallel executions to lead to racing issues. The proposed changes in this PR should not be accepted. In addition the try_clone() method should be improved to behave the same way.