fix: release lock guards before awaiting channel send (#869)

[zmanian]

Summary

• cherry-pick the lock-guard release fix from fix: release lock guards before awaiting channel send (#869) #905 onto current staging
• carry over the regression-check workflow fix from fix: release lock guards before awaiting channel send (#869) #905
• include a CI-only skip marker commit because the regression gate is a known false negative on this change

Supersedes #905 for the staging merge train.

[gemini-code-assist]

Summary of Changes

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This pull request cherry-picks critical fixes from a previous PR (#905) to resolve a deadlock issue in asynchronous channel operations. The core problem involved RwLock guards being held across await points during message sending, which could block system shutdowns. The changes ensure that these locks are released promptly before asynchronous send operations, thereby preventing deadlocks and improving system stability. A new regression test has been added to verify this corrected behavior.

Highlights

• Deadlock Prevention: Addressed a deadlock scenario by ensuring RwLock guards are released before awaiting channel send operations across various channel implementations.
• Regression Testing: Introduced a new regression test in src/channels/http.rs to validate the fix for the deadlock during channel shutdown.
• Code Refactoring: Refactored message sending logic in wasm, web/handlers, web/server, and web/ws modules to prevent holding locks across await points.
• CI/Workflow Updates: Included a CI-only skip marker commit and carried over a regression-check workflow fix from a superseded pull request (fix: release lock guards before awaiting channel send (#869) #905).

Changelog

• src/channels/http.rs
  • Added a regression test to verify that channel shutdown completes even when process_message is blocked due to a full channel buffer, which previously caused a deadlock.
• src/channels/wasm/wrapper.rs
  • Modified WasmChannel::emit_messages to clone the message sender (tx) before iterating and sending messages, ensuring the RwLock read guard on message_tx is not held across send().await.
  • Refactored rate limiting logic in WasmChannel::emit_messages to acquire and release the rate_limiter write lock within a smaller scope, preventing it from being held across send().await.
  • Updated comments to clarify that no locks are held across send().await.
  • Applied similar changes to process_emitted_messages to clone the sender and scope the rate limiter lock.
• src/channels/web/handlers/chat.rs
  • Modified chat_send_handler and chat_approval_handler to clone the message sender (tx) after acquiring it from the msg_tx RwLock, ensuring the read guard is released before tx.send(msg).await.
• src/channels/web/server.rs
  • Modified chat_send_handler and chat_approval_handler to clone the message sender (tx) after acquiring it from the msg_tx RwLock, ensuring the read guard is released before tx.send(msg).await.
• src/channels/web/ws.rs
  • Modified handle_client_message in two locations to clone the message sender (tx) after acquiring it from the msg_tx RwLock, ensuring the read guard is released before tx.send(incoming).await.

Ignored Files

• Ignored by pattern: .github/workflows/** (1)
  • .github/workflows/regression-test-check.yml

Activity

• zmanian created this pull request to cherry-pick a lock-guard release fix from fix: release lock guards before awaiting channel send (#869) #905 onto the current staging branch.
• The PR also carries over a regression-check workflow fix from fix: release lock guards before awaiting channel send (#869) #905.
• A CI-only skip marker commit was included to address a known false negative on the regression gate.
• This pull request supersedes fix: release lock guards before awaiting channel send (#869) #905 for the staging merge train, indicating a focused effort to integrate these specific fixes.

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[zmanian]

Staging replacement for #905. This PR cherry-picks the actual lock-guard fix plus the regression-check workflow fix onto current staging, without carrying over the unrelated main merge history from the original branch.\n\nThe regression test gate on #905 was a false negative; this branch includes a CI-only [skip-regression-check] empty commit and the skip-regression-check label so the required check can pass while the rest of the matrix validates the real code changes.

[gemini-code-assist]

Code Review

This pull request correctly addresses a potential deadlock issue by ensuring RwLock read guards are not held across .await points. The fix is consistently applied across multiple channel implementations (http, wasm, web). Cloning the mpsc::Sender and scoping lock acquisitions are idiomatic and effective solutions in async Rust. The inclusion of a regression test in src/channels/http.rs is particularly commendable, as it specifically targets the deadlock scenario and ensures the fix is robust. The changes are clean, well-commented, and significantly improve the concurrency safety of the channel implementations.