dispatcher: fix panic in conflict detector #1432
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Summary of Changes
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This pull request aims to fix a potential panic issue identified in the conflict detector component. The change implements a temporary measure by adding panic recovery around a specific channel send operation to prevent the program from crashing.
Highlights
- Panic Prevention: Added a
defer recover()block around the channel send operation within theOnNotifiedfunction of theConflictDetector. This is intended to catch potential panics that might occur if the notification channel is closed unexpectedly.
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Code Review
This pull request addresses a panic in the conflict detector caused by sending on a closed channel. The fix involves adding a defer statement with recover() within the node.OnNotified callback. This effectively catches the panic, logs a warning, and prevents the application from crashing, which is a good immediate solution. My review includes a suggestion for the TODO comment, outlining a more proactive pattern using context and select to potentially avoid the send attempt during shutdown, while still recommending keeping the recover as a failsafe.
| @@ -94,6 +94,12 @@ func (d *ConflictDetector) Add(event *commonEvent.DMLEvent) { | |||
| return d.nextCacheID.Add(1) % int64(len(d.resolvedTxnCaches)) | |||
| } | |||
| node. func()) { | |||
| // TODO:find a better way to handle the panic | |||
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The recover mechanism added here is a solid and pragmatic approach to prevent the panic from crashing the application, which is crucial for stability. It directly addresses the "send on closed channel" issue during concurrent operations, likely at shutdown.
Regarding the TODO: find a better way to handle the panic, a more proactive approach to avoid attempting the send on a potentially closed channel could involve using a select statement with a context that signals the ConflictDetector's lifecycle. For instance:
- Introduce a
context.Context(e.g.,ctxwith itscancelFunc) within theConflictDetectorstruct. This context would be initialized inNew()(possibly derived from a parent context passed in) and itscancelFunccalled at the beginning ofConflictDetector.Close(). - In this
OnNotifiedcallback, you could then use aselectstatement:// node. func()) { // // The defer/recover block (as currently implemented) should still be kept // // as a final safeguard due to potential subtle races. // defer func() { ... }() // // select { // case d.notifiedNodes.In() <- callback: // // Notification sent successfully // case <-d.ctx.Done(): // Check if the ConflictDetector is closing // log.Info("ConflictDetector is closing, notification not sent.", zap.String("reason", "context cancelled")) // } // }
This pattern attempts to gracefully bypass the send operation if the detector is shutting down, potentially reducing the number of logged warnings about failed sends. However, the defer recover (as you've implemented) remains essential as a robust final safety net, as race conditions in distributed systems or complex concurrent logic can sometimes still lead to unexpected states.
For the immediate goal of fixing the panic, your current solution is effective and appropriate.
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: asddongmen The full list of commands accepted by this bot can be found here. The pull request process is described here
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What problem does this PR solve?
Issue Number: close #1425
What is changed and how it works?
Check List
Tests
Questions
Will it cause performance regression or break compatibility?
Do you need to update user documentation, design documentation or monitoring documentation?
Release note