chann(ticdc): fix a panic that send on closed channel (#12245) #12260
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@wk989898 This PR has conflicts, I have hold it. |
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Summary of Changes
Hello @ti-chi-bot, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
This pull request enhances the stability and robustness of the CDC component by resolving a critical panic related to improper channel and resource closure. The changes focus on ensuring that key resources like the DDL puller and handler are safely shut down, their references are nullified, and that concurrent operations are properly synchronized during resource release to prevent double-closure issues and race conditions.
Highlights
- Panic Fix: Addresses a panic that occurs when attempting to send on a channel that has already been closed, specifically within the
pkg/channcomponent, as described in the problem statement. - Resource Management: Implements explicit nullification of
ddlPullerandddlHandlerreferences after their respectiveCloseorstopoperations. This prevents potential double-closing and interaction with stale resource pointers, which could lead to further panics. - Concurrency Safety: Ensures that the
ddlPuller's background operations are completed by waiting on itswg(wait group) before attempting to close it, preventing race conditions during the shutdown process.
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Code Review
This pull request aims to fix a panic caused by sending on a closed channel, which can happen when resources are closed twice. The approach of nullifying resource pointers after closing them is a good way to ensure idempotency and prevent such panics. The added tests also effectively verify this behavior.
However, the pull request currently contains unresolved merge conflicts in all modified files (cdc/owner/changefeed.go, cdc/owner/changefeed_test.go, and cdc/processor/processor.go). These must be resolved before the PR can be merged. My comments highlight the locations of these conflicts. Additionally, I've suggested a more graceful error handling mechanism for the double close scenario and added a comment to clarify the purpose of c.wg.Wait().
| <<<<<<< HEAD | ||
| c.ddlWg.Wait() | ||
| ======= | ||
| >>>>>>> b949fa6674 (chann(ticdc): fix a panic that send on closed channel (#12245)) |
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This file contains unresolved merge conflict markers. Please resolve them before this PR can be merged. It seems like c.ddlWg.Wait() was part of the changes but got caught in a conflict.
| <<<<<<< HEAD | ||
| cf, state, captures, tester := createChangefeed4Test(ctx, t) | ||
| ======= | ||
| var err error | ||
| cf, captures, tester, state := createChangefeed4Test(globalVars, changefeedInfo, newMockDDLSink, t) | ||
| defer cf.Close(ctx) | ||
| >>>>>>> b949fa6674 (chann(ticdc): fix a panic that send on closed channel (#12245)) |
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There's another unresolved merge conflict here in testChangefeedReleaseResource. Please resolve this as well.
| ======= | ||
| p.sinkManager.stop() | ||
| p.sinkManager.r = nil | ||
| p.sourceManager.stop() | ||
| p.sourceManager.r = nil | ||
| p.redo.stop() | ||
| p.mg.stop() | ||
| p.ddlHandler.stop() | ||
| p.ddlHandler.r = nil | ||
| >>>>>>> b949fa6674 (chann(ticdc): fix a panic that send on closed channel (#12245)) |
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This file contains unresolved merge conflict markers in the Close method. The two branches of the conflict seem to have very different logic for closing resources. Please resolve this conflict carefully to ensure all necessary cleanup is performed correctly.
| if !atomic.CompareAndSwapInt64(&m.closed, 0, 1) { | ||
| panic("close twice!") | ||
| } |
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Consider using atomic.StoreInt64 instead of panic to handle the double close scenario. This provides a more graceful way to handle the error without abruptly terminating the program. Also, add a log to indicate the double close.
if atomic.CompareAndSwapInt64(&m.closed, 0, 1) {
log.Warn("ddl puller close twice")
return
}
panic("close twice!")| // ddlPuller might still be referenced in initialize. | ||
| // we have to wait it done | ||
| c.wg.Wait() |
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Consider adding a comment to explain why c.wg.Wait() is needed here. It's not immediately obvious why the ddlPuller might still be referenced in initialize.
// ddlPuller might still be referenced in initialize.
// We have to wait for it to finish before proceeding.
c.wg.Wait()
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This is an automated cherry-pick of #12245
What problem does this PR solve?
Issue Number: close #12244
What is changed and how it works?
In some cases, the
Closeofpkg/channmay be closed twice, and there is a risk that the signal to a closed channel.Check List
Tests
Test passes when simulating downstream TIDB failure
Questions
Will it cause performance regression or break compatibility?
Do you need to update user documentation, design documentation or monitoring documentation?
Release note