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Posted to github@beam.apache.org by "shunping (via GitHub)" <gi...@apache.org> on 2025/09/21 04:00:17 UTC
[PR] Fix a deadlock situation for BlockOnSplit test case. [beam]
shunping opened a new pull request, #36226:
URL: https://github.com/apache/beam/pull/36226
A deadlock can occur in the `TestDynamicSplit/BlockOnSplit` test case due to a race condition between two go routines, the `processPlan` and `splitPlan` goroutines:
- `processPlan` - This is the routine where `ProcessElement`, `GetRestriction` and `TryClaim` are called. https://github.com/apache/beam/blob/65dfd30684d38d27e86dc77b7d056119ee0447a9/sdks/go/pkg/beam/core/runtime/exec/dynsplit_test.go#L442
- `splitPlan` - This is the routine where `TrySplit` is called.
The splitBlockingDriver uses channels for synchronization.
https://github.com/apache/beam/blob/65dfd30684d38d27e86dc77b7d056119ee0447a9/sdks/go/pkg/beam/core/runtime/exec/dynsplit_test.go#L178-L182
However, a specific execution order can lead to a deadlock:
- Driver executes and starts `processPlan` and `splitPlan`.
- Driver waits for a signal on the `sdf.proc` channel from `ProcessElement` in `processPlan` routine
- `TrySplit` in `splitPlan` routine executes first, acquires the `rt.mu` lock and then blocks while waiting on the `rt.blocksplit` channel.
https://github.com/apache/beam/blob/65dfd30684d38d27e86dc77b7d056119ee0447a9/sdks/go/pkg/beam/core/runtime/exec/dynsplit_test.go#L399-L401
- `ProcessElement` in `processPlan` routine executes `GetRestriction` where it tries to acquire `rt.mu` but it is already-held.
https://github.com/apache/beam/blob/65dfd30684d38d27e86dc77b7d056119ee0447a9/sdks/go/pkg/beam/core/runtime/exec/dynsplit_test.go#L422
- Unfortunately, `ProcessElement` can only send the signal to the `sdf.proc` channel after `GetRestriction` is finished.
https://github.com/apache/beam/blob/65dfd30684d38d27e86dc77b7d056119ee0447a9/sdks/go/pkg/beam/core/runtime/exec/dynsplit_test.go#L443-L444
This creates a circular dependency and a deadlock. This change resolves the issue by moving the signal on `rt.blockSplit` to before the mutex is locked, preventing the deadlock.
fixes #36224
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Re: [PR] Fix a deadlock situation for BlockOnSplit test case. [beam]
Posted by "gemini-code-assist[bot] (via GitHub)" <gi...@apache.org>.
gemini-code-assist[bot] commented on PR #36226:
URL: https://github.com/apache/beam/pull/36226#issuecomment-3315481241
## Summary of Changes
Hello @shunping, I'm Gemini Code Assist[^1]! 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 resolves a critical deadlock scenario identified in the `TestDynamicSplit/BlockOnSplit` test case. The deadlock stemmed from a specific timing issue where two goroutines, `processPlan` and `splitPlan`, contended for a shared mutex while waiting on each other's signals. By carefully reordering the mutex acquisition and channel signaling within the `splitTestRTracker`'s `TryClaim` and `TrySplit` methods, this change eliminates the circular dependency, ensuring the test case can execute reliably without encountering the previously observed deadlock.
### Highlights
* **Deadlock Resolution**: Addresses a deadlock in the `TestDynamicSplit/BlockOnSplit` test case caused by a race condition between `processPlan` and `splitPlan` goroutines. The issue arose when `TrySplit` acquired a mutex and blocked, while `ProcessElement` simultaneously attempted to acquire the same mutex, leading to a circular dependency.
* **Synchronization Logic Adjustment**: The fix involves reordering operations within the `splitTestRTracker`'s `TryClaim` and `TrySplit` methods. Specifically, the `rt.blockSplit` signal is now sent *before* acquiring the `rt.mu` mutex, which effectively breaks the circular dependency and prevents the deadlock.
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Re: [PR] Fix a deadlock situation for BlockOnSplit test case. [beam]
Posted by "shunping (via GitHub)" <gi...@apache.org>.
shunping commented on PR #36226:
URL: https://github.com/apache/beam/pull/36226#issuecomment-3322237667
FYI, I ran the test 1000x with race detector and could not see a stuck test.
```
go test -v -race -count=1000 github.com/apache/beam/sdks/v2/go/pkg/beam/core/runtime/exec -run TestDynamicSplit/BlockOnSplit
```
Previously, the test would get stuck when running 10x with race detector.
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Re: [PR] Fix a deadlock situation for BlockOnSplit test case. [beam]
Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.
github-actions[bot] commented on PR #36226:
URL: https://github.com/apache/beam/pull/36226#issuecomment-3315494740
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R: @jrmccluskey for label go.
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Re: [PR] Fix a deadlock situation for BlockOnSplit test case. [beam]
Posted by "jrmccluskey (via GitHub)" <gi...@apache.org>.
jrmccluskey merged PR #36226:
URL: https://github.com/apache/beam/pull/36226
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