[wip][prism] missed lock in ProcessingTimeNow

[stankiewicz]

stageRefreshQueue requires external synchronisation.

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[gemini-code-assist]

Summary of Changes

Hello @stankiewicz, 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 addresses a critical concurrency issue within the Prism runner's ProcessingTimeNow function. By introducing proper synchronization around the access to the internal processing time event queue, it eliminates potential race conditions and ensures data integrity, particularly where stageRefreshQueue relies on external synchronization.

Highlights

• Concurrency Fix: Added a mutex lock (em.refreshCond.L.Lock() and em.refreshCond.L.Unlock()) around the em.processTimeEvents.Peek() call within the ProcessingTimeNow function to ensure thread-safe access to the processTimeEvents queue.

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[stankiewicz]

R: @shunping

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 36.24%. Comparing base (4e0dbb9) to head (c6e3b28).
⚠️ Report is 33 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #36662   +/-   ##
=========================================
  Coverage     36.24%   36.24%           
  Complexity     1666     1666           
=========================================
  Files          1060     1059    -1     
  Lines        165700   165722   +22     
  Branches       1195     1195           
=========================================
+ Hits          60063    60074   +11     
- Misses       103461   103472   +11     
  Partials       2176     2176           

Flag	Coverage Δ
python	40.51% <ø> (+<0.01%)	⬆️

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[shunping]

I think one of the tests timeout because a deadlock occurs after the code change.

[shunping]

I think one of the tests timeout because a deadlock occurs after the code change.

We cannot add the lock in processingTimeNow() because it is called with the refreshCond.L lock in some other places. e.g.

beam/sdks/go/pkg/beam/runners/prism/internal/engine/elementmanager.go

Lines 399 to 401 in b976b51

	em.refreshCond.L.Lock()
	// Check if processing time has advanced before the wait loop.
	emNow := em.ProcessingTimeNow()