[DocDB] Fix heap-use-after-free in yb::YBThreadPool #28299
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📌 Summary This PR fixes a heap-use-after-free detected by ASAN in yb::YBThreadPool::Impl::NotifyWorker, where a Worker could be freed while another thread was concurrently accessing it through waiting_workers.Pop(). 🐞 Root Cause Multiple threads could concurrently pop from waiting_workers. A Worker in IdleStop state could be erased and deleted while another thread was still reading it. This resulted in nondeterministic crashes under ASAN and caused the following test to fail: CDCSDKConsumptionConsistentChangesTest. TestLSNDeterminismWithSpecialRecordOnRestartWithPartialAck 🔧 Fix Added waiting_workers_active_pops counter in ThreadPoolShare to track active Pop() operations. Deferred deletion of Worker objects if pops are active, using a new deferred_deletes_ list. Ensured Shutdown() waits for all pops to finish before freeing deferred workers. ✅ Validation Ran ybd asan --cxx-test integration-tests_cdcsdk_consumption_consistent_changes-test — no more heap-use-after-free crashes. Verified that normal enqueue/dequeue behavior is unaffected. Checked that no leaks remain (all deferred deletes are flushed in shutdown). 📊 Impact Fixes flaky ASAN test failures in DocDB thread pool. Minimal overhead: adds two atomic ops per worker notification. No API changes. 🔗 References Fixes: yugabyte#28297 Jira: DB-17979
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📌 Summary
This PR fixes a heap-use-after-free detected by ASAN in yb::YBThreadPool::Impl::NotifyWorker, where a Worker could be freed while another thread was concurrently accessing it through waiting_workers.Pop().
🐞 Root Cause
Multiple threads could concurrently pop from waiting_workers.
A Worker in IdleStop state could be erased and deleted while another thread was still reading it.
This resulted in nondeterministic crashes under ASAN and caused the following test to fail:
CDCSDKConsumptionConsistentChangesTest.
TestLSNDeterminismWithSpecialRecordOnRestartWithPartialAck
🔧 Fix
Added waiting_workers_active_pops counter in ThreadPoolShare to track active Pop() operations.
Deferred deletion of Worker objects if pops are active, using a new deferred_deletes_ list.
Ensured Shutdown() waits for all pops to finish before freeing deferred workers.
✅ Validation
Ran ybd asan --cxx-test integration-tests_cdcsdk_consumption_consistent_changes-test — no more heap-use-after-free crashes.
Verified that normal enqueue/dequeue behavior is unaffected.
Checked that no leaks remain (all deferred deletes are flushed in shutdown).
📊 Impact
Fixes flaky ASAN test failures in DocDB thread pool.
Minimal overhead: adds two atomic ops per worker notification.
No API changes.
🔗 References
Fixes: #28297
Jira: DB-17979