fix: incorporate feedback from #138 #146
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Summary of Changes
Hello @kabir, 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 focuses on significantly improving the concurrency and thread-safety of several core components within the sdk-server-common module. By adopting modern java.util.concurrent utilities like ConcurrentHashMap, CopyOnWriteArrayList, and Semaphore, the changes aim to enhance the robustness, scalability, and performance of the application in multi-threaded environments, while also streamlining the codebase by eliminating manual synchronization where concurrent collections provide built-in guarantees.
Highlights
- Concurrency Improvements: Migrated several internal data structures from
Collections.synchronizedMapwrappers toConcurrentHashMapacrossInMemoryQueueManager,DefaultRequestHandler, andInMemoryTaskStore. This enhances thread-safety and performance by allowing concurrent access to different segments of the maps without global locking. - Thread-Safe List Implementation: Replaced
ArrayListwithCopyOnWriteArrayListinEnhancedRunnablefor managingDoneCallbackinstances. This provides a thread-safe list that is efficient for scenarios with many reads and infrequent writes, enabling the removal of explicitsynchronizedblocks. - Queue Capacity Management: Introduced a
SemaphoreinEventQueueto precisely control the queue's capacity. This ensures that events are only enqueued when capacity is available and permits are released upon dequeuing, preventing unbounded growth and improving flow control. The underlying queue was also changed toLinkedBlockingDeque. - Simplified Synchronization: Removed redundant
synchronizedblocks fromEnhancedRunnableandInMemoryQueueManageras the newly adopted concurrent data structures (CopyOnWriteArrayList,ConcurrentHashMap) handle thread safety internally, leading to cleaner and potentially more performant code.
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Code Review
This pull request modernizes the concurrency handling by replacing synchronized maps with ConcurrentHashMap and adopting atomic operations. However, there is a critical issue in the new semaphore-based queue capacity logic in EventQueue.java that could lead to unbounded memory growth, and a high-severity issue with InterruptedException handling.
| // Call toString() since for errors we don't really want the full stacktrace | ||
| log.debug("Dequeued event (no wait) {} {}", this, event instanceof Throwable ? event.toString() : event); | ||
| } | ||
| semaphore.release(); |
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The semaphore is released even if queue.poll() returns null (i.e., no event was dequeued). This will cause the semaphore's permit count to increase over time, effectively breaking the intended capacity limit of the queue. This could lead to unbounded memory usage and an OutOfMemoryError. The semaphore.release() call should only be made when an event has been successfully dequeued.
if (event != null) {
semaphore.release();
}| // Call toString() since for errors we don't really want the full stacktrace | ||
| log.debug("Dequeued event (waiting) {} {}", this, event instanceof Throwable ? event.toString() : event); | ||
| } | ||
| semaphore.release(); |
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The semaphore is released even if queue.poll(...) returns null because of a timeout. This will incorrectly increment the semaphore's permit count, defeating the queue's capacity limit and risking an OutOfMemoryError. The semaphore.release() call must be conditional on an event actually being dequeued.
if (event != null) {
semaphore.release();
}| } catch (InterruptedException e) { | ||
| throw new RuntimeException("Unable to acquire the semaphore to enqueue the event", e); |
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When catching an InterruptedException, it is a best practice to restore the interrupted status of the thread by calling Thread.currentThread().interrupt()1. This allows code higher up the call stack to be aware that an interruption occurred and handle it appropriately. Simply wrapping it in a RuntimeException loses this important information.
Thread.currentThread().interrupt();
throw new RuntimeException("Unable to acquire the semaphore to enqueue the event", e);Style Guide References
Footnotes
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Description
Thank you for opening a Pull Request!
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CONTRIBUTINGGuide.fix:which represents bug fixes, and correlates to a SemVer patch.feat:represents a new feature, and correlates to a SemVer minor.feat!:, orfix!:,refactor!:, etc., which represent a breaking change (indicated by the!) and will result in a SemVer major.Fixes #<issue_number_goes_here> 🦕