Raju Gupta created KAFKA-18852: ---------------------------------- Summary: ApiVersions should use Concurrent Collections instead of sychronised Key: KAFKA-18852 URL: https://issues.apache.org/jira/browse/KAFKA-18852 Project: Kafka Issue Type: Improvement Components: clients Reporter: Raju Gupta
h3. Analysis of the Changes in the {{ApiVersions}} Class The changes made to the {{ApiVersions}} class aim to improve thread safety and performance by leveraging concurrent data structures and atomic variables. Below is a detailed analysis of the changes and their implications: ---- h3. *1. Use of {{ConcurrentHashMap}} for {{nodeApiVersions}}* * *Before:* The {{nodeApiVersions}} map was implemented using a {{{}HashMap{}}}, which is not thread-safe. To ensure thread safety, all methods accessing or modifying this map were synchronized. * *After:* The {{HashMap}} has been replaced with a {{{}ConcurrentHashMap{}}}, which is inherently thread-safe. This eliminates the need for explicit synchronization when accessing or modifying the map. *Benefits:* * *Improved Performance:* {{ConcurrentHashMap}} allows concurrent read and write operations without blocking, which can significantly improve performance in multi-threaded environments. * *Simplified Code:* The removal of {{synchronized}} blocks reduces code complexity and potential bottlenecks caused by lock contention. *Considerations:* * *Consistency:* While {{ConcurrentHashMap}} ensures thread safety for individual operations, compound operations (e.g., check-then-act) may still require additional synchronization. However, in this case, the operations are simple (e.g., {{{}put{}}}, {{{}remove{}}}, {{{}get{}}}), so no additional synchronization is needed. ---- h3. *2. Use of {{AtomicLong}} for {{maxFinalizedFeaturesEpoch}}* * *Before:* The {{maxFinalizedFeaturesEpoch}} field was a {{long}} type, and its updates were synchronized to ensure thread safety. * *After:* The {{long}} type has been replaced with an {{{}AtomicLong{}}}, which provides atomic operations for thread-safe updates. *Benefits:* * *Atomic Updates:* {{AtomicLong}} ensures that updates to {{maxFinalizedFeaturesEpoch}} are atomic, eliminating the need for explicit synchronization. * *Improved Performance:* Atomic variables are generally faster than synchronized blocks because they use low-level CPU instructions (e.g., compare-and-swap) instead of locks. *Considerations:* * *Visibility:* {{AtomicLong}} ensures visibility of changes across threads, so there is no need for additional synchronization or {{volatile}} keywords. ---- h3. *3. Removal of {{synchronized}} Blocks* * *Before:* All methods were synchronized to ensure thread safety, which could lead to contention and reduced performance in high-concurrency scenarios. * *After:* The {{synchronized}} keyword has been removed from all methods, as thread safety is now ensured by {{ConcurrentHashMap}} and {{{}AtomicLong{}}}. *Benefits:* * *Reduced Lock Contention:* Removing {{synchronized}} blocks reduces the likelihood of threads blocking each other, improving scalability. * *Simplified Code:* The code is cleaner and easier to maintain without explicit synchronization. *Considerations:* * *Thread Safety:* The thread safety of the class now relies entirely on the correct usage of {{ConcurrentHashMap}} and {{{}AtomicLong{}}}. Any future modifications to the class must ensure that these data structures are used appropriately. ---- h3. *4. Handling of {{finalizedFeatures}}* * The {{finalizedFeatures}} field is still a regular {{{}Map<String, Short>{}}}, and its updates are not atomic. However, in the {{update}} method, it is updated only when {{maxFinalizedFeaturesEpoch}} is updated, which is atomic. *Potential Issues:* * *Race Conditions:* If multiple threads call the {{update}} method simultaneously, there could be a race condition when updating {{{}finalizedFeatures{}}}. For example, one thread might overwrite the changes made by another thread. *Recommendation:* * To ensure thread safety for {{{}finalizedFeatures{}}}, consider using a thread-safe data structure like {{ConcurrentHashMap}} or wrapping the map in {{{}Collections.synchronizedMap(){}}}. Alternatively, you could use an atomic reference ({{{}AtomicReference<Map<String, Short>>{}}}) to ensure atomic updates. ---- h3. *Impact of the Changes* * *Thread Safety:* The class is now thread-safe due to the use of {{ConcurrentHashMap}} and {{{}AtomicLong{}}}. * *Performance:* The removal of {{synchronized}} blocks and the use of concurrent data structures should improve performance in multi-threaded environments. * *Scalability:* The changes make the class more scalable, as concurrent access is now handled more efficiently. ---- h3. *Final Recommendations* # *Address {{finalizedFeatures}} Race Condition:* Ensure that updates to {{finalizedFeatures}} are thread-safe, either by using a concurrent data structure or atomic references. # *Testing:* Thoroughly test the class in high-concurrency scenarios to ensure that all edge cases are handled correctly. # *Documentation:* Update the class documentation to reflect the thread-safety guarantees and the use of concurrent data structures. ---- h3. *Updated Code with {{finalizedFeatures}} Fix* ### **Updated Code with `finalizedFeatures` Fix** Here’s an updated version of the code that addresses the potential race condition with `finalizedFeatures`: ```java private final Map<String, NodeApiVersions> nodeApiVersions = new ConcurrentHashMap<>(); private final AtomicLong maxFinalizedFeaturesEpoch = new AtomicLong(-1); private final AtomicReference<Map<String, Short>> finalizedFeatures = new AtomicReference<>(new ConcurrentHashMap<>()); public void update(String nodeId, NodeApiVersions nodeApiVersions) { this.nodeApiVersions.put(nodeId, nodeApiVersions); if (maxFinalizedFeaturesEpoch.get() < nodeApiVersions.finalizedFeaturesEpoch()) { this.maxFinalizedFeaturesEpoch.set(nodeApiVersions.finalizedFeaturesEpoch()); this.finalizedFeatures.set(new ConcurrentHashMap<>(nodeApiVersions.finalizedFeatures())); } } public void remove(String nodeId) { this.nodeApiVersions.remove(nodeId); } public NodeApiVersions get(String nodeId) { return this.nodeApiVersions.get(nodeId); } public long getMaxFinalizedFeaturesEpoch() { return maxFinalizedFeaturesEpoch.get(); } public FinalizedFeaturesInfo getFinalizedFeaturesInfo() { return new FinalizedFeaturesInfo(maxFinalizedFeaturesEpoch.get(), finalizedFeatures.get()); } -- This message was sent by Atlassian Jira (v8.20.10#820010)