How to implement guide with concurrenthashmap not behaving as expected in java 11
I need help solving I'm having trouble with After trying multiple solutions online, I still can't figure this out... I'm having trouble with I've searched everywhere and can't find a clear answer. I'm working on a personal project and I'm currently working with a perplexing scenario with `ConcurrentHashMap` in Java 11. I have a multi-threaded application that is supposed to increment a counter each time a specific key is accessed. However, I'm observing that the counts are not being updated correctly, leading to inconsistent results. Here’s a simplified version of my code: ```java import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class CounterExample { private final ConcurrentHashMap<String, Integer> counterMap = new ConcurrentHashMap<>(); public void incrementCounter(String key) { counterMap.merge(key, 1, Integer::sum); } public int getCount(String key) { return counterMap.getOrDefault(key, 0); } public static void main(String[] args) throws InterruptedException { CounterExample example = new CounterExample(); ExecutorService executor = Executors.newFixedThreadPool(5); for (int i = 0; i < 1000; i++) { final String key = "item1"; executor.submit(() -> example.incrementCounter(key)); } executor.shutdown(); executor.awaitTermination(1, TimeUnit.MINUTES); System.out.println("Final count for item1: " + example.getCount("item1")); } } ``` I am submitting 1000 increments concurrently but the final count is often less than 1000. Sometimes it outputs counts like 950 or 970, which is puzzling. I’ve verified that the `merge` method should handle concurrent updates correctly, so I am wondering if there might be an scenario with how the threads are being managed or if there’s a subtle bug in my implementation. Additionally, I've tried replacing the `merge` with a simple `put` method inside a synchronized block, but this drastically reduces performance and still doesn’t guarantee that the count reflects all increments. Has anyone faced a similar question or can suggest a best practice for reliably incrementing values in a concurrent environment using `ConcurrentHashMap`? My development environment is Windows. What am I doing wrong? What's the best practice here? This is for a CLI tool running on Ubuntu 22.04. Am I approaching this the right way? I recently upgraded to Java 3.11. I'd be grateful for any help. I appreciate any insights! This is part of a larger mobile app I'm building.