👀 Views: 1504 💬 Answers: 1 📅 Created: 2025-06-12

java concurrency concurrent-hashmap Java

I've spent hours debugging this and Could someone explain I'm stuck trying to Quick question that's been bugging me - I'm working on a project and hit a roadblock. I've been struggling with this for a few days now and could really use some help. I'm working with a deadlock scenario in my Java 17 application where I'm using a `ConcurrentHashMap` along with synchronized blocks to manage access to a shared resource. The expected behavior is that my threads should be able to access different keys concurrently without blocking each other, but occasionally, I run into a `java.lang.IllegalMonitorStateException` when trying to enter a synchronized block. Here's a simplified version of what I'm doing: ```java import java.util.concurrent.ConcurrentHashMap; public class SharedResource { private final ConcurrentHashMap<Integer, String> map = new ConcurrentHashMap<>(); public void putValue(Integer key, String value) { synchronized (this) { // This is where the scenario seems to arise map.put(key, value); } } public String getValue(Integer key) { return map.get(key); } } ``` I have multiple threads trying to add values to the `map`, and sometimes, when a thread is inside the `putValue` method and waiting to acquire a lock, I receive the `IllegalMonitorStateException`. I've tried removing the synchronization, but then I run into issues where values are not being written correctly due to race conditions. I've considered using `ReentrantLock`, but I'm not sure if that would be a better approach. Can someone guide to understand why I'm working with this exception and provide guidance on how to properly handle concurrency with `ConcurrentHashMap`? Is synchronized really necessary here, or am I missing a better pattern to manage access? For context: I'm using Java on macOS. What's the best practice here? This is my first time working with Java 3.9. Any suggestions would be helpful. Is there a better approach? What would be the recommended way to handle this? The project is a microservice built with Java.