Java 11: Thread Safety Issues When Using ConcurrentHashMap with Custom Objects
This might be a silly question, but I'm deploying to production and I recently switched to I'm building a feature where I'm facing a challenging issue while working with a `ConcurrentHashMap` in Java 11 where I'm storing custom objects as values. I noticed that under heavy concurrent access, my objects seem to get corrupted, leading to inconsistent state. Specifically, I have a custom class `UserSession` which has a `String` field for `sessionId` and a `Map<String, String>` for `attributes`. Here's a simplified version of my code: ```java import java.util.concurrent.ConcurrentHashMap; import java.util.Map; public class SessionManager { private final ConcurrentHashMap<String, UserSession> sessions = new ConcurrentHashMap<>(); public void addSession(String sessionId, UserSession session) { sessions.put(sessionId, session); } public UserSession getSession(String sessionId) { return sessions.get(sessionId); } } class UserSession { private String sessionId; private Map<String, String> attributes; public UserSession(String sessionId) { this.sessionId = sessionId; this.attributes = new ConcurrentHashMap<>(); } public void setAttribute(String key, String value) { attributes.put(key, value); } public String getAttribute(String key) { return attributes.get(key); } } ``` I perform multiple writes to `attributes` from different threads, using the `setAttribute` method. However, sometimes when I retrieve the session using `getSession`, the values of `attributes` appear to be missing or null, even though they should have been set. I've tried synchronizing the `setAttribute` method, but it severely impacts performance. Here’s how I tried doing it: ```java public synchronized void setAttribute(String key, String value) { attributes.put(key, value); } ``` This leads to significant latency under high load. I'm also considering whether using a `ThreadLocal` might help, but I'm unsure if that's the right approach for my use case. Additionally, I've checked for any potential threading issues using tools like IntelliJ's Thread Analyzer, but didn't find anything obvious. Has anyone experienced similar issues with `ConcurrentHashMap` and custom objects? What would be the best approach to ensure thread safety without sacrificing performance? Any ideas how to fix this? I'm working with Java in a Docker container on Windows 11. Is there a simpler solution I'm overlooking? I'm developing on Linux with Java. Any pointers in the right direction? For reference, this is a production web app. Any suggestions would be helpful.