Java Concurrency: Deadlock Occurs When Using Multiple Threads to Update Shared Resource
I'm working on a project and hit a roadblock. I'm optimizing some code but I'm learning this framework and I'm encountering a deadlock issue in my Java application when trying to update a shared resource from multiple threads. I'm using Java 11 and the `ExecutorService` framework for managing my threads. Specifically, I have two threads that need to acquire locks on two different resources, but they sometimes end up waiting indefinitely. Here's a simplified version of my code: ```java public class SharedResource { private final Object lockA = new Object(); private final Object lockB = new Object(); public void updateResources() { synchronized (lockA) { System.out.println(Thread.currentThread().getName() + " acquired lockA"); try { Thread.sleep(100); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } synchronized (lockB) { System.out.println(Thread.currentThread().getName() + " acquired lockB"); } } } } public class DeadlockDemo { public static void main(String[] args) { SharedResource resource = new SharedResource(); ExecutorService executor = Executors.newFixedThreadPool(2); executor.submit(resource::updateResources); executor.submit(resource::updateResources); executor.shutdown(); } } ``` When I run this code, sometimes I get a deadlock situation where both threads are waiting for each other to release their respective locks. I've tried using the `Thread.getState()` method to diagnose the issue, and sure enough, the threads are both in a blocked state. I understand that the typical solution involves lock ordering or using `java.util.concurrent` constructs, but Iām unsure how to refactor my code effectively. What strategies can I employ to prevent this deadlock? Should I consider using ReentrantLock with a timeout, or is there a better approach? Any advice would be greatly appreciated! I'm on Ubuntu 22.04 using the latest version of Java. Is this even possible? For reference, this is a production mobile app. What's the correct way to implement this? For context: I'm using Java on macOS. What's the best practice here?