Java 11: Unexpected Behavior When Using CompletableFuture with Custom Executor
This might be a silly question, but I'm relatively new to this, so bear with me... I'm dealing with I'm working on a project and hit a roadblock. I'm experiencing unexpected behavior when using `CompletableFuture` with a custom `Executor` in Java 11. I have a situation where I'm trying to parallelize some I/O-bound tasks, but it seems like my tasks are not running concurrently as I expect. Here’s a simplified version of my code: ```java import java.util.concurrent.CompletableFuture; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class CompletableFutureExample { public static void main(String[] args) { ExecutorService executor = Executors.newFixedThreadPool(2); CompletableFuture<Void> future1 = CompletableFuture.runAsync(() -> { try { Thread.sleep(2000); System.out.println("Task 1 completed"); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } }, executor); CompletableFuture<Void> future2 = CompletableFuture.runAsync(() -> { try { Thread.sleep(1000); System.out.println("Task 2 completed"); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } }, executor); CompletableFuture<Void> combinedFuture = CompletableFuture.allOf(future1, future2); combinedFuture.join(); executor.shutdown(); } } ``` When I run this code, I observe that the output indicates "Task 2 completed" almost immediately, but "Task 1 completed" always appears after a 2-second delay, as expected. However, I expected both tasks to be running concurrently and finishing around the same time, yet they seem to be serialized instead. I’ve confirmed that my thread pool is correctly set with two threads. I even increased the pool size and made sure that no other parts of my application are blocking the threads. Additionally, I tried using `CompletableFuture.supplyAsync()` instead of `runAsync()` but encountered the same behavior. Is there something I'm missing, or is there a known issue with `CompletableFuture` in this context? Any insights would be greatly appreciated. I'm working in a Windows 11 environment. What's the best practice here? I've been using Java for about a year now. Is there a better approach? What's the correct way to implement this? I'm coming from a different tech stack and learning Java. How would you solve this?