Java 11 CompletableFuture not completing as expected when using multiple dependent tasks
I tried several approaches but none seem to work... I'm working on a personal project and I've been researching this but I've spent hours debugging this and I'm testing a new approach and I'm working on a personal project and I'm working on a personal project and I'm having an issue with `CompletableFuture` in Java 11 where dependent tasks are not completing in the expected order... I have a series of tasks that depend on the results of previous tasks, but it seems that they are getting executed in an unexpected sequence, leading to `NoSuchElementException` in my final processing step. Here's a simplified version of what I'm trying to accomplish: ```java import java.util.concurrent.CompletableFuture; import java.util.concurrent.ExecutionException; public class CompletableFutureExample { public static void main(String[] args) throws ExecutionException, InterruptedException { CompletableFuture<Integer> future1 = CompletableFuture.supplyAsync(() -> { try { Thread.sleep(100); } catch (InterruptedException e) {} // Simulating delay return 1; }); CompletableFuture<Integer> future2 = future1.thenApply(result -> { if (result == null) throw new NoSuchElementException("Result is null"); return result + 2; }); CompletableFuture<Integer> future3 = future2.thenApply(result -> result + 3); System.out.println("Final Result: " + future3.get()); } } ``` Despite the sequential dependency, I sometimes get a `NoSuchElementException` which indicates that `future1`'s result isn't as expected. I've checked the logic and it seems to return `1` as intended, but I suspect that there might be an issue with how the tasks are scheduled. I've attempted to add debugging statements within each stage to ensure they complete properly, and logging shows that `future1` is indeed completing before `future2` starts. However, I still encounter this exception intermittently. I've also considered using `join()` instead of `get()`, but it doesn't seem to address the underlying issue. Is there a best practice for handling these dependent `CompletableFuture` tasks to ensure that the execution order is maintained, or could there be an underlying concurrency issue that I'm overlooking? Am I missing something obvious? What's the best practice here? The project is a CLI tool built with Java. Any help would be greatly appreciated! I'm working in a Linux environment. Is this even possible? What would be the recommended way to handle this? What are your experiences with this?