How Can Java Executors Handle Asynchronous Task Completion Notifications Without Blocking?

Java Executors: Asynchronous Task Completion Notification

In a scenario where multiple queues hold tasks to be executed sequentially by an executor service, blocking operations can consume excessive stack space. To mitigate this issue, a non-blocking approach is desired.

One solution involves defining a callback interface with methods to process results and pass necessary parameters. This interface can be implemented in a wrapper class for Runnable tasks, which are then submitted to the executor service. Upon task completion, the callback interface is invoked.

interface Callback {
  void complete();
}

class CallbackTask implements Runnable {
  private final Runnable task;
  private final Callback callback;

  CallbackTask(Runnable task, Callback callback) {
    this.task = task;
    this.callback = callback;
  }

  public void run() {
    task.run();
    callback.complete();
  }
}

Alternatively, Java 8 introduces CompletableFuture, which provides mechanisms for asynchronous task composition and conditional processing. Here's an example using CompletableFuture:

CompletableFuture<String> f = CompletableFuture.supplyAsync(() -> ExampleService.work());
f.thenAccept(listener::notify);

In this example, ExampleService.work() is the task to be executed asynchronously. The notify method is the callback that will be invoked when the task is complete.

Using these techniques, tasks can be submitted to an executor service without blocking, allowing for efficient processing of large queues while avoiding stack space exhaustion.

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