Ensuring Thread Completion with Notification

In multithreaded applications, monitoring the completion status of threads is crucial to ensure proper execution. This article explores various methods to obtain notifications when threads have finished executing.

Tracking Thread Status

One approach is to use Thread.join(), which blocks the main thread until all specified threads have completed. While effective, it may not always be desirable for asynchronous scenarios.

Another option is Thread.isAlive(), but constant polling for thread completion is generally discouraged as it introduces overhead and potential performance issues.

Custom Notification Mechanisms

Unorthodox approaches include setting uncaught exception handlers or using locks and synchronizers. However, these methods can be complex and prone to errors.

Listener-Based Notification

A more structured solution is to create a listener interface and notify it from each thread upon completion. This involves creating an interface like ThreadCompleteListener and a class like NotifyingThread that extends from Thread and notifies listeners when it completes.

The main class can implement ThreadCompleteListener and add itself as a listener to each thread to receive notifications of thread completion.

Example Implementation

Below is an example implementation of the listener-based approach:

public interface ThreadCompleteListener {
    void notifyOfThreadComplete(final Thread thread);
}

public abstract class NotifyingThread extends Thread {
    // Listener management
    ...

    // Notify listeners
    ...

    @Override
    public final void run() {
        try {
            doRun();
        } finally {
            notifyListeners();
        }
    }

    public abstract void doRun();
}

Usage in Main Class

NotifyingThread thread1 = new OneOfYourThreads();
thread1.addListener(this); // add ourselves as a listener
thread1.start();           // Start the Thread

This approach provides a flexible and structured way to manage thread completion and receive notifications in a timely manner.