I have an object with a method named StartDownload()
, that starts three threads.
How do I get a notification when each thread has finished executing?
Is there a way to know if one (or all) of the thread is finished or is still executing?
There are a number of ways you can do this:
How to implement Idea #5? Well, one way is to first create an interface:
public interface ThreadCompleteListener {
void notifyOfThreadComplete(final Thread thread);
}
then create the following class:
public abstract class NotifyingThread extends Thread {
private final Set<ThreadCompleteListener> listeners
= new CopyOnWriteArraySet<ThreadCompleteListener>();
public final void addListener(final ThreadCompleteListener listener) {
listeners.add(listener);
}
public final void removeListener(final ThreadCompleteListener listener) {
listeners.remove(listener);
}
private final void notifyListeners() {
for (ThreadCompleteListener listener : listeners) {
listener.notifyOfThreadComplete(this);
}
}
@Override
public final void run() {
try {
doRun();
} finally {
notifyListeners();
}
}
public abstract void doRun();
}
and then each of your Threads will extend NotifyingThread
and instead of implementing run()
it will implement doRun()
. Thus when they complete, they will automatically notify anyone waiting for notification.
Finally, in your main class -- the one that starts all the Threads (or at least the object waiting for notification) -- modify that class to implement ThreadCompleteListener
and immediately after creating each Thread add itself to the list of listeners:
NotifyingThread thread1 = new OneOfYourThreads();
thread1.addListener(this); // add ourselves as a listener
thread1.start(); // Start the Thread
then, as each Thread exits, your notifyOfThreadComplete
method will be invoked with the Thread instance that just completed (or crashed).
Note that better would be to implements Runnable
rather than extends Thread
for NotifyingThread
as extending Thread is usually discouraged in new code. But I'm coding to your question. If you change the NotifyingThread
class to implement Runnable
then you have to change some of your code that manages Threads, which is pretty straightforward to do.