Make the manual asynchronous worker closable.

Added a good deal of synchronization to deal with closing a 
specific worker. This overhead can be avoided by simply closing 
any given worker.

ProtocolLib/src/com/comphenix/protocol/async/AsyncListenerHandler.java

@@ -1,6 +1,9 @@
 package com.comphenix.protocol.async;
 
+import java.util.HashSet;
+import java.util.Set;
 import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.logging.Level;
 
@@ -18,18 +21,26 @@ import com.comphenix.protocol.events.PacketListener;
 public class AsyncListenerHandler {
 
 	/**
-	 * Signal an end to the packet processing.
+	 * Signal an end to packet processing.
 	 */
 	private static final PacketEvent INTERUPT_PACKET = new PacketEvent(new Object());
 	
+	/**
+	 * Called when the threads have to wake up for something important.
+	 */
+	private static final PacketEvent WAKEUP_PACKET = new PacketEvent(new Object());
+	
 	// Default queue capacity
 	private static int DEFAULT_CAPACITY = 1024;
 	
 	// Cancel the async handler
 	private volatile boolean cancelled;
 	
-	// If we've started the listener loop before
-	private AtomicInteger started = new AtomicInteger();
+	// Number of worker threads
+	private final AtomicInteger started = new AtomicInteger();
+	
+	// Unique local worker ID
+	private final AtomicInteger nextID = new AtomicInteger();
 	
 	// The packet listener
 	private PacketListener listener;
@@ -41,6 +52,10 @@ public class AsyncListenerHandler {
 	// List of queued packets
 	private ArrayBlockingQueue<PacketEvent> queuedPackets = new ArrayBlockingQueue<PacketEvent>(DEFAULT_CAPACITY);
 
+	// List of cancelled tasks
+	private final Set<Integer> stoppedTasks = new HashSet<Integer>();
+	private final Object stopLock = new Object();
+	
 	// Minecraft main thread
 	private Thread mainThread;
 	
@@ -112,15 +127,57 @@ public class AsyncListenerHandler {
 	}
 	
 	/**
-	 * Create a runnable that will initiate the listener loop.
+	 * Create a worker that will initiate the listener loop. Note that using stop() to
+	 * close a specific worker is less efficient than stopping an arbitrary worker.
 	 * <p>
 	 * <b>Warning</b>: Never call the run() method in the main thread.
 	 */
 	public Runnable getListenerLoop() {
-		return new Runnable() {
+		return new AsyncRunnable() {
+
+			private final AtomicBoolean running = new AtomicBoolean();
+			private volatile int id;
+			
 			@Override
 			public void run() {
-				listenerLoop();
+				// Careful now
+				if (running.compareAndSet(false, true)) {
+					id = nextID.incrementAndGet();
+					listenerLoop(id);
+					
+					synchronized (stopLock) {
+						stoppedTasks.remove(id);
+						notifyAll();
+						running.set(false);
+					}
+					
+				} else {
+					throw new IllegalStateException(
+							"This listener loop has already been started. Create a new instead.");
+				}
+			}
+			
+			@Override
+			public boolean stop() throws InterruptedException {
+				synchronized (stopLock) {
+					if (!running.get())
+						return false;
+
+					stoppedTasks.add(id);
+			
+					// Wake up threads - we have a listener to stop
+					for (int i = 0; i < getWorkers(); i++) {
+						queuedPackets.offer(WAKEUP_PACKET);
+					}
+					
+					waitForStops();
+					return true;
+				}
+			}
+
+			@Override
+			public boolean isRunning() {
+				return running.get();
 			}
 		};
 	}
@@ -128,9 +185,11 @@ public class AsyncListenerHandler {
 	/**
 	 * Start a singler worker thread handling the asynchronous.
 	 */
-	public void start() {
+	public synchronized void start() {
 		if (listener.getPlugin() == null)
 			throw new IllegalArgumentException("Cannot start task without a valid plugin.");
+		if (cancelled)
+			throw new IllegalStateException("Cannot start a worker when the listener is closing.");
 		
 		filterManager.scheduleAsyncTask(listener.getPlugin(), getListenerLoop());
 	}
@@ -139,13 +198,80 @@ public class AsyncListenerHandler {
 	 * Start multiple worker threads for this listener.
 	 * @param count - number of worker threads to start.
 	 */
-	public void start(int count) {
+	public synchronized void start(int count) {
 		for (int i = 0; i < count; i++)
 			start();
 	}
 	
+	/**
+	 * Stop a worker thread.
+	 */
+	public synchronized void stop() {
+		queuedPackets.add(INTERUPT_PACKET);
+	}
+	
+	/**
+	 * Stop the given amount of worker threads.
+	 * @param count - number of threads to stop.
+	 */
+	public synchronized void stop(int count) {
+		for (int i = 0; i < count; i++)
+			stop();
+	}
+	
+	/**
+	 * Set the current number of workers. 
+	 * <p>
+	 * This method can only be called with a count of zero when the listener is closing.
+	 * @param count - new number of workers.
+	 */
+	public synchronized void setWorkers(int count) {
+		if (count < 0)
+			throw new IllegalArgumentException("Number of workers cannot be less than zero.");
+		if (count > DEFAULT_CAPACITY)
+			throw new IllegalArgumentException("Cannot initiate more than " + DEFAULT_CAPACITY + " workers");
+		if (cancelled && count > 0)
+			throw new IllegalArgumentException("Cannot add workers when the listener is closing.");
+		
+		long time = System.currentTimeMillis();
+		
+		// Try to get to the correct count
+		while (started.get() != count) {
+			if (started.get() < count)
+				start();
+			else
+				stop();
+			
+			// May happen if another thread is doing something similar to "setWorkers"
+			if ((System.currentTimeMillis() - time) > 1000)
+				throw new RuntimeException("Failed to set worker count.");
+		}
+	}
+	
+	/**
+	 * Retrieve the current number of registered workers.
+	 * <p>
+	 * Note that the returned value may be out of data.
+	 * @return Number of registered workers.
+	 */
+	public synchronized int getWorkers() {
+		return started.get();
+	}
+	
+	/**
+	 * Wait until every tasks scheduled to stop has actually stopped.
+	 * @return TRUE if the current listener should stop, FALSE otherwise.
+	 * @throws InterruptedException - If the current thread was interrupted.
+	 */
+	private boolean waitForStops() throws InterruptedException {
+		while (stoppedTasks.size() > 0 && !cancelled) {
+			wait();
+		}
+		return cancelled;
+	}
+	
 	// DO NOT call this method from the main thread
-	private void listenerLoop() {
+	private void listenerLoop(int taskID) {
 		
 		// Danger, danger!
 		if (Thread.currentThread().getId() == mainThread.getId()) 
@@ -153,18 +279,34 @@ public class AsyncListenerHandler {
 		if (cancelled)
 			throw new IllegalStateException("Listener has been cancelled. Create a new listener instead.");
 
+		try {
+			// Wait if certain threads are stopping
+			synchronized (stopLock) {
+				if (waitForStops())
+					return;
+			}
+			
 			// Proceed
 			started.incrementAndGet();
 			
-		try {
 			mainLoop:
 			while (!cancelled) {
 				PacketEvent packet = queuedPackets.take();
 				AsyncMarker marker = packet.getAsyncMarker();
 				
 				// Handle cancel requests
-				if (packet == null || marker == null || !packet.isAsynchronous()) {
-					break;
+				if (packet == null || marker == null || packet == INTERUPT_PACKET) {
+					return;
+					
+				} else if (packet == WAKEUP_PACKET) {
+					// This is a bit slow, but it should be safe
+					synchronized (stopLock) {
+						// Are we the one who is supposed to stop?
+						if (stoppedTasks.contains(taskID)) 
+							return;
+						if (waitForStops())
+							return;
+					}
 				}
 				
 				// Here's the core of the asynchronous processing
@@ -221,8 +363,11 @@ public class AsyncListenerHandler {
 	private void stopThreads() {
 		// Poison Pill Shutdown
 		queuedPackets.clear();
+		stop(started.get());
 		
-		for (int i = 0; i < started.get(); i++)
-			queuedPackets.add(INTERUPT_PACKET);
+		// Individual shut down is irrelevant now
+		synchronized (stopLock) {
+			notifyAll();
+		}
 	}
 }

ProtocolLib/src/com/comphenix/protocol/async/AsyncRunnable.java

@@ -0,0 +1,23 @@
+package com.comphenix.protocol.async;
+
+/**
+ * A runnable representing a asynchronous event listener.
+ * 
+ * @author Kristian
+ */
+public interface AsyncRunnable extends Runnable {
+	
+	/**
+	 * Stop the given runnable.
+	 * <p>
+	 * This may not occur right away.
+	 * @return TRUE if the thread was stopped, FALSE if it was already stopped.
+	 */
+	public boolean stop() throws InterruptedException;
+	
+	/**
+	 * Determine if we're running or not.
+	 * @return TRUE if we're running, FALSE otherwise.
+	 */
+	public boolean isRunning();
+}