Don't start shutdown hook threads more than once.

components/net/sf/briar/lifecycle/ShutdownManagerImpl.java

@@ -15,14 +15,18 @@ class ShutdownManagerImpl implements ShutdownManager {
 		hooks = new HashMap<Integer, Thread>();
 	}
 
-	public synchronized int addShutdownHook(Runnable runnable) {
+	public synchronized int addShutdownHook(Runnable r) {
 		int handle = nextHandle++;
-		Thread hook = new Thread(runnable);
+		Thread hook = createThread(r);
 		hooks.put(handle, hook);
 		Runtime.getRuntime().addShutdownHook(hook);
 		return handle;
 	}
 
+	protected Thread createThread(Runnable r) {
+		return new Thread(r);
+	}
+
 	public synchronized boolean removeShutdownHook(int handle) {
 		Thread hook = hooks.remove(handle);
 		if(hook == null) return false;

components/net/sf/briar/lifecycle/WindowsShutdownManagerImpl.java

@@ -45,9 +45,14 @@ class WindowsShutdownManagerImpl extends ShutdownManagerImpl {
 	}
 
 	@Override
-	public synchronized int addShutdownHook(Runnable runnable) {
+	public synchronized int addShutdownHook(Runnable r) {
 		if(!initialised) initialise();
-		return super.addShutdownHook(new RunOnce(runnable));
+		return super.addShutdownHook(r);
+	}
+
+	@Override
+	protected Thread createThread(Runnable r) {
+		return new StartOnce(r);
 	}
 
 	// Locking: this
@@ -122,19 +127,18 @@ class WindowsShutdownManagerImpl extends ShutdownManagerImpl {
 		}
 	}
 
-	private static class RunOnce implements Runnable {
+	private static class StartOnce extends Thread {
 
-		private final Runnable runnable;
 		private final AtomicBoolean called = new AtomicBoolean(false);
 
-		private RunOnce(Runnable runnable) {
-			this.runnable = runnable;
+		private StartOnce(Runnable r) {
+			super(r);
 		}
 
-		public void run() {
-			// Ensure the runnable only runs once
-			if(called.getAndSet(true)) return;
-			runnable.run();
+		@Override
+		public void start() {
+			// Ensure the thread is only started once
+			if(!called.getAndSet(true)) super.start();
 		}
 	}