implemented feature as requested by Kay, Skadi is now a singleton app…

…lication, when a second instance is launched, it will send a message to the first which will then request window focus. The second instance will terminate after sending the message.

src/main/java/eu/over9000/skadi/SkadiMain.java

@@ -21,6 +21,14 @@
  ******************************************************************************/
 package eu.over9000.skadi;
 
+import java.awt.Frame;
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+import java.net.SocketException;
+import java.util.Arrays;
+
 import eu.over9000.skadi.channel.Channel;
 import eu.over9000.skadi.channel.ChannelManager;
 import eu.over9000.skadi.channel.ChannelUpdater;
@@ -39,9 +47,14 @@
 public class SkadiMain {
 
 	public static final String CLIENT_ID = "i2uu9j43ure9x7n4ojpgg4hvcnw6y91";
+	private static final int SKADI_LOCKING_PORT = 37973;
+
+	private DatagramSocket lockingSocket;
 
 	private static SkadiMain instance;
 
+	private static final byte[] WAKEUP_SIGNATURE = "SKADI".getBytes();
+
 	private final boolean isLinux = System.getProperty("os.name").equals("Linux");
 
 	public String chrome_exec = this.isLinux ? "chromium-browser"
@@ -53,6 +66,7 @@ public class SkadiMain {
 	public boolean use_livestreamer = true;
 	public boolean display_notifications = true;
 	public boolean minimize_to_tray = false;
+	private Thread wakeupReceiverThread;
 
 	public static SkadiMain getInstance() {
 		if (SkadiMain.instance == null) {
@@ -66,6 +80,13 @@ public static void main(final String[] args) {
 	}
 
 	private void runInit(final String[] args) {
+
+		if (!this.createSocketLock()) {
+			System.out.println("could not create socket on port " + SkadiMain.SKADI_LOCKING_PORT
+			        + " (Skadi already running?), exiting.");
+			return;
+		}
+
 		this.addShutdownHook();
 
 		ChannelManager.getInstance();
@@ -81,6 +102,56 @@ private void runInit(final String[] args) {
 
 	}
 
+	private boolean createSocketLock() {
+		try {
+			this.lockingSocket = new DatagramSocket(SkadiMain.SKADI_LOCKING_PORT, InetAddress.getLoopbackAddress());
+			this.wakeupReceiverThread = new Thread(new Runnable() {
+
+				@Override
+				public void run() {
+					while ((SkadiMain.this.lockingSocket != null) && !SkadiMain.this.lockingSocket.isClosed()) {
+						final byte[] buffer = new byte[SkadiMain.WAKEUP_SIGNATURE.length];
+
+						final DatagramPacket incoming = new DatagramPacket(buffer, buffer.length);
+						try {
+							SkadiMain.this.lockingSocket.receive(incoming);
+
+							if (Arrays.equals(SkadiMain.WAKEUP_SIGNATURE, incoming.getData())) {
+								SkadiGUI.getInstance().setVisible(true);
+								SkadiGUI.getInstance().setState(Frame.NORMAL);
+								SkadiGUI.getInstance().toFront();
+								SkadiLogging.log("received wakeup on locking socket");
+							}
+
+						} catch (final IOException e) {
+							if ((SkadiMain.this.lockingSocket == null) || SkadiMain.this.lockingSocket.isClosed()) {
+								return;
+							}
+							e.printStackTrace();
+						}
+					}
+
+				}
+			}, "SkadiWakeupReceiver");
+
+			this.wakeupReceiverThread.start();
+		} catch (final SocketException e) {
+			try {
+				final DatagramSocket sendWakeupSocket = new DatagramSocket(0, InetAddress.getLoopbackAddress());
+
+				final DatagramPacket sendWakeupPacket = new DatagramPacket(SkadiMain.WAKEUP_SIGNATURE,
+				        SkadiMain.WAKEUP_SIGNATURE.length, InetAddress.getLoopbackAddress(),
+				        SkadiMain.SKADI_LOCKING_PORT);
+				sendWakeupSocket.send(sendWakeupPacket);
+				sendWakeupSocket.close();
+			} catch (final IOException e1) {
+				e1.printStackTrace();
+			}
+		}
+
+		return this.lockingSocket != null;
+	}
+
 	private void addShutdownHook() {
 		Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
 
@@ -94,8 +165,14 @@ public void run() {
 				}
 				SkadiLogging.log("SAVING DATA..");
 				PersistenceManager.getInstance().saveData();
-				SkadiLogging.log("SHUTDOWN COMPLETE");
 
+				if (SkadiMain.this.lockingSocket != null) {
+					SkadiLogging.log("RELEASING LOCK..");
+					SkadiMain.this.wakeupReceiverThread.interrupt();
+					SkadiMain.this.lockingSocket.close();
+				}
+
+				SkadiLogging.log("SHUTDOWN COMPLETE");
 			}
 		}));
 	}