Only allow a single program instance to be run.

Creates a ServerSocket instance on a port (default: 49250).
Credits to marcostudios for the suggestion.

Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>

src/itdelatrisu/opsu/Opsu.java

@@ -29,7 +29,9 @@ import itdelatrisu.opsu.states.SongMenu;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
+import java.io.IOException;
 import java.io.PrintStream;
+import java.net.ServerSocket;
 
 import org.newdawn.slick.AppGameContainer;
 import org.newdawn.slick.Color;
@@ -66,6 +68,11 @@ public class Opsu extends StateBasedGame {
 		STATE_GAMEPAUSEMENU = 6,
 		STATE_GAMERANKING   = 7;
 
+	/**
+	 * Used to restrict the program to a single instance.
+	 */
+	private static ServerSocket SERVER_SOCKET;
+
 	public Opsu(String name) {
 		super(name);
 	}
@@ -82,12 +89,6 @@ public class Opsu extends StateBasedGame {
 	}
 
 	public static void main(String[] args) {
-		// set path for lwjgl natives - NOT NEEDED if using JarSplice
-//		System.setProperty("org.lwjgl.librarypath", new File("native").getAbsolutePath());
-
-		// set the resource path
-		ResourceLoader.addResourceLocation(new FileSystemLocation(new File("./res/")));
-
 		// log all errors to a file
 		Log.setVerbose(false);
 		try {
@@ -102,13 +103,29 @@ public class Opsu extends StateBasedGame {
 			}
 		});
 
+		// parse configuration file
+		Options.parseOptions();
+
+		// only allow a single instance
+		try {
+			SERVER_SOCKET = new ServerSocket(Options.getPort());
+		} catch (IOException e) {
+			Log.error(String.format("Another program is already running on port %d.", Options.getPort()), e);
+			System.exit(1);
+		}
+
+		// set path for lwjgl natives - NOT NEEDED if using JarSplice
+//		System.setProperty("org.lwjgl.librarypath", new File("native").getAbsolutePath());
+
+		// set the resource path
+		ResourceLoader.addResourceLocation(new FileSystemLocation(new File("./res/")));
+
 		// start the game
 		Opsu osuGame = new Opsu("opsu!");
 		try {
 			AppGameContainer app = new AppGameContainer(osuGame);
 
 			// basic game settings
-			Options.parseOptions();
 			int[] containerSize = Options.getContainerSize();
 			app.setDisplayMode(containerSize[0], containerSize[1], false);
 			String[] icons = { "icon16.png", "icon32.png" };
@@ -147,6 +164,18 @@ public class Opsu extends StateBasedGame {
 
 		Options.saveOptions();
 		((AppGameContainer) this.getContainer()).destroy();
+		closeSocket();
 		return true;
 	}
+
+	/**
+	 * Closes the server socket.
+	 */
+	public static void closeSocket() {
+		try {
+			SERVER_SOCKET.close();
+		} catch (IOException e) {
+			Log.error("Failed to close server socket.", e);
+		}
+	}
 }

src/itdelatrisu/opsu/states/MainMenuExit.java

@@ -131,6 +131,7 @@ public class MainMenuExit extends BasicGameState {
 
 		if (yesButton.contains(x, y)) {
 			Options.saveOptions();
+			Opsu.closeSocket();
 			container.exit();
 		} else if (noButton.contains(x, y))
 			game.enterState(Opsu.STATE_MAINMENU, new EmptyTransition(), new FadeInTransition(Color.black));
@@ -141,6 +142,7 @@ public class MainMenuExit extends BasicGameState {
 		switch (key) {
 		case Input.KEY_1:
 			Options.saveOptions();
+			Opsu.closeSocket();
 			container.exit();
 			break;
 		case Input.KEY_2:

src/itdelatrisu/opsu/states/Options.java

@@ -225,6 +225,11 @@ public class Options extends BasicGameState {
 	 */
 	private static int screenshotFormatIndex = 0;
 
+	/**
+	 * Port binding.
+	 */
+	private static int port = 0;
+
 	/**
 	 * Back button (shared by other states).
 	 */
@@ -673,6 +678,19 @@ public class Options extends BasicGameState {
 	 */
 	public static boolean isComboBurstEnabled() { return showComboBursts; }
 
+	/**
+	 * Returns the port number to bind to.
+	 * @return the port
+	 */
+	public static int getPort() {
+		if (port == 0) {
+			// choose a random port
+			port = 49250;
+			optionsChanged = true;  // force file creation
+		}
+		return port;
+	}
+
 	/**
 	 * Returns the current beatmap directory.
 	 * If invalid, this will attempt to search for the directory,
@@ -761,6 +779,11 @@ public class Options extends BasicGameState {
 				case "ComboBurst":
 					showComboBursts = Boolean.parseBoolean(value);
 					break;
+				case "Port":
+					i = Integer.parseInt(value);
+					if (i > 0 && i <= 65535)
+						port = i;
+					break;
 				}
 			}
 		} catch (IOException e) {
@@ -814,6 +837,8 @@ public class Options extends BasicGameState {
 			writer.newLine();
 			writer.write(String.format("ComboBurst = %b", showComboBursts));
 			writer.newLine();
+			writer.write(String.format("Port = %d", port));
+			writer.newLine();
 			writer.close();
 		} catch (IOException e) {
 			Log.error(String.format("Failed to write to file '%s'.", OPTIONS_FILE), e);