add option to allow multiple instances (closes #33)

src/itdelatrisu/opsu/Opsu.java

@@ -118,18 +118,20 @@ public class Opsu extends StateBasedGame {
 		Options.parseOptions();
 
 		// only allow a single instance
-		try {
-			SERVER_SOCKET = new ServerSocket(Options.getPort(), 1, InetAddress.getLocalHost());
-		} catch (UnknownHostException e) {
-			// shouldn't happen
-		} catch (IOException e) {
-			ErrorHandler.error(String.format(
+		if (!Options.noSingleInstance()) {
+			try {
+				SERVER_SOCKET = new ServerSocket(Options.getPort(), 1, InetAddress.getLocalHost());
+			} catch (UnknownHostException e) {
+				// shouldn't happen
+			} catch (IOException e) {
+				ErrorHandler.error(String.format(
 					"opsu! could not be launched for one of these reasons:\n" +
-					"- An instance of opsu! is already running.\n" +
-					"- Another program is bound to port %d. " +
-					"You can change the port opsu! uses by editing the \"Port\" field in the configuration file.",
+						"- An instance of opsu! is already running.\n" +
+						"- Another program is bound to port %d. " +
+						"You can change the port opsu! uses by editing the \"Port\" field in the configuration file.",
 					Options.getPort()), null, false);
-			System.exit(1);
+				System.exit(1);
+			}
 		}
 
 		File nativeDir;

src/itdelatrisu/opsu/Options.java

@@ -134,6 +134,8 @@ public class Options {
 	/** Port binding. */
 	private static int port = 49250;
 
+	private static boolean noSingleInstance;
+
 	/**
 	 * Returns whether the XDG flag in the manifest (if any) is set to "true".
 	 * @return true if XDG directories are enabled, false otherwise
@@ -279,6 +281,15 @@ public class Options {
 					port = i;
 			}
 		},
+		NOSINGLEINSTANCE ("NoSingleInstance") {
+			@Override
+			public String write() { return noSingleInstance + ""; }
+
+			@Override
+			public void read(String s) {
+				noSingleInstance = !"false".equals(s);
+			}
+		},
 
 		// in-game options
 		SCREEN_RESOLUTION ("Screen Resolution", "ScreenResolution", "Restart (Ctrl+Shift+F5) to apply resolution changes.") {
@@ -1492,6 +1503,8 @@ public class Options {
 	 */
 	public static int getPort() { return port; }
 
+	public static boolean noSingleInstance() { return noSingleInstance; }
+
 	/**
 	 * Returns the cursor scale.
 	 * @return the scale [0.5, 2]