WalletAppKit/Template: Cleaner way to check if the app is already running. Backport from Lighthouse.

core/src/main/java/com/google/bitcoin/kits/WalletAppKit.java

@@ -30,12 +30,10 @@ import com.google.common.util.concurrent.Service;
 import com.subgraph.orchid.TorClient;
 import org.bitcoinj.wallet.Protos;
 
-import java.io.File;
+import java.io.*;
-import java.io.FileInputStream;
-import java.io.IOException;
-import java.io.InputStream;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
+import java.nio.channels.FileLock;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
@@ -188,6 +186,29 @@ public class WalletAppKit extends AbstractIdleService {
      */
     protected void onSetupCompleted() { }
 
+    /**
+     * Tests to see if the spvchain file has an operating system file lock on it. Useful for checking if your app
+     * is already running. If another copy of your app is running and you start the appkit anyway, an exception will
+     * be thrown during the startup process. Returns false if the chain file does not exist.
+     */
+    public boolean isChainFileLocked() throws IOException {
+        RandomAccessFile file2 = null;
+        try {
+            File file = new File(directory, filePrefix + ".spvchain");
+            if (!file.exists())
+                return false;
+            file2 = new RandomAccessFile(file, "rw");
+            FileLock lock = file2.getChannel().tryLock();
+            if (lock == null)
+                return true;
+            lock.close();
+            return false;
+        } finally {
+            if (file2 != null)
+                file2.close();
+        }
+    }
+
     @Override
     protected void startUp() throws Exception {
         // Runs in a separate thread.

wallettemplate/src/main/java/wallettemplate/Main.java

@@ -5,10 +5,8 @@ import com.google.bitcoin.core.NetworkParameters;
 import com.google.bitcoin.kits.WalletAppKit;
 import com.google.bitcoin.params.MainNetParams;
 import com.google.bitcoin.params.RegTestParams;
-import com.google.bitcoin.store.BlockStoreException;
 import com.google.bitcoin.utils.BriefLogFormatter;
 import com.google.bitcoin.utils.Threading;
-import com.google.common.base.Throwables;
 import javafx.application.Application;
 import javafx.application.Platform;
 import javafx.fxml.FXMLLoader;
@@ -41,22 +39,12 @@ public class Main extends Application {
         instance = this;
         // Show the crash dialog for any exceptions that we don't handle and that hit the main loop.
         GuiUtils.handleCrashesOnThisThread();
-        try {
-            init(mainWindow);
-        } catch (Throwable t) {
-            // Nicer message for the case where the block store file is locked.
-            if (Throwables.getRootCause(t) instanceof BlockStoreException) {
-                GuiUtils.informationalAlert("Already running", "This application is already running and cannot be started twice.");
-            } else {
-                throw t;
-            }
-        }
-    }
 
-    private void init(Stage mainWindow) throws IOException {
+        // Match Aqua UI style.
         if (System.getProperty("os.name").toLowerCase().contains("mac")) {
             AquaFx.style();
         }
+
         // Load the GUI. The Controller class will be automagically created and wired up.
         URL location = getClass().getResource("main.fxml");
         FXMLLoader loader = new FXMLLoader(location);
@@ -78,6 +66,16 @@ public class Main extends Application {
         Threading.USER_THREAD = Platform::runLater;
         // Create the app kit. It won't do any heavyweight initialization until after we start it.
         bitcoin = new WalletAppKit(params, new File("."), APP_NAME);
+        if (bitcoin.isChainFileLocked()) {
+            informationalAlert("Already running", "This application is already running and cannot be started twice.");
+            Platform.exit();
+            return;
+        }
+
+        mainWindow.show();
+
+        // Now configure and start the appkit. This will take a second or two - we could show a temporary splash screen
+        // or progress widget to keep the user engaged whilst we initialise, but we don't.
         if (params == RegTestParams.get()) {
             bitcoin.connectToLocalHost();   // You should run a regtest mode bitcoind locally.
         } else if (params == MainNetParams.get()) {
@@ -89,9 +87,6 @@ public class Main extends Application {
             // As an example!
             // bitcoin.useTor();
         }
-
-        // Now configure and start the appkit. This will take a second or two - we could show a temporary splash screen
-        // or progress widget to keep the user engaged whilst we initialise, but we don't.
         bitcoin.setDownloadListener(controller.progressBarUpdater())
                .setBlockingStartup(false)
                .setUserAgent(APP_NAME, "1.0");
@@ -102,7 +97,6 @@ public class Main extends Application {
         bitcoin.peerGroup().setMaxConnections(11);
         System.out.println(bitcoin.wallet());
         controller.onBitcoinSetup();
-        mainWindow.show();
     }
 
     public class OverlayUI<T> {