Handles uncaught errors (OutOfMemoryError, StackOverflowError etc) by freeing memory, showing an error message and force quit.

data/strings/FreeColMessages.properties

@@ -2789,6 +2789,7 @@ model.unit.hardyPioneer.noMoreTools=%location%: Your Hardy Pioneer has used up a
 # -10-- Client
 
 # main: main() and support in FreeCol.java
+error.seriousError=An error occurred that is forcing FreeCol to exit. Please refer to the log file for more information.
 error.couldNotFind=An error occurred because file %name% could not be found
 error.couldNotLoad=An error occurred while trying to load the game from file %name%
 error.couldNotLoadDifficulty=An error occurred while trying to load difficulty options from file %name%.

src/net/sf/freecol/client/FreeColClient.java

@@ -71,6 +71,9 @@ public final class FreeColClient {
 
     private static final Logger logger = Logger.getLogger(FreeColClient.class.getName());
 
+    @SuppressWarnings("unused")
+    private byte[] memoryToBeFreedOnOutOfMemory = new byte[10 * 1024 * 1024];
+    
     private final ConnectController connectController;
 
     private final PreGameController preGameController;
@@ -167,6 +170,7 @@ public final class FreeColClient {
         if (FreeCol.getHeadless() && savedGame == null && spec == null) {
             FreeCol.fatal(logger, Messages.message("client.headlessRequires"));
         }
+        
         mapEditor = false;
 
         // Look for base data directory and get base resources loaded.
@@ -246,6 +250,8 @@ public final class FreeColClient {
         // Initialize Sound (depends on client options)
         this.soundController = new SoundController(this, sound);
         
+        overrideDefaultUncaughtExceptionHandler();
+        
         /*
          * Please do NOT move preloading before mods are loaded -- as that
          * might cause some images to be loaded from base and other images
@@ -1010,4 +1016,31 @@ public final class FreeColClient {
         }
         FreeCol.quit(0);
     }
+    
+    private void overrideDefaultUncaughtExceptionHandler() {
+        // This overrides the handler in FreeCol:
+        Thread.setDefaultUncaughtExceptionHandler((Thread thread, Throwable e) -> {
+            // Free enough space to ensure we can perform the next operations.
+            if (e instanceof Error) {
+                memoryToBeFreedOnOutOfMemory = null;
+                gui.emergencyPurge();
+            }
+            
+            final boolean seriousError = (e instanceof Error);
+            try {
+                logger.log(Level.WARNING, "Uncaught exception from thread: " + thread, e);
+                
+                if (seriousError) {
+                    gui.showErrorPanel(Messages.message("error.seriousError"), () -> {
+                        System.exit(1);
+                    });
+                }
+            } catch (Throwable t) {
+                if (seriousError) {
+                    t.printStackTrace();
+                    System.exit(1);
+                }
+            }
+        });
+    }
 }

src/net/sf/freecol/client/gui/GUI.java

@@ -2506,4 +2506,14 @@ public class GUI extends FreeColClientHolder {
     public boolean canGameChangingModsBeAdded() {
         return true;
     }
+
+
+    /**
+     * A method to be called only on serious Errors in order
+     * to ensure sufficient memory for displaying an error
+     * message.
+     */
+    public void emergencyPurge() {
+
+    }
 }

src/net/sf/freecol/client/gui/SwingGUI.java

@@ -56,6 +56,7 @@ import net.sf.freecol.FreeCol;
 import net.sf.freecol.client.ClientOptions;
 import net.sf.freecol.client.FreeColClient;
 import net.sf.freecol.client.control.MapTransform;
+import net.sf.freecol.client.control.SoundController;
 import net.sf.freecol.client.gui.animation.Animation;
 import net.sf.freecol.client.gui.animation.Animations;
 // Special dialogs and panels
@@ -1373,6 +1374,18 @@ public class SwingGUI extends GUI {
         refresh();
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void emergencyPurge() {
+        imageCache.clear();
+        
+        final SoundController sc = getFreeColClient().getSoundController();
+        sc.setDefaultPlaylist(List.of());
+        sc.playMusic(null);
+    }
+
 
     // Highest level panel and dialog handling