add shutdown hook to shutdown core on SIGTERM

core/src/main/groovy/com/muwire/core/Core.groovy

@@ -1,6 +1,7 @@
 package com.muwire.core
 
 import java.nio.charset.StandardCharsets
+import java.util.concurrent.atomic.AtomicBoolean
 
 import com.muwire.core.connection.ConnectionAcceptor
 import com.muwire.core.connection.ConnectionEstablisher
@@ -74,6 +75,8 @@ public class Core {
     private final DirectoryWatcher directoryWatcher
     final FileManager fileManager
     
+    private final AtomicBoolean shutdown = new AtomicBoolean()
+        
     public Core(MuWireSettings props, File home, String myVersion) {
         this.home = home		
         this.muOptions = props
@@ -241,6 +244,10 @@ public class Core {
     }
     
     public void shutdown() {
+        if (!shutdown.compareAndSet(false, true)) {
+            log.info("already shutting down")
+            return
+        }
         log.info("shutting down download manageer")
         downloadManager.shutdown()
         log.info("shutting down connection acceeptor")

gui/griffon-app/lifecycle/Ready.groovy

@@ -98,6 +98,9 @@ class Ready extends AbstractLifecycleHandler {
                 "Can't connect to I2P router", JOptionPane.WARNING_MESSAGE)
             System.exit(0)
         }
+        Runtime.getRuntime().addShutdownHook({
+            core.shutdown() 
+        })
         core.startServices()
         application.context.put("muwire-settings", props)
         application.context.put("core",core)