shutdown() function for CleanerThread:

* de-initialize CleanerThread variables on thread shutdown
* don't run CleanerThread as daemon

Author: jjYBdx4IL

batik-util/src/main/java/org/apache/batik/util/CleanerThread.java

@@ -22,6 +22,8 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 import java.lang.ref.ReferenceQueue;
 import java.lang.ref.SoftReference;
 import java.lang.ref.WeakReference;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
 import java.lang.ref.PhantomReference;
 
 /**
@@ -34,15 +36,18 @@ Licensed to the Apache Software Foundation (ASF) under one or more
  */
 public class CleanerThread extends Thread {
 
-    static volatile ReferenceQueue queue = null;
+    static volatile ReferenceQueue<?> queue = null;
     static CleanerThread  thread = null;
+    /* latch to signal CleanerThread shutdown request */
+    private static CountDownLatch shutdownLatch = null;
 
-    public static ReferenceQueue getReferenceQueue() {
+    public static ReferenceQueue<?> getReferenceQueue() {
 
-        if ( queue == null ) {
-            synchronized (CleanerThread.class) {
-                queue = new ReferenceQueue();
+        synchronized (CleanerThread.class) {
+            if ( queue == null ) {
+                queue = new ReferenceQueue<>();
                 thread = new CleanerThread();
+                shutdownLatch = new CountDownLatch(1);
             }
         }
         return queue;
@@ -94,29 +99,42 @@ public PhantomReferenceCleared(Object o) {
 
     protected CleanerThread() {
         super("Batik CleanerThread");
-        setDaemon(true);
         start();
     }
 
+    @Override
     public void run() {
-        while(true) {
-            try {
-                Reference ref;
-                try {
-                    ref = queue.remove();
+        try {
+            while(!shutdownLatch.await(100, TimeUnit.SECONDS)) {
+                Reference<?> ref;
+                do {
+                    ref = queue.poll();
                     // System.err.println("Cleaned: " + ref);
-                } catch (InterruptedException ie) {
-                    continue;
-                }
-
-                if (ref instanceof ReferenceCleared) {
-                    ReferenceCleared rc = (ReferenceCleared)ref;
-                    rc.cleared();
-                }
-            } catch (ThreadDeath td) {
-                throw td;
-            } catch (Throwable t) {
-                t.printStackTrace();
+                    if (ref != null && ref instanceof ReferenceCleared) {
+                        ReferenceCleared rc = (ReferenceCleared)ref;
+                        rc.cleared();
+                    }
+                } while (ref != null);
+            }
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        } finally {
+            synchronized (CleanerThread.class) {
+                queue = null;
+                thread = null;
+                shutdownLatch = null;
+            }
+        }
+    }
+
+    /**
+     * Request CleanerThread shutdown and wait for it to finish.
+     */
+    public static void shutdown() throws InterruptedException {
+        synchronized (CleanerThread.class) {
+            if (shutdownLatch != null) {
+                shutdownLatch.countDown();
+                thread.join();
             }
         }
     }

batik-util/src/main/java/org/apache/batik/util/HaltingThread.java

@@ -31,7 +31,7 @@ public class HaltingThread extends Thread {
     /**
      * Boolean indicating if this thread has ever been 'halted'.
      */
-    protected boolean beenHalted = false;
+    protected volatile boolean beenHalted = false;
 
     public HaltingThread() { }