Issue 5790 - Get ready for integration into Chromium

libadblockplus-android-settings/src/org/adblockplus/libadblockplus/android/settings/AdblockHelper.java

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 221 matching lines @@
   public int getCounter()
   {
     return referenceCounter.get();
   }
 
   /**
    * Register AdblockHelper engine client
    * @param asynchronous If `true` engines will be created in background thread without locking of
    *                     current thread. Use waitForReady() before getEngine() later.
    *                     If `false` locks current thread.
+   * @return if a new instance is allocated
    */
-  public synchronized void retain(boolean asynchronous)
+  public synchronized boolean retain(boolean asynchronous)
   {
+    boolean firstInstance = false;
+
     if (referenceCounter.getAndIncrement() == 0)
     {
+      firstInstance = true;
+
       if (!asynchronous)
       {
         createAdblock();
       }
       else
       {
         // latch is required for async (see `waitForReady()`)
         engineCreated = new CountDownLatch(1);
 
         new Thread(new Runnable()
         {
           @Override
           public void run()
           {
             createAdblock();
 
             // unlock waiting client thread
             engineCreated.countDown();
           }
         }).start();
       }
     }
+    return firstInstance;
   }
 
   /**
    * Unregister AdblockHelper engine client
+   * @return `true` if the last instance is destroyed
    */
-  public synchronized void release()
+  public synchronized boolean release()
   {
+    boolean lastInstance = false;
+
     if (referenceCounter.decrementAndGet() == 0)
     {
+      lastInstance = true;
+
       if (engineCreated != null)
       {
         // retained asynchronously
         waitForReady();
         disposeAdblock();
 
         // to unlock waiting client in waitForReady()
         engineCreated.countDown();
         engineCreated = null;
       }
       else
       {
         disposeAdblock();
       }
     }
+    return lastInstance;
   }
 }