Issue 6274 - ANR on cancelling elemhide thread for load error

libadblockplus-android-webview/src/org/adblockplus/libadblockplus/android/webview/AdblockWebView.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 955 matching lines @@
         AdblockEngine.generateAppInfo(this.getContext(), debugMode),
         this.getContext().getDir(AdblockEngine.BASE_PATH_DIRECTORY, Context.MODE_PRIVATE).getAbsolutePath())
       .enableElementHiding(true)
       .build();
   }
 
   private class ElemHideThread extends Thread
   {
     private String selectorsString;
     private CountDownLatch finishedLatch;
+    private AtomicBoolean isFinished;
     private AtomicBoolean isCancelled;
 
     public ElemHideThread(CountDownLatch finishedLatch)
     {
       this.finishedLatch = finishedLatch;
+      isFinished = new AtomicBoolean(false);
       isCancelled = new AtomicBoolean(false);
     }
 
     @Override
     public void run()
     {
       try
       {
         if (adblockEngine == null)
         {
@@ skipping 55 matching lines @@
       {
         if (finishedRunnable != null)
         {
           finishedRunnable.run();
         }
       }
     }
 
     private void finish(String result)
     {
+      isFinished.set(true);
       d("Setting elemhide string " + result.length() + " bytes");
       elemHideSelectorsString = result;
       onFinished();
     }
 
     private final Object finishedRunnableLockObject = new Object();
     private Runnable finishedRunnable;
 
     public void setFinishedRunnable(Runnable runnable)
     {
       synchronized (finishedRunnableLockObject)
       {
         this.finishedRunnable = runnable;
       }
     }
 
     public void cancel()
     {
       w("Cancelling elemhide thread " + this);
-      isCancelled.set(true);
-
-      finish(EMPTY_ELEMHIDE_ARRAY_STRING);
+      if (!isFinished.get())

[jens, 2018/01/17 08:28:43]

To make the if statement more readable, I would probably reverse the logic.

[anton, 2018/01/17 08:33:55]

Done. See patch set #2

+      {
+        isCancelled.set(true);
+        finish(EMPTY_ELEMHIDE_ARRAY_STRING);
+      }
+      else
+      {
+        w("This thread is finished, exiting silently " + this);
+      }
     }
   }
 
   private Runnable elemHideThreadFinishedRunnable = new Runnable()
   {
     @Override
     public void run()
     {
       synchronized (elemHideThreadLockObject)
       {
@@ skipping 348 matching lines @@
         w("Busy with elemhide selectors, delayed disposing scheduled");
         elemHideThread.setFinishedRunnable(disposeRunnable);
       }
       else
       {
         disposeRunnable.run();
       }
     }
   }
 }