//
   //  ========================================================================
   //  Copyright (c) 1995-2014 Mort Bay Consulting Pty. Ltd.
   //  ------------------------------------------------------------------------
   //  All rights reserved. This program and the accompanying materials
   //  are made available under the terms of the Eclipse Public License v1.0
   //  and Apache License v2.0 which accompanies this distribution.
   //
   //      The Eclipse Public License is available at
  //      http://www.eclipse.org/legal/epl-v10.html
  //
  //      The Apache License v2.0 is available at
  //      http://www.opensource.org/licenses/apache2.0.php
  //
  //  You may elect to redistribute this code under either of these licenses.
  //  ========================================================================
  //
  
  package org.eclipse.jetty.util;
  
  import java.io.IOException;
  import java.io.InterruptedIOException;
  import java.util.concurrent.CancellationException;
  import java.util.concurrent.CountDownLatch;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.eclipse.jetty.util.log.Log;
  import org.eclipse.jetty.util.log.Logger;
  import org.eclipse.jetty.util.thread.NonBlockingThread;
  
  /* ------------------------------------------------------------ */
  /**
   * An implementation of Callback that blocks until success or failure.
   */
  public class BlockingCallback implements Callback
  {
      private static final Logger LOG = Log.getLogger(BlockingCallback.class);
      
      private static Throwable SUCCEEDED=new Throwable()
      {
          @Override
          public String toString() { return "SUCCEEDED"; }
      };
      
      private final CountDownLatch _latch = new CountDownLatch(1);
      private final AtomicReference<Throwable> _state = new AtomicReference<>();
      
      public BlockingCallback()
      {}
  
      @Override
      public void succeeded()
      {
          if (_state.compareAndSet(null,SUCCEEDED))
              _latch.countDown();
      }
  
      @Override
      public void failed(Throwable cause)
      {
          if (_state.compareAndSet(null,cause))
              _latch.countDown();
      }
  
      /** Block until the Callback has succeeded or failed and 
       * after the return leave in the state to allow reuse.
       * This is useful for code that wants to repeatable use a FutureCallback to convert
       * an asynchronous API to a blocking API. 
       * @throws IOException if exception was caught during blocking, or callback was cancelled 
       */
      public void block() throws IOException
      {
          if (NonBlockingThread.isNonBlockingThread())
              LOG.warn("Blocking a NonBlockingThread: ",new Throwable());
          
          try
          {
              _latch.await();
              Throwable state=_state.get();
              if (state==SUCCEEDED)
                  return;
              if (state instanceof IOException)
                  throw (IOException) state;
              if (state instanceof CancellationException)
                  throw (CancellationException) state;
              throw new IOException(state);
          }
          catch (final InterruptedException e)
          {
              throw new InterruptedIOException(){{initCause(e);}};
          }
          finally
          {
              _state.set(null);
          }
      }
      
      
      @Override
     public String toString()
     {
         return String.format("%s@%x{%s}",BlockingCallback.class.getSimpleName(),hashCode(),_state.get());
     }
 
 }