AsyncEventIOHandler.java

/*
   Copyright (c) 2015 LinkedIn Corp.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package com.linkedin.r2.transport.http.server;

import com.linkedin.r2.message.stream.entitystream.ReadHandle;

import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletOutputStream;
import java.io.IOException;

/**
 * This IO handler works with Servlet 3.0 async API (but with synchronous IO).
 *
 * @author Zhenkai Zhu
 */
public class AsyncEventIOHandler extends SyncIOHandler
{
  private final AbstractAsyncR2StreamServlet.WrappedAsyncContext _ctx;
  private volatile boolean _responseWriteStarted = false;
  private boolean _inLoop = false;

  public AsyncEventIOHandler(ServletInputStream is, ServletOutputStream os, AbstractAsyncR2StreamServlet.WrappedAsyncContext ctx, int bufferCapacity)
  {
    super(is, os, bufferCapacity, Integer.MAX_VALUE);
    _ctx = ctx;
  }

  @Override
  protected boolean shouldContinue()
  {
    boolean shouldContinue =  !requestReadFinished()
        || (_responseWriteStarted && !responseWriteFinished());

    if (!shouldContinue)
    {
      synchronized (this)
      {
        // check again in synchronized block to make sure we can exit safely
        shouldContinue =  !requestReadFinished()
            || (_responseWriteStarted && !responseWriteFinished());

        if (!shouldContinue)
        {
          _inLoop = false;
        }
      }
    }
    return shouldContinue;
  }

  public void exitLoop()
  {
    super.exitLoop();
  }

  @Override
  public void onInit(ReadHandle rh)
  {
    synchronized (this)
    {
      _responseWriteStarted = true;
    }
    super.onInit(rh);
  }

  @Override
  public void loop() throws ServletException, IOException
  {
    synchronized (this)
    {
      if (_inLoop)
      {
        return;
      }
      else
      {
        _inLoop = true;
      }
    }
    super.loop();
    if (requestReadFinished() && responseWriteFinished())
    {
      _ctx.complete();
    }
  }
}