/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.flink.runtime.iterative.concurrent;

import java.io.IOException;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

import org.apache.flink.core.memory.DataInputView;
import org.apache.flink.core.memory.DataOutputView;
import org.apache.flink.runtime.iterative.io.SerializedUpdateBuffer;

/**
 * A concurrent datastructure that establishes a backchannel buffer between an iteration head
 * and an iteration tail.
 */
public class BlockingBackChannel {

	/** buffer to send back the superstep results */
	private final SerializedUpdateBuffer buffer;

	/** a one element queue used for blocking hand over of the buffer */
	private final BlockingQueue<SerializedUpdateBuffer> queue;

	public BlockingBackChannel(SerializedUpdateBuffer buffer) {
		this.buffer = buffer;
		queue = new ArrayBlockingQueue<SerializedUpdateBuffer>(1);
	}

	/**
	 * Called by iteration head after it has sent all input for the current superstep through the data channel
	 * (blocks iteration head).
	 */
	public DataInputView getReadEndAfterSuperstepEnded() {
		try {
			return queue.take().switchBuffers();
		} catch (InterruptedException | IOException e) {
			throw new RuntimeException(e);
		}
	}

	/**
	 * Called by iteration tail to save the output of the current superstep.
	 */
	public DataOutputView getWriteEnd() {
		return buffer;
	}

	/**
	 * Called by iteration tail to signal that all input of a superstep has been processed
	 * (unblocks iteration head).
	 */
	public void notifyOfEndOfSuperstep() {
		queue.offer(buffer);
	}

}