/*
 * 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.io.network.api;

import static org.apache.flink.util.Preconditions.checkNotNull;

import java.io.IOException;

import org.apache.flink.core.memory.DataInputView;
import org.apache.flink.core.memory.DataOutputView;
import org.apache.flink.runtime.checkpoint.CheckpointOptions;
import org.apache.flink.runtime.event.RuntimeEvent;

/**
 * Checkpoint barriers are used to align checkpoints throughout the streaming topology. The
 * barriers are emitted by the sources when instructed to do so by the JobManager. When
 * operators receive a CheckpointBarrier on one of its inputs, it knows that this is the point 
 * between the pre-checkpoint and post-checkpoint data.
 * 
 * <p>Once an operator has received a checkpoint barrier from all its input channels, it
 * knows that a certain checkpoint is complete. It can trigger the operator specific checkpoint
 * behavior and broadcast the barrier to downstream operators.
 * 
 * <p>Depending on the semantic guarantees, may hold off post-checkpoint data until the checkpoint
 * is complete (exactly once).
 * 
 * <p>The checkpoint barrier IDs are strictly monotonous increasing.
 */
public class CheckpointBarrier extends RuntimeEvent {

	private final long id;
	private final long timestamp;
	private final CheckpointOptions checkpointOptions;

	public CheckpointBarrier(long id, long timestamp, CheckpointOptions checkpointOptions) {
		this.id = id;
		this.timestamp = timestamp;
		this.checkpointOptions = checkNotNull(checkpointOptions);
	}

	public long getId() {
		return id;
	}

	public long getTimestamp() {
		return timestamp;
	}

	public CheckpointOptions getCheckpointOptions() {
		return checkpointOptions;
	}

	// ------------------------------------------------------------------------
	// Serialization
	// ------------------------------------------------------------------------

	//
	//  These methods are inherited form the generic serialization of AbstractEvent
	//  but would require the CheckpointBarrier to be mutable. Since all serialization
	//  for events goes through the EventSerializer class, which has special serialization
	//  for the CheckpointBarrier, we don't need these methods
	// 

	@Override
	public void write(DataOutputView out) throws IOException {
		throw new UnsupportedOperationException("This method should never be called");
	}

	@Override
	public void read(DataInputView in) throws IOException {
		throw new UnsupportedOperationException("This method should never be called");
	}

	// ------------------------------------------------------------------------

	@Override
	public int hashCode() {
		return (int) (id ^ (id >>> 32) ^ timestamp ^ (timestamp >>> 32));
	}

	@Override
	public boolean equals(Object other) {
		if (other == this) {
			return true;
		}
		else if (other == null || other.getClass() != CheckpointBarrier.class) {
			return false;
		}
		else {
			CheckpointBarrier that = (CheckpointBarrier) other;
			return that.id == this.id && that.timestamp == this.timestamp &&
					this.checkpointOptions.equals(that.checkpointOptions);
		}
	}

	@Override
	public String toString() {
		return String.format("CheckpointBarrier %d @ %d Options: %s", id, timestamp, checkpointOptions);
	}
}