/*
 * 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.api.common;

import org.apache.flink.annotation.Public;

/**
 * The execution mode specifies how a batch program is executed in terms
 * of data exchange: pipelining or batched.
 */
@Public
public enum ExecutionMode {

	/**
	 * Executes the program in a pipelined fashion (including shuffles and broadcasts),
	 * except for data exchanges that are susceptible to deadlocks when pipelining.
	 * These data exchanges are performed in a batch manner.
	 *
	 * An example of situations that are susceptible to deadlocks (when executed in a
	 * pipelined manner) are data flows that branch (one data set consumed by multiple
	 * operations) and re-join later:
	 * <pre>{@code
	 * DataSet data = ...;
	 * DataSet mapped1 = data.map(new MyMapper());
	 * DataSet mapped2 = data.map(new AnotherMapper());
	 * mapped1.join(mapped2).where(...).equalTo(...);
	 * }</pre>
	 */
	PIPELINED,

	/**
	 * Executes the program in a pipelined fashion (including shuffles and broadcasts),
	 * <strong>including</strong> data exchanges that are susceptible to deadlocks when
	 * executed via pipelining.
	 *
	 * Usually, {@link #PIPELINED} is the preferable option, which pipelines most
	 * data exchanges and only uses batch data exchanges in situations that are
	 * susceptible to deadlocks.
	 *
	 * This option should only be used with care and only in situations where the
	 * programmer is sure that the program is safe for full pipelining and that
	 * Flink was too conservative when choosing the batch exchange at a certain
	 * point.
	 */
	PIPELINED_FORCED,

//	This is for later, we are missing a bit of infrastructure for this.
//	/**
//	 * The execution mode starts executing the program in a pipelined fashion
//	 * (except for deadlock prone situations), similar to the {@link #PIPELINED}
//	 * option. In the case of a task failure, re-execution happens in a batched
//	 * mode, as defined for the {@link #BATCH} option.
//	 */
//	PIPELINED_WITH_BATCH_FALLBACK,

	/**
	 * This mode executes all shuffles and broadcasts in a batch fashion, while
	 * pipelining data between operations that exchange data only locally
	 * between one producer and one consumer.
	 */
	BATCH,

	/**
	 * This mode executes the program in a strict batch way, including all points
	 * where data is forwarded locally from one producer to one consumer. This mode
	 * is typically more expensive to execute than the {@link #BATCH} mode. It does
	 * guarantee that no successive operations are ever executed concurrently.
	 */
	BATCH_FORCED
}