/*
 * 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.concurrent;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.annotation.Nonnull;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.TimeUnit;

/**
 * Collection of {@link Executor} implementations
 */
public class Executors {

	private static final Logger LOG = LoggerFactory.getLogger(Executors.class);

	/**
	 * Return a direct executor. The direct executor directly executes the runnable in the calling
	 * thread.
	 *
	 * @return Direct executor
	 */
	public static Executor directExecutor() {
		return DirectExecutor.INSTANCE;
	}

	/**
	 * Direct executor implementation.
	 */
	private static class DirectExecutor implements Executor {

		static final DirectExecutor INSTANCE = new DirectExecutor();

		private DirectExecutor() {}

		@Override
		public void execute(@Nonnull Runnable command) {
			command.run();
		}
	}

	/**
	 * Gracefully shutdown the given {@link ExecutorService}. The call waits the given timeout that
	 * all ExecutorServices terminate. If the ExecutorServices do not terminate in this time,
	 * they will be shut down hard.
	 *
	 * @param timeout to wait for the termination of all ExecutorServices
	 * @param unit of the timeout
	 * @param executorServices to shut down
	 */
	public static void gracefulShutdown(long timeout, TimeUnit unit, ExecutorService... executorServices) {
		for (ExecutorService executorService: executorServices) {
			executorService.shutdown();
		}

		boolean wasInterrupted = false;
		final long endTime = unit.toMillis(timeout) + System.currentTimeMillis();
		long timeLeft = unit.toMillis(timeout);
		boolean hasTimeLeft = timeLeft > 0L;

		for (ExecutorService executorService: executorServices) {
			if (wasInterrupted || !hasTimeLeft) {
				executorService.shutdownNow();
			} else {
				try {
					if (!executorService.awaitTermination(timeLeft, TimeUnit.MILLISECONDS)) {
						LOG.warn("ExecutorService did not terminate in time. Shutting it down now.");
						executorService.shutdownNow();
					}
				} catch (InterruptedException e) {
					LOG.warn("Interrupted while shutting down executor services. Shutting all " +
						"remaining ExecutorServices down now.", e);
					executorService.shutdownNow();

					wasInterrupted = true;

					Thread.currentThread().interrupt();
				}

				timeLeft = endTime - System.currentTimeMillis();
				hasTimeLeft = timeLeft > 0L;
			}
		}
	}
}