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/*
 * 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 scala.concurrent.ExecutionContext;

/**
 * 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();
		}
	}

	/**
	 * Return a direct execution context. The direct execution context executes the runnable directly
	 * in the calling thread.
	 *
	 * @return Direct execution context.
	 */
	public static ExecutionContext directExecutionContext() {
		return DirectExecutionContext.INSTANCE;
	}

	/**
	 * Direct execution context.
	 */
	private static class DirectExecutionContext implements ExecutionContext {

		static final DirectExecutionContext INSTANCE = new DirectExecutionContext();

		private DirectExecutionContext() {}

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

		@Override
		public void reportFailure(Throwable cause) {
			throw new IllegalStateException("Error in direct execution context.", cause);
		}

		@Override
		public ExecutionContext prepare() {
			return this;
		}
	}
}