/* Copyright (C) 2013-2022 TU Dortmund
 * This file is part of LearnLib, http://www.learnlib.de/.
 *
 * Licensed 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 de.learnlib.api.oracle.parallelism;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * A markup interface for a component that manages a pool of threads that may want to be shut down after usage.
 *
 * @author Malte Isberner
 * @author frohme
 * @see ExecutorService
 */
public interface ThreadPool {

    /**
     * Shuts down all worker threads, but waits for any queued queries to be processed.
     *
     * @see ExecutorService#shutdown()
     */
    void shutdown();

    /**
     * Shuts down all worker threads, and attempts to abort any query processing currently taking place.
     *
     * @see ExecutorService#shutdownNow()
     */
    void shutdownNow();

    /**
     * The policy for dealing with thread pools.
     *
     * @author Malte Isberner
     */
    enum PoolPolicy {
        /**
         * Maintain a fixed thread pool. The threads will be started immediately, and will terminate only if {@link
         * ThreadPool#shutdown()} or {@link ThreadPool#shutdownNow()} are called.
         *
         * @see Executors#newFixedThreadPool(int)
         */
        FIXED,
        /**
         * Maintain a "cached" thread pool. Threads will be created on-demand, but will be kept alive for re-use when
         * all jobs are processed. However, they will be terminated when they have been idle for 60 seconds.
         * <p>
         * Note that as opposed to {@link Executors#newCachedThreadPool()}, the specified pool size will never be
         * exceeded.
         *
         * @see Executors#newCachedThreadPool()
         */
        CACHED
    }
}
