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The Netty project is an effort to provide an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.

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/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project 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.jboss.netty.util.internal;

import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.TimeUnit;

/**
 * Shuts down a list of {@link Executor}s.  {@link #terminate(Executor...)} will
 * shut down all specified {@link ExecutorService}s immediately and wait for
 * their termination.  An {@link Executor} which is not an {@link ExecutorService}
 * will be ignored silently.
 */
public final class ExecutorUtil {

    /**
     * Try to call {@link ExecutorService#shutdownNow()}
     */
    public static void shutdownNow(Executor executor) {
        if (executor instanceof ExecutorService) {
            ExecutorService es = (ExecutorService) executor;
            try {
                es.shutdownNow();
            } catch (SecurityException ex) {
                // Running in a restricted environment - fall back.
                try {
                    es.shutdown();
                } catch (SecurityException ex2) {
                    // Running in a more restricted environment.
                    // Can't shut down this executor - skip to the next.
                } catch (NullPointerException ex2) {
                    // Some JDK throws NPE here, but shouldn't.
                }
            } catch (NullPointerException ex) {
                // Some JDK throws NPE here, but shouldn't.
            }
        }
    }

    /**
     * Returns {@code true} if and only if the specified {@code executor}
     * is an {@link ExecutorService} and is shut down.  Please note that this
     * method returns {@code false} if the specified {@code executor} is not an
     * {@link ExecutorService}.
     */
    public static boolean isShutdown(Executor executor) {
        if (executor instanceof ExecutorService) {
            if (((ExecutorService) executor).isShutdown()) {
                return true;
            }
        }
        return false;
    }

    /**
     * Shuts down the specified executors.
     */
    public static void terminate(Executor... executors) {
        terminate(DeadLockProofWorker.PARENT, executors);
    }
    /**
     * Shuts down the specified executors using the given {@link ThreadLocal} to check if there is a deadlock
     */
    public static void terminate(ThreadLocal deadLockChecker, Executor... executors) {
        // Check nulls.
        if (executors == null) {
            throw new NullPointerException("executors");
        }

        Executor[] executorsCopy = new Executor[executors.length];
        for (int i = 0; i < executors.length; i ++) {
            if (executors[i] == null) {
                throw new NullPointerException("executors[" + i + ']');
            }
            executorsCopy[i] = executors[i];
        }

        // Check dead lock.
        final Executor currentParent = deadLockChecker.get();
        if (currentParent != null) {
            for (Executor e: executorsCopy) {
                if (e == currentParent) {
                    throw new IllegalStateException(
                            "An Executor cannot be shut down from the thread " +
                            "acquired from itself.  Please make sure you are " +
                            "not calling releaseExternalResources() from an " +
                            "I/O worker thread.");
                }
            }
        }

        // Shut down all executors.
        boolean interrupted = false;
        for (Executor e: executorsCopy) {
            if (!(e instanceof ExecutorService)) {
                continue;
            }

            ExecutorService es = (ExecutorService) e;
            for (;;) {
                shutdownNow(es);

                try {
                    if (es.awaitTermination(100, TimeUnit.MILLISECONDS)) {
                        break;
                    }
                } catch (InterruptedException ex) {
                    interrupted = true;
                }
            }
        }

        if (interrupted) {
            Thread.currentThread().interrupt();
        }
    }

    private ExecutorUtil() {
    }
}