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/*
 * Copyright (c) 2008-2019 The Aspectran Project
 *
 * 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 com.aspectran.core.util.thread;

import com.aspectran.core.util.logging.Log;
import com.aspectran.core.util.logging.LogFactory;

import java.util.ArrayList;
import java.util.List;
import java.util.ListIterator;

/**
 * Manages the shutdown-hook thread and tasks to execute on shutdown.
 *
 * @since 4.0.0
 */
public class ShutdownHooks {

    private static final Log log = LogFactory.getLog(ShutdownHooks.class);

    private static final List tasks = new ArrayList<>();

    private static Thread hook;

    public static synchronized  T add(final T task) {
        if (task == null) {
            throw new IllegalArgumentException("task must not be null");
        }

        if (hook == null) {
            hook = addHook(new Thread("goodbye") {
                @Override
                public void run() {
                    runTasks();
                }
            });
        }

        if (log.isDebugEnabled()) {
            log.debug("Adding shutdown-hook task: " + task);
        }

        tasks.add(task);
        return task;
    }

    public static synchronized void remove(final Task task) {
        if (task == null) {
            throw new IllegalArgumentException("task must not be null");
        }

        // ignore if hook never installed
        if (hook == null) {
            return;
        }

        // Drop the task
        tasks.remove(task);

        // If there are no more tasks, then remove the hook thread
        if (tasks.isEmpty()) {
            removeHook(hook);
            hook = null;
        }
    }

    private static Thread addHook(final Thread thread) {
        if (log.isDebugEnabled()) {
            log.debug("Registering shutdown-hook: " + thread);
        }
        try {
            Runtime.getRuntime().addShutdownHook(thread);
        } catch (AbstractMethodError e) {
            // JDK 1.3+ only method. Bummer.
            if (log.isTraceEnabled()) {
                log.trace("Failed to register shutdown-hook: " + e);
            }
        }
        return thread;
    }

    private static void removeHook(final Thread thread) {
        if (log.isDebugEnabled()) {
            log.debug("Removing shutdown-hook: " + thread);
        }

        try {
            Runtime.getRuntime().removeShutdownHook(thread);
        } catch (AbstractMethodError e) {
            // JDK 1.3+ only method. Bummer.
            if (log.isTraceEnabled()) {
                log.trace("Failed to register shutdown-hook: " + e);
            }
        } catch (IllegalStateException e) {
            // The VM is shutting down, not a big deal; ignore
        }
    }

    private static synchronized void runTasks() {
        if (log.isDebugEnabled()) {
            log.debug("Running all shutdown-hook tasks");
        }

        List list = new ArrayList<>(tasks);
        for (ListIterator iter = list.listIterator(list.size()); iter.hasPrevious();) {
            Task task = iter.previous();
            if (log.isDebugEnabled()) {
                log.debug("Running task: " + task);
            }
            try {
                task.run();
            } catch (Throwable e) {
                log.warn("Task failed", e);
            }
        }

        tasks.clear();
    }

    /**
     * Essentially a {@link Runnable} which allows running to throw an exception.
     */
    public interface Task {

        void run() throws Exception;

    }

}