HadoopShutdownHookManager.java

/*
 * 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.ignite.internal.processors.hadoop.impl.v2;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Fake manager for shutdown hooks.
 */
public class HadoopShutdownHookManager {
    /** */
    private static final HadoopShutdownHookManager MGR = new HadoopShutdownHookManager();

    /**
     * Return <code>ShutdownHookManager</code> singleton.
     *
     * @return <code>ShutdownHookManager</code> singleton.
     */
    public static HadoopShutdownHookManager get() {
        return MGR;
    }

    /** */
    private Set<Runnable> hooks = Collections.synchronizedSet(new HashSet<Runnable>());

    /** */
    private AtomicBoolean shutdownInProgress = new AtomicBoolean(false);

    /**
     * Singleton.
     */
    private HadoopShutdownHookManager() {
        // No-op.
    }

    /**
     * Adds a shutdownHook with a priority, the higher the priority
     * the earlier will run. ShutdownHooks with same priority run
     * in a non-deterministic order.
     *
     * @param shutdownHook shutdownHook <code>Runnable</code>
     * @param priority priority of the shutdownHook.
     */
    public void addShutdownHook(Runnable shutdownHook, int priority) {
        if (shutdownHook == null)
            throw new IllegalArgumentException("shutdownHook cannot be NULL");

        hooks.add(shutdownHook);
    }

    /**
     * Removes a shutdownHook.
     *
     * @param shutdownHook shutdownHook to remove.
     * @return TRUE if the shutdownHook was registered and removed,
     * FALSE otherwise.
     */
    public boolean removeShutdownHook(Runnable shutdownHook) {
        return hooks.remove(shutdownHook);
    }

    /**
     * Indicates if a shutdownHook is registered or not.
     *
     * @param shutdownHook shutdownHook to check if registered.
     * @return TRUE/FALSE depending if the shutdownHook is is registered.
     */
    public boolean hasShutdownHook(Runnable shutdownHook) {
        return hooks.contains(shutdownHook);
    }

    /**
     * Indicates if shutdown is in progress or not.
     *
     * @return TRUE if the shutdown is in progress, otherwise FALSE.
     */
    public boolean isShutdownInProgress() {
        return shutdownInProgress.get();
    }
}