com.cloudera.oryx.common.lang.JVMUtils.java Source code

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Here is the source code for com.cloudera.oryx.common.lang.JVMUtils.java

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/*
 * Copyright (c) 2014, Cloudera, Inc. All Rights Reserved.
 *
 * Cloudera, Inc. 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
 *
 * This software 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.cloudera.oryx.common.lang;

import java.io.Closeable;
import java.util.Deque;
import java.util.LinkedList;

import com.google.common.base.Preconditions;

import com.cloudera.oryx.common.io.IOUtils;

/**
 * JVM-related utility methods.
 */
public final class JVMUtils {

    private static final Deque<Closeable> closeAtShutdown = new LinkedList<>();

    private JVMUtils() {
    }

    /**
     * Adds a shutdown hook that try to call {@link Closeable#close()} on the given argument
     * at JVM shutdown.
     *
     * @param closeable thing to close
     */
    public static void closeAtShutdown(Closeable closeable) {
        Preconditions.checkNotNull(closeable);
        synchronized (closeAtShutdown) {
            if (closeAtShutdown.isEmpty()) {
                Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
                    @Override
                    public void run() {
                        synchronized (closeAtShutdown) {
                            for (Closeable c : closeAtShutdown) {
                                IOUtils.closeQuietly(c);
                            }
                        }
                    }
                }));
            }
            closeAtShutdown.push(closeable);
        }
    }

    /**
     * @return approximate heap used, in bytes
     */
    public static long getUsedMemory() {
        Runtime runtime = Runtime.getRuntime();
        return runtime.totalMemory() - runtime.freeMemory();
    }

}