/*
 * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package utils;

import java.lang.management.ManagementFactory;
import java.lang.management.MemoryPoolMXBean;
import java.lang.management.MemoryUsage;
import java.util.ArrayList;
import java.util.List;

/**
 * This is an class used to allocate specified amount of metaspace and heap.
 * Object of this class should be created before any garbage collection cycles because GC can
 * shrink heap and Runtime.maxMemory() might report unexpected value.
 */
public class GarbageProducer{

    // Uses fixed small objects to avoid Humongous objects allocation with G1 GC.
    public static final int MEMORY_CHUNK = 2048;

    public static List<Object> allocatedMetaspace;
    public static List<Object> allocatedMemory;

    private final Runtime runtime;
    private final float targetMemoryUsagePercent;
    private final long garbageToAllocate;

    /**
     * @param targetMemoryUsagePercent how many percent of metaspace and heap to allocate
     */
    public GarbageProducer(float targetMemoryUsagePercent) {
        this.targetMemoryUsagePercent = targetMemoryUsagePercent;
        runtime = Runtime.getRuntime();
        // Calculate amount of garbage to occupate targetMemoryUsagePercent of heap
        garbageToAllocate = runtime.freeMemory()
            - (long) ((1.0 - targetMemoryUsagePercent) * runtime.maxMemory());
    }

    /**
     * Allocates heap and metaspace upon exit targetMemoryUsagePercent percents
     * of heap and metaspace have been consumed.
     */
    public void allocateMetaspaceAndHeap() {
        // Metaspace should be filled before Java Heap to prevent unexpected OOME
        // in the Java Heap while filling Metaspace
        allocatedMetaspace = eatMetaspace(targetMemoryUsagePercent);
        allocatedMemory = allocateGarbage(garbageToAllocate);
    }

    private List<Object> eatMetaspace(float targetUsage) {
        List<Object> list = new ArrayList<>();
        final String metaspacePoolName = "Metaspace";
        MemoryPoolMXBean metaspacePool = null;
        for (MemoryPoolMXBean pool : ManagementFactory.getMemoryPoolMXBeans()) {
            if (pool.getName().contains(metaspacePoolName)) {
                metaspacePool = pool;
                break;
            }
        }
        if (metaspacePool == null) {
            throw new RuntimeException("MXBean for Metaspace pool wasn't found");
        }
        float currentUsage;
        GeneratedClassProducer gp = new GeneratedClassProducer();
        do {
            try {
                list.add(gp.create(0));
            } catch (OutOfMemoryError oome) {
                list = null;
                throw new RuntimeException("Unexpected OOME '" + oome.getMessage() + "' while eating " + targetUsage + " of Metaspace.");
            }
            MemoryUsage memoryUsage = metaspacePool.getUsage();
            currentUsage = (((float) memoryUsage.getUsed()) / memoryUsage.getMax());
        } while (currentUsage < targetUsage);
        return list;
    }

    private List<Object> allocateGarbage(long garbageToAllocate) {
        long allocated = 0l;
        List<Object> list = new ArrayList<>();
        do {
            try {
                list.add(new byte[MEMORY_CHUNK]);
                allocated += MEMORY_CHUNK;
            } catch (OutOfMemoryError e) {
                list = null;
                throw new RuntimeException("Unexpected OOME '" + e.getMessage() + "'. Allocated " + allocated + " bytes.");
            }
        } while (allocated < garbageToAllocate);
        return list;
    }
}