/*
 * Copyright (c) 2017, Google 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 MyPackage;

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

/** API for handling the underlying heap sampling monitoring system. */
public class HeapMonitor {
  static {
    try {
      System.loadLibrary("HeapMonitor");
    } catch (UnsatisfiedLinkError ule) {
      System.err.println("Could not load HeapMonitor library");
      System.err.println("java.library.path: " + System.getProperty("java.library.path"));
      throw ule;
    }
  }

  private static volatile int arrays[][];

  /** Enable heap monitoring sampling given a rate and maximum garbage to keep in memory. */
  public native static void enableSampling(int rate, int maximumGarbage);

  /** Enable heap monitoring sampling given a rate. */
  public static void enableSampling(int rate) {
    enableSampling(rate, 200);
  }

  /** Enable heap monitoring sampling with default values for rate and maximum garbage. */
  public static void enableSampling() {
    enableSampling(1 << 19);
  }

  public native static void disableSampling();
  public native static boolean areSamplingStatisticsZero();
  public native static boolean statsHaveExpectedNumberSamples(int expected, int percentError);

  /** Do the frames provided exist in live, recent garbage, and frequent garbage. */
  public native static boolean framesExistEverywhere(Frame[] frames);
  /** Do the frames provided not exist in live, recent garbage, and frequent garbage. */
  public native static boolean framesExistNowhere(Frame[] frames);

  /**
   * Allocate memory but first create a stack trace of a particular depth.
   *
   * @return list of frames for the allocation.
   */
  public static List<Frame> allocate(int depth) {
    List<Frame> frames = new ArrayList<Frame>();
    if (depth > 1) {
      createStackDepth(depth - 1, frames);
      frames.add(new Frame("allocate", "(I)Ljava/util/List;", "HeapMonitor.java", 73));
    } else {
      actuallyAllocate(frames);
      frames.add(new Frame("actuallyAllocate", "(Ljava/util/List;)I", "HeapMonitor.java", 127));
      frames.add(new Frame("allocate", "(I)Ljava/util/List;", "HeapMonitor.java", 76));
    }
    return frames;
  }

  /**
   * Allocate memory but first create a stack trace.
   *
   * @return list of frames for the allocation.
   */
  public static List<Frame> allocate() {
    int sum = 0;
    List<Frame> frames = new ArrayList<Frame>();
    allocate(frames);
    frames.add(new Frame("allocate", "()Ljava/util/List;", "HeapMonitor.java", 91));
    return frames;
  }

  private static void createStackDepth(int depth, List<Frame> frames) {
    if (depth > 1) {
      createStackDepth(depth - 1, frames);
      frames.add(new Frame("createStackDepth", "(ILjava/util/List;)V", "HeapMonitor.java", 98));
    } else {
      allocate(frames);
      frames.add(new Frame("createStackDepth", "(ILjava/util/List;)V", "HeapMonitor.java", 101));
    }
  }

  private static void allocate(List<Frame> frames) {
    int sum = 0;
    for (int j = 0; j < 1000; j++) {
      sum += actuallyAllocate(frames);
    }
    frames.add(new Frame("actuallyAllocate", "(Ljava/util/List;)I", "HeapMonitor.java", 127));
    frames.add(new Frame("allocate", "(Ljava/util/List;)V", "HeapMonitor.java", 109));
  }

  private static int actuallyAllocate(List<Frame> frames) {
    int sum = 0;

    // Let us assume that a 1-element array is 24 bytes of memory and we want
    // 2MB allocated.
    int iterations = (1 << 19) / 6;

    if (arrays == null) {
      arrays = new int[iterations][];
    }

    for (int i = 0; i < iterations; i++) {
      int tmp[] = new int[1];
      // Force it to be kept and, at the same time, wipe out any previous data.
      arrays[i] = tmp;
      sum += arrays[0][0];
    }
    return sum;
  }

  /** Remove the reference to the global array to free data at the next GC. */
  public static void freeStorage() {
    arrays = null;
  }
}