/*

 * Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved.

 * Copyright (c) 2018, 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.

 *

 */

#ifndef SHARE_RUNTIME_THREADHEAPSAMPLER_HPP

#define SHARE_RUNTIME_THREADHEAPSAMPLER_HPP

#include "memory/allocation.hpp"

class ThreadHeapSampler {

 private:

  // Statics for the fast log

  static const int FastLogNumBits = 10;

  static const int FastLogMask = (1 << FastLogNumBits) - 1;

  size_t _bytes_until_sample;

  // Cheap random number generator

  static uint64_t _rnd;

  static bool _log_table_initialized;

  static double _log_table[1<<FastLogNumBits];  // Constant

  static volatile int _sampling_interval;

  void pick_next_geometric_sample();

  void pick_next_sample(size_t overflowed_bytes = 0);

  static double fast_log2(const double& d);

  static bool init_log_table();

  uint64_t next_random(uint64_t rnd);

 public:

  ThreadHeapSampler() : _bytes_until_sample(0) {

    _rnd = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(this));

    if (_rnd == 0) {

      _rnd = 1;

    }

  }

  size_t bytes_until_sample()                    { return _bytes_until_sample;   }

  void set_bytes_until_sample(size_t bytes)      { _bytes_until_sample = bytes;  }

  void check_for_sampling(oop obj, size_t size_in_bytes, size_t bytes_allocated_before);

  static void set_sampling_interval(int sampling_interval);

  static int get_sampling_interval();

};

#endif // SHARE_RUNTIME_THREADHEAPSAMPLER_HPP