/*
 * Copyright (c) 2019, SAP SE. All rights reserved.
 * Copyright (c) 2019, 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
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#ifndef SHARE_MEMORY_METASPACE_CHUNKHEADERPOOL_HPP
#define SHARE_MEMORY_METASPACE_CHUNKHEADERPOOL_HPP

#include "memory/metaspace/internStat.hpp"
#include "memory/metaspace/metachunk.hpp"
#include "utilities/debug.hpp"
#include "utilities/globalDefinitions.hpp"

namespace metaspace {

// A simple helper class; A pool of unused chunk headers.

class ChunkHeaderPool {

  static const int slab_capacity = 128;

  struct slab_t {
    slab_t* next;
    int top;
    Metachunk elems [slab_capacity]; // var sized;
  };

  IntCounter _num_slabs;
  slab_t* _first_slab;
  slab_t* _current_slab;

  IntCounter _num_handed_out;

  MetachunkList _freelist;

  const bool _delete_on_destruction;

  void allocate_new_slab();

  static ChunkHeaderPool _chunkHeaderPool;


public:

  ChunkHeaderPool(bool delete_on_destruction);

  ~ChunkHeaderPool();

  // Allocates a Metachunk structure. The structure is uninitialized.
  Metachunk* allocate_chunk_header() {

    Metachunk* c = NULL;

    DEBUG_ONLY(verify(false));

    c = _freelist.remove_first();
    assert(c == NULL || c->is_dead(), "Not a freelist chunk header?");

    if (c == NULL) {

      if (_current_slab == NULL ||
          _current_slab->top == slab_capacity) {
        allocate_new_slab();
        assert(_current_slab->top < slab_capacity, "Sanity");
      }

      c = _current_slab->elems + _current_slab->top;
      _current_slab->top ++;

    }

    _num_handed_out.increment();

    // By contract, the returned structure is uninitialized.
    // Zap to make this clear.
    DEBUG_ONLY(c->zap_header(0xBB);)

    return c;

  }

  void return_chunk_header(Metachunk* c) {
    // We only ever should return free chunks, since returning chunks
    // happens only on merging and merging only works with free chunks.
    assert(c != NULL && c->is_free(), "Sanity");
#ifdef ASSERT
    // In debug, fill dead header with pattern.
    c->zap_header(0xCC);
    c->set_next(NULL);
    c->set_prev(NULL);
#endif
    c->set_dead();
    _freelist.add(c);
    _num_handed_out.decrement();

  }

  // Returns number of allocated elements.
  int used() const                   { return _num_handed_out.get(); }

  // Returns number of elements in free list.
  int freelist_size() const          { return _freelist.size(); }

  // Returns size of memory used.
  size_t memory_footprint_words() const;

  DEBUG_ONLY(void verify(bool slow) const;)

  // Returns reference to the one global chunk header pool.
  static ChunkHeaderPool& pool() { return _chunkHeaderPool; }

};


} // namespace metaspace




#endif // SHARE_MEMORY_METASPACE_CHUNKHEADERPOOL_HPP