/*

 * 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

 * or visit www.oracle.com if you need additional information or have any

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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