/*

 * Copyright (c) 2013, 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

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 */

#ifndef SHARE_VM_GC_G1_G1HOTCARDCACHE_HPP

#define SHARE_VM_GC_G1_G1HOTCARDCACHE_HPP

#include "gc/g1/g1CardCounts.hpp"

#include "gc/g1/g1_globals.hpp"

#include "memory/allocation.hpp"

#include "runtime/safepoint.hpp"

#include "runtime/thread.hpp"

#include "utilities/globalDefinitions.hpp"

class CardTableEntryClosure;

class DirtyCardQueue;

class G1CollectedHeap;

class HeapRegion;

// An evicting cache of cards that have been logged by the G1 post

// write barrier. Placing a card in the cache delays the refinement

// of the card until the card is evicted, or the cache is drained

// during the next evacuation pause.

//

// The first thing the G1 post write barrier does is to check whether

// the card containing the updated pointer is already dirty and, if

// so, skips the remaining code in the barrier.

//

// Delaying the refinement of a card will make the card fail the

// first is_dirty check in the write barrier, skipping the remainder

// of the write barrier.

//

// This can significantly reduce the overhead of the write barrier

// code, increasing throughput.

class G1HotCardCache: public CHeapObj<mtGC> {

  G1CollectedHeap*  _g1h;

  bool              _use_cache;

  G1CardCounts      _card_counts;

  // The card cache table

  jbyte**           _hot_cache;

  size_t            _hot_cache_size;

  size_t            _hot_cache_par_chunk_size;

  // Avoids false sharing when concurrently updating _hot_cache_idx or

  // _hot_cache_par_claimed_idx. These are never updated at the same time

  // thus it's not necessary to separate them as well

  char _pad_before[DEFAULT_CACHE_LINE_SIZE];

  volatile size_t _hot_cache_idx;

  volatile size_t _hot_cache_par_claimed_idx;

  char _pad_after[DEFAULT_CACHE_LINE_SIZE];

  // The number of cached cards a thread claims when flushing the cache

  static const int ClaimChunkSize = 32;

 public:

  static bool default_use_cache() {

    return (G1ConcRSLogCacheSize > 0);

  }

  G1HotCardCache(G1CollectedHeap* g1h);

  ~G1HotCardCache();

  void initialize(G1RegionToSpaceMapper* card_counts_storage);

  bool use_cache() { return _use_cache; }

  void set_use_cache(bool b) {

    _use_cache = (b ? default_use_cache() : false);

  }

  // Returns the card to be refined or NULL.

  //

  // Increments the count for given the card. if the card is not 'hot',

  // it is returned for immediate refining. Otherwise the card is

  // added to the hot card cache.

  // If there is enough room in the hot card cache for the card we're

  // adding, NULL is returned and no further action in needed.

  // If we evict a card from the cache to make room for the new card,

  // the evicted card is then returned for refinement.

  jbyte* insert(jbyte* card_ptr);

  // Refine the cards that have delayed as a result of

  // being in the cache.

  void drain(CardTableEntryClosure* cl, uint worker_i);

  // Set up for parallel processing of the cards in the hot cache

  void reset_hot_cache_claimed_index() {

    _hot_cache_par_claimed_idx = 0;

  }

  // Resets the hot card cache and discards the entries.

  void reset_hot_cache() {

    assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint");

    assert(Thread::current()->is_VM_thread(), "Current thread should be the VMthread");

    if (default_use_cache()) {

        reset_hot_cache_internal();

    }

  }

  // Zeros the values in the card counts table for the given region

  void reset_card_counts(HeapRegion* hr);

 private:

  void reset_hot_cache_internal() {

    assert(_hot_cache != NULL, "Logic");

    _hot_cache_idx = 0;

    for (size_t i = 0; i < _hot_cache_size; i++) {

      _hot_cache[i] = NULL;

    }

  }

};

#endif // SHARE_VM_GC_G1_G1HOTCARDCACHE_HPP