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 /*

  * Copyright (c) 2013, 2015, 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.

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  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP

 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP

 #include "gc_implementation/g1/g1_globals.hpp"

 #include "gc_implementation/g1/g1CardCounts.hpp"

 #include "memory/allocation.hpp"

 #include "runtime/safepoint.hpp"

 #include "runtime/thread.inline.hpp"

 #include "utilities/globalDefinitions.hpp"

 class DirtyCardQueue;

 class G1CollectedHeap;

 class G1RemSet;

 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;

   int               _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;

   bool default_use_cache() const {

     return (G1ConcRSLogCacheSize > 0);

   }

  public:

   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(uint worker_i, G1RemSet* g1rs, DirtyCardQueue* into_cset_dcq);

   // 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 entire committed heap

   void reset_card_counts();

   // 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_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP