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 /*

  * Copyright (c) 2001, 2014, 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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  */

 #include "precompiled.hpp"

 #include "gc_implementation/g1/concurrentG1Refine.hpp"

 #include "gc_implementation/g1/concurrentG1RefineThread.hpp"

 #include "gc_implementation/g1/g1BlockOffsetTable.inline.hpp"

 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"

 #include "gc_implementation/g1/g1CollectorPolicy.hpp"

 #include "gc_implementation/g1/g1HotCardCache.hpp"

 #include "gc_implementation/g1/g1GCPhaseTimes.hpp"

 #include "gc_implementation/g1/g1OopClosures.inline.hpp"

 #include "gc_implementation/g1/g1RemSet.inline.hpp"

 #include "gc_implementation/g1/heapRegionManager.inline.hpp"

 #include "gc_implementation/g1/heapRegionRemSet.hpp"

 #include "memory/iterator.hpp"

 #include "oops/oop.inline.hpp"

 #include "utilities/intHisto.hpp"

 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC

 #define CARD_REPEAT_HISTO 0

 #if CARD_REPEAT_HISTO

 static size_t ct_freq_sz;

 static jbyte* ct_freq = NULL;

 void init_ct_freq_table(size_t heap_sz_bytes) {

   if (ct_freq == NULL) {

     ct_freq_sz = heap_sz_bytes/CardTableModRefBS::card_size;

     ct_freq = new jbyte[ct_freq_sz];

     for (size_t j = 0; j < ct_freq_sz; j++) ct_freq[j] = 0;

   }

 }

 void ct_freq_note_card(size_t index) {

   assert(0 <= index && index < ct_freq_sz, "Bounds error.");

   if (ct_freq[index] < 100) { ct_freq[index]++; }

 }

 static IntHistogram card_repeat_count(10, 10);

 void ct_freq_update_histo_and_reset() {

   for (size_t j = 0; j < ct_freq_sz; j++) {

     card_repeat_count.add_entry(ct_freq[j]);

     ct_freq[j] = 0;

   }

 }

 #endif

 G1RemSet::G1RemSet(G1CollectedHeap* g1, CardTableModRefBS* ct_bs)

   : _g1(g1), _conc_refine_cards(0),

     _ct_bs(ct_bs), _g1p(_g1->g1_policy()),

     _cg1r(g1->concurrent_g1_refine()),

     _cset_rs_update_cl(NULL),

     _cards_scanned(NULL), _total_cards_scanned(0),

     _prev_period_summary()

 {

   _seq_task = new SubTasksDone(NumSeqTasks);

   guarantee(n_workers() > 0, "There should be some workers");

   _cset_rs_update_cl = NEW_C_HEAP_ARRAY(OopsInHeapRegionClosure*, n_workers(), mtGC);

   for (uint i = 0; i < n_workers(); i++) {

     _cset_rs_update_cl[i] = NULL;

   }

   if (G1SummarizeRSetStats) {

     _prev_period_summary.initialize(this);

   }

 }

 G1RemSet::~G1RemSet() {

   delete _seq_task;

   for (uint i = 0; i < n_workers(); i++) {

     assert(_cset_rs_update_cl[i] == NULL, "it should be");

   }

   FREE_C_HEAP_ARRAY(OopsInHeapRegionClosure*, _cset_rs_update_cl, mtGC);

 }

 void CountNonCleanMemRegionClosure::do_MemRegion(MemRegion mr) {

   if (_g1->is_in_g1_reserved(mr.start())) {

     _n += (int) ((mr.byte_size() / CardTableModRefBS::card_size));

     if (_start_first == NULL) _start_first = mr.start();

   }

 }

 class ScanRSClosure : public HeapRegionClosure {

   size_t _cards_done, _cards;

   G1CollectedHeap* _g1h;

   OopsInHeapRegionClosure* _oc;

   CodeBlobToOopClosure* _code_root_cl;

   G1BlockOffsetSharedArray* _bot_shared;

   G1SATBCardTableModRefBS *_ct_bs;

   double _strong_code_root_scan_time_sec;

   uint   _worker_i;

   int    _block_size;

   bool   _try_claimed;

 public:

   ScanRSClosure(OopsInHeapRegionClosure* oc,

                 CodeBlobToOopClosure* code_root_cl,

                 uint worker_i) :

     _oc(oc),

     _code_root_cl(code_root_cl),

     _strong_code_root_scan_time_sec(0.0),

     _cards(0),

     _cards_done(0),

     _worker_i(worker_i),

     _try_claimed(false)

   {

     _g1h = G1CollectedHeap::heap();

     _bot_shared = _g1h->bot_shared();

     _ct_bs = _g1h->g1_barrier_set();

     _block_size = MAX2<int>(G1RSetScanBlockSize, 1);

   }

   void set_try_claimed() { _try_claimed = true; }

   void scanCard(size_t index, HeapRegion *r) {

     // Stack allocate the DirtyCardToOopClosure instance

     HeapRegionDCTOC cl(_g1h, r, _oc,

                        CardTableModRefBS::Precise,

                        HeapRegionDCTOC::IntoCSFilterKind);

     // Set the "from" region in the closure.

     _oc->set_region(r);

     HeapWord* card_start = _bot_shared->address_for_index(index);

     HeapWord* card_end = card_start + G1BlockOffsetSharedArray::N_words;

     Space *sp = SharedHeap::heap()->space_containing(card_start);

     MemRegion sm_region = sp->used_region_at_save_marks();

     MemRegion mr = sm_region.intersection(MemRegion(card_start,card_end));

     if (!mr.is_empty() && !_ct_bs->is_card_claimed(index)) {

       // We make the card as "claimed" lazily (so races are possible

       // but they're benign), which reduces the number of duplicate

       // scans (the rsets of the regions in the cset can intersect).

       _ct_bs->set_card_claimed(index);

       _cards_done++;

       cl.do_MemRegion(mr);

     }

   }

   void printCard(HeapRegion* card_region, size_t card_index,

                  HeapWord* card_start) {

     gclog_or_tty->print_cr("T " UINT32_FORMAT " Region [" PTR_FORMAT ", " PTR_FORMAT ") "

                            "RS names card %p: "

                            "[" PTR_FORMAT ", " PTR_FORMAT ")",

                            _worker_i,

                            card_region->bottom(), card_region->end(),

                            card_index,

                            card_start, card_start + G1BlockOffsetSharedArray::N_words);

   }

   void scan_strong_code_roots(HeapRegion* r) {

     double scan_start = os::elapsedTime();

     r->strong_code_roots_do(_code_root_cl);

     _strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start);

   }

   bool doHeapRegion(HeapRegion* r) {

     assert(r->in_collection_set(), "should only be called on elements of CS.");

     HeapRegionRemSet* hrrs = r->rem_set();

     if (hrrs->iter_is_complete()) return false; // All done.

     if (!_try_claimed && !hrrs->claim_iter()) return false;

     // If we ever free the collection set concurrently, we should also

     // clear the card table concurrently therefore we won't need to

     // add regions of the collection set to the dirty cards region.

     _g1h->push_dirty_cards_region(r);

     // If we didn't return above, then

     //   _try_claimed || r->claim_iter()

     // is true: either we're supposed to work on claimed-but-not-complete

     // regions, or we successfully claimed the region.

     HeapRegionRemSetIterator iter(hrrs);

     size_t card_index;

     // We claim cards in block so as to recude the contention. The block size is determined by

     // the G1RSetScanBlockSize parameter.

     size_t jump_to_card = hrrs->iter_claimed_next(_block_size);

     for (size_t current_card = 0; iter.has_next(card_index); current_card++) {

       if (current_card >= jump_to_card + _block_size) {

         jump_to_card = hrrs->iter_claimed_next(_block_size);

       }

       if (current_card < jump_to_card) continue;

       HeapWord* card_start = _g1h->bot_shared()->address_for_index(card_index);

 #if 0

       gclog_or_tty->print("Rem set iteration yielded card [" PTR_FORMAT ", " PTR_FORMAT ").\n",

                           card_start, card_start + CardTableModRefBS::card_size_in_words);

 #endif

       HeapRegion* card_region = _g1h->heap_region_containing(card_start);

       _cards++;

       if (!card_region->is_on_dirty_cards_region_list()) {

         _g1h->push_dirty_cards_region(card_region);

       }

       // If the card is dirty, then we will scan it during updateRS.

       if (!card_region->in_collection_set() &&

           !_ct_bs->is_card_dirty(card_index)) {

         scanCard(card_index, card_region);

       }

     }

     if (!_try_claimed) {

       // Scan the strong code root list attached to the current region

       scan_strong_code_roots(r);

       hrrs->set_iter_complete();

     }

     return false;

   }

   double strong_code_root_scan_time_sec() {

     return _strong_code_root_scan_time_sec;

   }

   size_t cards_done() { return _cards_done;}

   size_t cards_looked_up() { return _cards;}

 };

 void G1RemSet::scanRS(OopsInHeapRegionClosure* oc,

                       CodeBlobToOopClosure* code_root_cl,

                       uint worker_i) {

   double rs_time_start = os::elapsedTime();

   HeapRegion *startRegion = _g1->start_cset_region_for_worker(worker_i);

   ScanRSClosure scanRScl(oc, code_root_cl, worker_i);

   _g1->collection_set_iterate_from(startRegion, &scanRScl);

   scanRScl.set_try_claimed();

   _g1->collection_set_iterate_from(startRegion, &scanRScl);

   double scan_rs_time_sec = (os::elapsedTime() - rs_time_start)

                             - scanRScl.strong_code_root_scan_time_sec();

   assert(_cards_scanned != NULL, "invariant");

   _cards_scanned[worker_i] = scanRScl.cards_done();

   _g1p->phase_times()->record_scan_rs_time(worker_i, scan_rs_time_sec * 1000.0);

   _g1p->phase_times()->record_strong_code_root_scan_time(worker_i,

                                                          scanRScl.strong_code_root_scan_time_sec() * 1000.0);

 }

 // Closure used for updating RSets and recording references that

 // point into the collection set. Only called during an

 // evacuation pause.

 class RefineRecordRefsIntoCSCardTableEntryClosure: public CardTableEntryClosure {

   G1RemSet* _g1rs;

   DirtyCardQueue* _into_cset_dcq;

 public:

   RefineRecordRefsIntoCSCardTableEntryClosure(G1CollectedHeap* g1h,

                                               DirtyCardQueue* into_cset_dcq) :

     _g1rs(g1h->g1_rem_set()), _into_cset_dcq(into_cset_dcq)

   {}

   bool do_card_ptr(jbyte* card_ptr, uint worker_i) {

     // The only time we care about recording cards that

     // contain references that point into the collection set

     // is during RSet updating within an evacuation pause.

     // In this case worker_i should be the id of a GC worker thread.

     assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");

     assert(worker_i < (ParallelGCThreads == 0 ? 1 : ParallelGCThreads), "should be a GC worker");

     if (_g1rs->refine_card(card_ptr, worker_i, true)) {

       // 'card_ptr' contains references that point into the collection

       // set. We need to record the card in the DCQS

       // (G1CollectedHeap::into_cset_dirty_card_queue_set())

       // that's used for that purpose.

       //

       // Enqueue the card

       _into_cset_dcq->enqueue(card_ptr);

     }

     return true;

   }

 };

 void G1RemSet::updateRS(DirtyCardQueue* into_cset_dcq, uint worker_i) {

   double start = os::elapsedTime();

   // Apply the given closure to all remaining log entries.

   RefineRecordRefsIntoCSCardTableEntryClosure into_cset_update_rs_cl(_g1, into_cset_dcq);

   _g1->iterate_dirty_card_closure(&into_cset_update_rs_cl, into_cset_dcq, false, worker_i);

   // Now there should be no dirty cards.

   if (G1RSLogCheckCardTable) {

     CountNonCleanMemRegionClosure cl(_g1);

     _ct_bs->mod_card_iterate(&cl);

     // XXX This isn't true any more: keeping cards of young regions

     // marked dirty broke it.  Need some reasonable fix.

     guarantee(cl.n() == 0, "Card table should be clean.");

   }

   _g1p->phase_times()->record_update_rs_time(worker_i, (os::elapsedTime() - start) * 1000.0);

 }

 void G1RemSet::cleanupHRRS() {

   HeapRegionRemSet::cleanup();

 }

 void G1RemSet::oops_into_collection_set_do(OopsInHeapRegionClosure* oc,

                                            CodeBlobToOopClosure* code_root_cl,

                                            uint worker_i) {

 #if CARD_REPEAT_HISTO

   ct_freq_update_histo_and_reset();

 #endif

   // We cache the value of 'oc' closure into the appropriate slot in the

   // _cset_rs_update_cl for this worker

   assert(worker_i < n_workers(), "sanity");

   _cset_rs_update_cl[worker_i] = oc;

   // A DirtyCardQueue that is used to hold cards containing references

   // that point into the collection set. This DCQ is associated with a

   // special DirtyCardQueueSet (see g1CollectedHeap.hpp).  Under normal

   // circumstances (i.e. the pause successfully completes), these cards

   // are just discarded (there's no need to update the RSets of regions

   // that were in the collection set - after the pause these regions

   // are wholly 'free' of live objects. In the event of an evacuation

   // failure the cards/buffers in this queue set are:

   // * passed to the DirtyCardQueueSet that is used to manage deferred

   //   RSet updates, or

   // * scanned for references that point into the collection set

   //   and the RSet of the corresponding region in the collection set

   //   is updated immediately.

   DirtyCardQueue into_cset_dcq(&_g1->into_cset_dirty_card_queue_set());

   assert((ParallelGCThreads > 0) || worker_i == 0, "invariant");

   // The two flags below were introduced temporarily to serialize

   // the updating and scanning of remembered sets. There are some

   // race conditions when these two operations are done in parallel

   // and they are causing failures. When we resolve said race

   // conditions, we'll revert back to parallel remembered set

   // updating and scanning. See CRs 6677707 and 6677708.

   if (G1UseParallelRSetUpdating || (worker_i == 0)) {

     updateRS(&into_cset_dcq, worker_i);

   } else {

     _g1p->phase_times()->record_update_rs_processed_buffers(worker_i, 0);

     _g1p->phase_times()->record_update_rs_time(worker_i, 0.0);

   }

   if (G1UseParallelRSetScanning || (worker_i == 0)) {

     scanRS(oc, code_root_cl, worker_i);

   } else {

     _g1p->phase_times()->record_scan_rs_time(worker_i, 0.0);

   }

   // We now clear the cached values of _cset_rs_update_cl for this worker

   _cset_rs_update_cl[worker_i] = NULL;

 }

 void G1RemSet::prepare_for_oops_into_collection_set_do() {

   cleanupHRRS();

   ConcurrentG1Refine* cg1r = _g1->concurrent_g1_refine();

   _g1->set_refine_cte_cl_concurrency(false);

   DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();

   dcqs.concatenate_logs();

   guarantee( _cards_scanned == NULL, "invariant" );

   _cards_scanned = NEW_C_HEAP_ARRAY(size_t, n_workers(), mtGC);

   for (uint i = 0; i < n_workers(); ++i) {

     _cards_scanned[i] = 0;

   }

   _total_cards_scanned = 0;

 }

 // This closure, applied to a DirtyCardQueueSet, is used to immediately

 // update the RSets for the regions in the CSet. For each card it iterates

 // through the oops which coincide with that card. It scans the reference

 // fields in each oop; when it finds an oop that points into the collection

 // set, the RSet for the region containing the referenced object is updated.

 class UpdateRSetCardTableEntryIntoCSetClosure: public CardTableEntryClosure {

   G1CollectedHeap* _g1;

   CardTableModRefBS* _ct_bs;

 public:

   UpdateRSetCardTableEntryIntoCSetClosure(G1CollectedHeap* g1,

                                           CardTableModRefBS* bs):

     _g1(g1), _ct_bs(bs)

   { }

   bool do_card_ptr(jbyte* card_ptr, uint worker_i) {

     // Construct the region representing the card.

     HeapWord* start = _ct_bs->addr_for(card_ptr);

     // And find the region containing it.

     HeapRegion* r = _g1->heap_region_containing(start);

     // Scan oops in the card looking for references into the collection set

     // Don't use addr_for(card_ptr + 1) which can ask for

     // a card beyond the heap.  This is not safe without a perm

     // gen.

     HeapWord* end   = start + CardTableModRefBS::card_size_in_words;

     MemRegion scanRegion(start, end);

     UpdateRSetImmediate update_rs_cl(_g1->g1_rem_set());

     FilterIntoCSClosure update_rs_cset_oop_cl(NULL, _g1, &update_rs_cl);

     FilterOutOfRegionClosure filter_then_update_rs_cset_oop_cl(r, &update_rs_cset_oop_cl);

     // We can pass false as the "filter_young" parameter here as:

     // * we should be in a STW pause,

     // * the DCQS to which this closure is applied is used to hold

     //   references that point into the collection set from the prior

     //   RSet updating,

     // * the post-write barrier shouldn't be logging updates to young

     //   regions (but there is a situation where this can happen - see

     //   the comment in G1RemSet::refine_card() below -

     //   that should not be applicable here), and

     // * during actual RSet updating, the filtering of cards in young

     //   regions in HeapRegion::oops_on_card_seq_iterate_careful is

     //   employed.

     // As a result, when this closure is applied to "refs into cset"

     // DCQS, we shouldn't see any cards in young regions.

     update_rs_cl.set_region(r);

     HeapWord* stop_point =

       r->oops_on_card_seq_iterate_careful(scanRegion,

                                           &filter_then_update_rs_cset_oop_cl,

                                           false /* filter_young */,

                                           NULL  /* card_ptr */);

     // Since this is performed in the event of an evacuation failure, we

     // we shouldn't see a non-null stop point

     assert(stop_point == NULL, "saw an unallocated region");

     return true;

   }

 };

 void G1RemSet::cleanup_after_oops_into_collection_set_do() {

   guarantee( _cards_scanned != NULL, "invariant" );

   _total_cards_scanned = 0;

   for (uint i = 0; i < n_workers(); ++i) {

     _total_cards_scanned += _cards_scanned[i];

   }

   FREE_C_HEAP_ARRAY(size_t, _cards_scanned, mtGC);

   _cards_scanned = NULL;

   // Cleanup after copy

   _g1->set_refine_cte_cl_concurrency(true);

   // Set all cards back to clean.

   _g1->cleanUpCardTable();

   DirtyCardQueueSet& into_cset_dcqs = _g1->into_cset_dirty_card_queue_set();

   int into_cset_n_buffers = into_cset_dcqs.completed_buffers_num();

   if (_g1->evacuation_failed()) {

     double restore_remembered_set_start = os::elapsedTime();

     // Restore remembered sets for the regions pointing into the collection set.

     if (G1DeferredRSUpdate) {

       // If deferred RS updates are enabled then we just need to transfer

       // the completed buffers from (a) the DirtyCardQueueSet used to hold

       // cards that contain references that point into the collection set

       // to (b) the DCQS used to hold the deferred RS updates

       _g1->dirty_card_queue_set().merge_bufferlists(&into_cset_dcqs);

     } else {

       CardTableModRefBS* bs = (CardTableModRefBS*)_g1->barrier_set();

       UpdateRSetCardTableEntryIntoCSetClosure update_rs_cset_immediate(_g1, bs);

       int n_completed_buffers = 0;

       while (into_cset_dcqs.apply_closure_to_completed_buffer(&update_rs_cset_immediate,

                                                     0, 0, true)) {

         n_completed_buffers++;

       }

       assert(n_completed_buffers == into_cset_n_buffers, "missed some buffers");

     }

     _g1->g1_policy()->phase_times()->record_evac_fail_restore_remsets((os::elapsedTime() - restore_remembered_set_start) * 1000.0);

   }

   // Free any completed buffers in the DirtyCardQueueSet used to hold cards

   // which contain references that point into the collection.

   _g1->into_cset_dirty_card_queue_set().clear();

   assert(_g1->into_cset_dirty_card_queue_set().completed_buffers_num() == 0,

          "all buffers should be freed");

   _g1->into_cset_dirty_card_queue_set().clear_n_completed_buffers();

 }

 class ScrubRSClosure: public HeapRegionClosure {

   G1CollectedHeap* _g1h;

   BitMap* _region_bm;

   BitMap* _card_bm;

   CardTableModRefBS* _ctbs;

 public:

   ScrubRSClosure(BitMap* region_bm, BitMap* card_bm) :

     _g1h(G1CollectedHeap::heap()),

     _region_bm(region_bm), _card_bm(card_bm),

     _ctbs(_g1h->g1_barrier_set()) {}

   bool doHeapRegion(HeapRegion* r) {

     if (!r->continuesHumongous()) {

       r->rem_set()->scrub(_ctbs, _region_bm, _card_bm);

     }

     return false;

   }

 };

 void G1RemSet::scrub(BitMap* region_bm, BitMap* card_bm) {

   ScrubRSClosure scrub_cl(region_bm, card_bm);

   _g1->heap_region_iterate(&scrub_cl);

 }

 void G1RemSet::scrub_par(BitMap* region_bm, BitMap* card_bm,

                                 uint worker_num, int claim_val) {

   ScrubRSClosure scrub_cl(region_bm, card_bm);

   _g1->heap_region_par_iterate_chunked(&scrub_cl,

                                        worker_num,

                                        n_workers(),

                                        claim_val);

 }

 G1TriggerClosure::G1TriggerClosure() :

   _triggered(false) { }

 G1InvokeIfNotTriggeredClosure::G1InvokeIfNotTriggeredClosure(G1TriggerClosure* t_cl,

                                                              OopClosure* oop_cl)  :

   _trigger_cl(t_cl), _oop_cl(oop_cl) { }

 G1Mux2Closure::G1Mux2Closure(OopClosure *c1, OopClosure *c2) :

   _c1(c1), _c2(c2) { }

 G1UpdateRSOrPushRefOopClosure::

 G1UpdateRSOrPushRefOopClosure(G1CollectedHeap* g1h,

                               G1RemSet* rs,

                               OopsInHeapRegionClosure* push_ref_cl,

                               bool record_refs_into_cset,

                               uint worker_i) :

   _g1(g1h), _g1_rem_set(rs), _from(NULL),

   _record_refs_into_cset(record_refs_into_cset),

   _push_ref_cl(push_ref_cl), _worker_i(worker_i) { }

 // Returns true if the given card contains references that point

 // into the collection set, if we're checking for such references;

 // false otherwise.

 bool G1RemSet::refine_card(jbyte* card_ptr, uint worker_i,

                            bool check_for_refs_into_cset) {

   assert(_g1->is_in_exact(_ct_bs->addr_for(card_ptr)),

          err_msg("Card at "PTR_FORMAT" index "SIZE_FORMAT" representing heap at "PTR_FORMAT" (%u) must be in committed heap",

                  p2i(card_ptr),

                  _ct_bs->index_for(_ct_bs->addr_for(card_ptr)),

                  _ct_bs->addr_for(card_ptr),

                  _g1->addr_to_region(_ct_bs->addr_for(card_ptr))));

   // If the card is no longer dirty, nothing to do.

   if (*card_ptr != CardTableModRefBS::dirty_card_val()) {

     // No need to return that this card contains refs that point

     // into the collection set.

     return false;

   }

   // Construct the region representing the card.

   HeapWord* start = _ct_bs->addr_for(card_ptr);

   // And find the region containing it.

   HeapRegion* r = _g1->heap_region_containing(start);

   // Why do we have to check here whether a card is on a young region,

   // given that we dirty young regions and, as a result, the

   // post-barrier is supposed to filter them out and never to enqueue

   // them? When we allocate a new region as the "allocation region" we

   // actually dirty its cards after we release the lock, since card

   // dirtying while holding the lock was a performance bottleneck. So,

   // as a result, it is possible for other threads to actually

   // allocate objects in the region (after the acquire the lock)

   // before all the cards on the region are dirtied. This is unlikely,

   // and it doesn't happen often, but it can happen. So, the extra

   // check below filters out those cards.

   if (r->is_young()) {

     return false;

   }

   // While we are processing RSet buffers during the collection, we

   // actually don't want to scan any cards on the collection set,

   // since we don't want to update remebered sets with entries that

   // point into the collection set, given that live objects from the

   // collection set are about to move and such entries will be stale

   // very soon. This change also deals with a reliability issue which

   // involves scanning a card in the collection set and coming across

   // an array that was being chunked and looking malformed. Note,

   // however, that if evacuation fails, we have to scan any objects

   // that were not moved and create any missing entries.

   if (r->in_collection_set()) {

     return false;

   }

   // The result from the hot card cache insert call is either:

   //   * pointer to the current card

   //     (implying that the current card is not 'hot'),

   //   * null

   //     (meaning we had inserted the card ptr into the "hot" card cache,

   //     which had some headroom),

   //   * a pointer to a "hot" card that was evicted from the "hot" cache.

   //

   G1HotCardCache* hot_card_cache = _cg1r->hot_card_cache();

   if (hot_card_cache->use_cache()) {

     assert(!check_for_refs_into_cset, "sanity");

     assert(!SafepointSynchronize::is_at_safepoint(), "sanity");

     card_ptr = hot_card_cache->insert(card_ptr);

     if (card_ptr == NULL) {

       // There was no eviction. Nothing to do.

       return false;

     }

     start = _ct_bs->addr_for(card_ptr);

     r = _g1->heap_region_containing(start);

     // Checking whether the region we got back from the cache

     // is young here is inappropriate. The region could have been

     // freed, reallocated and tagged as young while in the cache.

     // Hence we could see its young type change at any time.

   }

   // Don't use addr_for(card_ptr + 1) which can ask for

   // a card beyond the heap.  This is not safe without a perm

   // gen at the upper end of the heap.

   HeapWord* end   = start + CardTableModRefBS::card_size_in_words;

   MemRegion dirtyRegion(start, end);

 #if CARD_REPEAT_HISTO

   init_ct_freq_table(_g1->max_capacity());

   ct_freq_note_card(_ct_bs->index_for(start));

 #endif

   OopsInHeapRegionClosure* oops_in_heap_closure = NULL;

   if (check_for_refs_into_cset) {

     // ConcurrentG1RefineThreads have worker numbers larger than what

     // _cset_rs_update_cl[] is set up to handle. But those threads should

     // only be active outside of a collection which means that when they

     // reach here they should have check_for_refs_into_cset == false.

     assert((size_t)worker_i < n_workers(), "index of worker larger than _cset_rs_update_cl[].length");

     oops_in_heap_closure = _cset_rs_update_cl[worker_i];

   }

   G1UpdateRSOrPushRefOopClosure update_rs_oop_cl(_g1,

                                                  _g1->g1_rem_set(),

                                                  oops_in_heap_closure,

                                                  check_for_refs_into_cset,

                                                  worker_i);

   update_rs_oop_cl.set_from(r);

   G1TriggerClosure trigger_cl;

   FilterIntoCSClosure into_cs_cl(NULL, _g1, &trigger_cl);

   G1InvokeIfNotTriggeredClosure invoke_cl(&trigger_cl, &into_cs_cl);

   G1Mux2Closure mux(&invoke_cl, &update_rs_oop_cl);

   FilterOutOfRegionClosure filter_then_update_rs_oop_cl(r,

                         (check_for_refs_into_cset ?

                                 (OopClosure*)&mux :

                                 (OopClosure*)&update_rs_oop_cl));

   // The region for the current card may be a young region. The

   // current card may have been a card that was evicted from the

   // card cache. When the card was inserted into the cache, we had

   // determined that its region was non-young. While in the cache,

   // the region may have been freed during a cleanup pause, reallocated

   // and tagged as young.

   //

   // We wish to filter out cards for such a region but the current

   // thread, if we're running concurrently, may "see" the young type

   // change at any time (so an earlier "is_young" check may pass or

   // fail arbitrarily). We tell the iteration code to perform this

   // filtering when it has been determined that there has been an actual

   // allocation in this region and making it safe to check the young type.

   bool filter_young = true;

   HeapWord* stop_point =

     r->oops_on_card_seq_iterate_careful(dirtyRegion,

                                         &filter_then_update_rs_oop_cl,

                                         filter_young,

                                         card_ptr);

   // If stop_point is non-null, then we encountered an unallocated region

   // (perhaps the unfilled portion of a TLAB.)  For now, we'll dirty the

   // card and re-enqueue: if we put off the card until a GC pause, then the

   // unallocated portion will be filled in.  Alternatively, we might try

   // the full complexity of the technique used in "regular" precleaning.

   if (stop_point != NULL) {

     // The card might have gotten re-dirtied and re-enqueued while we

     // worked.  (In fact, it's pretty likely.)

     if (*card_ptr != CardTableModRefBS::dirty_card_val()) {

       *card_ptr = CardTableModRefBS::dirty_card_val();

       MutexLockerEx x(Shared_DirtyCardQ_lock,

                       Mutex::_no_safepoint_check_flag);

       DirtyCardQueue* sdcq =

         JavaThread::dirty_card_queue_set().shared_dirty_card_queue();

       sdcq->enqueue(card_ptr);

     }

   } else {

     _conc_refine_cards++;

   }

   // This gets set to true if the card being refined has

   // references that point into the collection set.

   bool has_refs_into_cset = trigger_cl.triggered();

   // We should only be detecting that the card contains references

   // that point into the collection set if the current thread is

   // a GC worker thread.

   assert(!has_refs_into_cset || SafepointSynchronize::is_at_safepoint(),

            "invalid result at non safepoint");

   return has_refs_into_cset;

 }

 void G1RemSet::print_periodic_summary_info(const char* header) {

   G1RemSetSummary current;

   current.initialize(this);

   _prev_period_summary.subtract_from(&current);

   print_summary_info(&_prev_period_summary, header);

   _prev_period_summary.set(&current);

 }

 void G1RemSet::print_summary_info() {

   G1RemSetSummary current;

   current.initialize(this);

   print_summary_info(&current, " Cumulative RS summary");

 }

 void G1RemSet::print_summary_info(G1RemSetSummary * summary, const char * header) {

   assert(summary != NULL, "just checking");

   if (header != NULL) {

     gclog_or_tty->print_cr("%s", header);

   }

 #if CARD_REPEAT_HISTO

   gclog_or_tty->print_cr("\nG1 card_repeat count histogram: ");

   gclog_or_tty->print_cr("  # of repeats --> # of cards with that number.");

   card_repeat_count.print_on(gclog_or_tty);

 #endif

   summary->print_on(gclog_or_tty);

 }

 void G1RemSet::prepare_for_verify() {

   if (G1HRRSFlushLogBuffersOnVerify &&

       (VerifyBeforeGC || VerifyAfterGC)

       &&  (!_g1->full_collection() || G1VerifyRSetsDuringFullGC)) {

     cleanupHRRS();

     _g1->set_refine_cte_cl_concurrency(false);

     if (SafepointSynchronize::is_at_safepoint()) {

       DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();

       dcqs.concatenate_logs();

     }

     G1HotCardCache* hot_card_cache = _cg1r->hot_card_cache();

     bool use_hot_card_cache = hot_card_cache->use_cache();

     hot_card_cache->set_use_cache(false);

     DirtyCardQueue into_cset_dcq(&_g1->into_cset_dirty_card_queue_set());

     updateRS(&into_cset_dcq, 0);

     _g1->into_cset_dirty_card_queue_set().clear();

     hot_card_cache->set_use_cache(use_hot_card_cache);

     assert(JavaThread::dirty_card_queue_set().completed_buffers_num() == 0, "All should be consumed");

   }

 }