src/hotspot/share/gc/shared/cardTableRS.cpp
author coleenp
Tue, 03 Oct 2017 16:42:04 -0400
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child 49164 7e958a8ebcd3
permissions -rw-r--r--
8186777: Make Klass::_java_mirror an OopHandle Summary: Add indirection for fetching mirror so that GC doesn't have to follow CLD::_klasses Reviewed-by: hseigel, thartmann, eosterlund, stefank Contributed-by: coleen.phillimore@oracle.com, rickard.backman@oracle.com
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/*
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 * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 *
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 */
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#include "precompiled.hpp"
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#include "gc/shared/cardTableRS.hpp"
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#include "gc/shared/genCollectedHeap.hpp"
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#include "gc/shared/generation.hpp"
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#include "gc/shared/space.inline.hpp"
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#include "memory/allocation.inline.hpp"
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#include "oops/oop.inline.hpp"
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#include "runtime/atomic.hpp"
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#include "runtime/java.hpp"
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#include "runtime/os.hpp"
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#include "utilities/macros.hpp"
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class HasAccumulatedModifiedOopsClosure : public CLDClosure {
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  bool _found;
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 public:
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  HasAccumulatedModifiedOopsClosure() : _found(false) {}
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  void do_cld(ClassLoaderData* cld) {
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    if (_found) {
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      return;
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    }
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    if (cld->has_accumulated_modified_oops()) {
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      _found = true;
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    }
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  }
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  bool found() {
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    return _found;
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  }
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};
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bool CLDRemSet::mod_union_is_clear() {
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  HasAccumulatedModifiedOopsClosure closure;
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  ClassLoaderDataGraph::cld_do(&closure);
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  return !closure.found();
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}
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class ClearCLDModUnionClosure : public CLDClosure {
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 public:
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  void do_cld(ClassLoaderData* cld) {
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    if (cld->has_accumulated_modified_oops()) {
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      cld->clear_accumulated_modified_oops();
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    }
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  }
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};
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void CLDRemSet::clear_mod_union() {
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  ClearCLDModUnionClosure closure;
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  ClassLoaderDataGraph::cld_do(&closure);
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}
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CardTableRS::CardTableRS(MemRegion whole_heap) :
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  _bs(NULL),
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  _cur_youngergen_card_val(youngergenP1_card)
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{
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  _ct_bs = new CardTableModRefBSForCTRS(whole_heap);
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  _ct_bs->initialize();
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  set_bs(_ct_bs);
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  // max_gens is really GenCollectedHeap::heap()->gen_policy()->number_of_generations()
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  // (which is always 2, young & old), but GenCollectedHeap has not been initialized yet.
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  uint max_gens = 2;
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  _last_cur_val_in_gen = NEW_C_HEAP_ARRAY3(jbyte, max_gens + 1,
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                         mtGC, CURRENT_PC, AllocFailStrategy::RETURN_NULL);
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  if (_last_cur_val_in_gen == NULL) {
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    vm_exit_during_initialization("Could not create last_cur_val_in_gen array.");
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  }
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  for (uint i = 0; i < max_gens + 1; i++) {
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    _last_cur_val_in_gen[i] = clean_card_val();
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  }
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  _ct_bs->set_CTRS(this);
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}
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CardTableRS::~CardTableRS() {
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  if (_ct_bs) {
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    delete _ct_bs;
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    _ct_bs = NULL;
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  }
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  if (_last_cur_val_in_gen) {
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    FREE_C_HEAP_ARRAY(jbyte, _last_cur_val_in_gen);
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  }
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}
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void CardTableRS::resize_covered_region(MemRegion new_region) {
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  _ct_bs->resize_covered_region(new_region);
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}
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jbyte CardTableRS::find_unused_youngergenP_card_value() {
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  for (jbyte v = youngergenP1_card;
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       v < cur_youngergen_and_prev_nonclean_card;
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       v++) {
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    bool seen = false;
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    for (int g = 0; g < _regions_to_iterate; g++) {
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      if (_last_cur_val_in_gen[g] == v) {
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        seen = true;
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        break;
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      }
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    }
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    if (!seen) {
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      return v;
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    }
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  }
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  ShouldNotReachHere();
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  return 0;
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}
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void CardTableRS::prepare_for_younger_refs_iterate(bool parallel) {
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  // Parallel or sequential, we must always set the prev to equal the
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  // last one written.
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  if (parallel) {
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    // Find a parallel value to be used next.
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    jbyte next_val = find_unused_youngergenP_card_value();
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    set_cur_youngergen_card_val(next_val);
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  } else {
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    // In an sequential traversal we will always write youngergen, so that
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    // the inline barrier is  correct.
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    set_cur_youngergen_card_val(youngergen_card);
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  }
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}
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void CardTableRS::younger_refs_iterate(Generation* g,
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                                       OopsInGenClosure* blk,
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                                       uint n_threads) {
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  // The indexing in this array is slightly odd. We want to access
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  // the old generation record here, which is at index 2.
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  _last_cur_val_in_gen[2] = cur_youngergen_card_val();
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  g->younger_refs_iterate(blk, n_threads);
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}
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inline bool ClearNoncleanCardWrapper::clear_card(jbyte* entry) {
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  if (_is_par) {
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    return clear_card_parallel(entry);
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  } else {
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    return clear_card_serial(entry);
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  }
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}
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   163
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inline bool ClearNoncleanCardWrapper::clear_card_parallel(jbyte* entry) {
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  while (true) {
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    // In the parallel case, we may have to do this several times.
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    jbyte entry_val = *entry;
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    assert(entry_val != CardTableRS::clean_card_val(),
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           "We shouldn't be looking at clean cards, and this should "
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           "be the only place they get cleaned.");
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    if (CardTableRS::card_is_dirty_wrt_gen_iter(entry_val)
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        || _ct->is_prev_youngergen_card_val(entry_val)) {
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      jbyte res =
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        Atomic::cmpxchg(CardTableRS::clean_card_val(), entry, entry_val);
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      if (res == entry_val) {
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        break;
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      } else {
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        assert(res == CardTableRS::cur_youngergen_and_prev_nonclean_card,
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               "The CAS above should only fail if another thread did "
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               "a GC write barrier.");
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      }
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    } else if (entry_val ==
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               CardTableRS::cur_youngergen_and_prev_nonclean_card) {
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      // Parallelism shouldn't matter in this case.  Only the thread
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      // assigned to scan the card should change this value.
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      *entry = _ct->cur_youngergen_card_val();
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      break;
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    } else {
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      assert(entry_val == _ct->cur_youngergen_card_val(),
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             "Should be the only possibility.");
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      // In this case, the card was clean before, and become
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      // cur_youngergen only because of processing of a promoted object.
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      // We don't have to look at the card.
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      return false;
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    }
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  }
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  return true;
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}
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inline bool ClearNoncleanCardWrapper::clear_card_serial(jbyte* entry) {
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  jbyte entry_val = *entry;
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  assert(entry_val != CardTableRS::clean_card_val(),
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         "We shouldn't be looking at clean cards, and this should "
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         "be the only place they get cleaned.");
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  assert(entry_val != CardTableRS::cur_youngergen_and_prev_nonclean_card,
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         "This should be possible in the sequential case.");
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  *entry = CardTableRS::clean_card_val();
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  return true;
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}
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ClearNoncleanCardWrapper::ClearNoncleanCardWrapper(
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  DirtyCardToOopClosure* dirty_card_closure, CardTableRS* ct, bool is_par) :
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    _dirty_card_closure(dirty_card_closure), _ct(ct), _is_par(is_par) {
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}
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bool ClearNoncleanCardWrapper::is_word_aligned(jbyte* entry) {
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  return (((intptr_t)entry) & (BytesPerWord-1)) == 0;
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}
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// The regions are visited in *decreasing* address order.
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// This order aids with imprecise card marking, where a dirty
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// card may cause scanning, and summarization marking, of objects
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// that extend onto subsequent cards.
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void ClearNoncleanCardWrapper::do_MemRegion(MemRegion mr) {
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  assert(mr.word_size() > 0, "Error");
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  assert(_ct->is_aligned(mr.start()), "mr.start() should be card aligned");
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  // mr.end() may not necessarily be card aligned.
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  jbyte* cur_entry = _ct->byte_for(mr.last());
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  const jbyte* limit = _ct->byte_for(mr.start());
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  HeapWord* end_of_non_clean = mr.end();
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  HeapWord* start_of_non_clean = end_of_non_clean;
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  while (cur_entry >= limit) {
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    HeapWord* cur_hw = _ct->addr_for(cur_entry);
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    if ((*cur_entry != CardTableRS::clean_card_val()) && clear_card(cur_entry)) {
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      // Continue the dirty range by opening the
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      // dirty window one card to the left.
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      start_of_non_clean = cur_hw;
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    } else {
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      // We hit a "clean" card; process any non-empty
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      // "dirty" range accumulated so far.
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      if (start_of_non_clean < end_of_non_clean) {
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        const MemRegion mrd(start_of_non_clean, end_of_non_clean);
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        _dirty_card_closure->do_MemRegion(mrd);
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      }
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      // fast forward through potential continuous whole-word range of clean cards beginning at a word-boundary
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      if (is_word_aligned(cur_entry)) {
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        jbyte* cur_row = cur_entry - BytesPerWord;
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        while (cur_row >= limit && *((intptr_t*)cur_row) ==  CardTableRS::clean_card_row()) {
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          cur_row -= BytesPerWord;
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        }
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        cur_entry = cur_row + BytesPerWord;
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        cur_hw = _ct->addr_for(cur_entry);
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      }
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   256
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      // Reset the dirty window, while continuing to look
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      // for the next dirty card that will start a
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      // new dirty window.
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      end_of_non_clean = cur_hw;
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      start_of_non_clean = cur_hw;
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   262
    }
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    // Note that "cur_entry" leads "start_of_non_clean" in
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    // its leftward excursion after this point
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    // in the loop and, when we hit the left end of "mr",
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    // will point off of the left end of the card-table
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    // for "mr".
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    cur_entry--;
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  }
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  // If the first card of "mr" was dirty, we will have
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  // been left with a dirty window, co-initial with "mr",
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  // which we now process.
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  if (start_of_non_clean < end_of_non_clean) {
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    const MemRegion mrd(start_of_non_clean, end_of_non_clean);
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    _dirty_card_closure->do_MemRegion(mrd);
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  }
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}
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// clean (by dirty->clean before) ==> cur_younger_gen
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// dirty                          ==> cur_youngergen_and_prev_nonclean_card
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// precleaned                     ==> cur_youngergen_and_prev_nonclean_card
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// prev-younger-gen               ==> cur_youngergen_and_prev_nonclean_card
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// cur-younger-gen                ==> cur_younger_gen
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// cur_youngergen_and_prev_nonclean_card ==> no change.
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   285
void CardTableRS::write_ref_field_gc_par(void* field, oop new_val) {
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  volatile jbyte* entry = _ct_bs->byte_for(field);
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  do {
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    jbyte entry_val = *entry;
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    // We put this first because it's probably the most common case.
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    if (entry_val == clean_card_val()) {
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      // No threat of contention with cleaning threads.
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   292
      *entry = cur_youngergen_card_val();
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      return;
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   294
    } else if (card_is_dirty_wrt_gen_iter(entry_val)
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   295
               || is_prev_youngergen_card_val(entry_val)) {
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   296
      // Mark it as both cur and prev youngergen; card cleaning thread will
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   297
      // eventually remove the previous stuff.
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   298
      jbyte new_val = cur_youngergen_and_prev_nonclean_card;
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      jbyte res = Atomic::cmpxchg(new_val, entry, entry_val);
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      // Did the CAS succeed?
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      if (res == entry_val) return;
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      // Otherwise, retry, to see the new value.
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      continue;
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   304
    } else {
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   305
      assert(entry_val == cur_youngergen_and_prev_nonclean_card
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             || entry_val == cur_youngergen_card_val(),
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   307
             "should be only possibilities.");
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      return;
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    }
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  } while (true);
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}
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void CardTableRS::younger_refs_in_space_iterate(Space* sp,
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                                                OopsInGenClosure* cl,
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diff changeset
   315
                                                uint n_threads) {
9342
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diff changeset
   316
  const MemRegion urasm = sp->used_region_at_save_marks();
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diff changeset
   317
#ifdef ASSERT
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parents: 9336
diff changeset
   318
  // Convert the assertion check to a warning if we are running
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
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parents: 9336
diff changeset
   319
  // CMS+ParNew until related bug is fixed.
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
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parents: 9336
diff changeset
   320
  MemRegion ur    = sp->used_region();
27898
813ad96387b3 8065972: Remove support for ParNew+SerialOld and DefNew+CMS
brutisso
parents: 27687
diff changeset
   321
  assert(ur.contains(urasm) || (UseConcMarkSweepGC),
33105
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parents: 32623
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   322
         "Did you forget to call save_marks()? "
294e48b4f704 8080775: Better argument formatting for assert() and friends
david
parents: 32623
diff changeset
   323
         "[" PTR_FORMAT ", " PTR_FORMAT ") is not contained in "
294e48b4f704 8080775: Better argument formatting for assert() and friends
david
parents: 32623
diff changeset
   324
         "[" PTR_FORMAT ", " PTR_FORMAT ")",
294e48b4f704 8080775: Better argument formatting for assert() and friends
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parents: 32623
diff changeset
   325
         p2i(urasm.start()), p2i(urasm.end()), p2i(ur.start()), p2i(ur.end()));
9342
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
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parents: 9336
diff changeset
   326
  // In the case of CMS+ParNew, issue a warning
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
ysr
parents: 9336
diff changeset
   327
  if (!ur.contains(urasm)) {
27898
813ad96387b3 8065972: Remove support for ParNew+SerialOld and DefNew+CMS
brutisso
parents: 27687
diff changeset
   328
    assert(UseConcMarkSweepGC, "Tautology: see assert above");
37073
c39d0903390b 8151605: Change warning() to log_warning(gc) in the GC code
brutisso
parents: 33230
diff changeset
   329
    log_warning(gc)("CMS+ParNew: Did you forget to call save_marks()? "
c39d0903390b 8151605: Change warning() to log_warning(gc) in the GC code
brutisso
parents: 33230
diff changeset
   330
                    "[" PTR_FORMAT ", " PTR_FORMAT ") is not contained in "
c39d0903390b 8151605: Change warning() to log_warning(gc) in the GC code
brutisso
parents: 33230
diff changeset
   331
                    "[" PTR_FORMAT ", " PTR_FORMAT ")",
c39d0903390b 8151605: Change warning() to log_warning(gc) in the GC code
brutisso
parents: 33230
diff changeset
   332
                    p2i(urasm.start()), p2i(urasm.end()), p2i(ur.start()), p2i(ur.end()));
9342
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
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parents: 9336
diff changeset
   333
    MemRegion ur2 = sp->used_region();
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
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parents: 9336
diff changeset
   334
    MemRegion urasm2 = sp->used_region_at_save_marks();
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
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parents: 9336
diff changeset
   335
    if (!ur.equals(ur2)) {
37073
c39d0903390b 8151605: Change warning() to log_warning(gc) in the GC code
brutisso
parents: 33230
diff changeset
   336
      log_warning(gc)("CMS+ParNew: Flickering used_region()!!");
9342
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
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parents: 9336
diff changeset
   337
    }
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
ysr
parents: 9336
diff changeset
   338
    if (!urasm.equals(urasm2)) {
37073
c39d0903390b 8151605: Change warning() to log_warning(gc) in the GC code
brutisso
parents: 33230
diff changeset
   339
      log_warning(gc)("CMS+ParNew: Flickering used_region_at_save_marks()!!");
9342
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
ysr
parents: 9336
diff changeset
   340
    }
9624
c3657c3324ee 6883834: ParNew: assert(!_g->to()->is_in_reserved(obj),"Scanning field twice?") with LargeObjects tests
ysr
parents: 9342
diff changeset
   341
    ShouldNotReachHere();
9342
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
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diff changeset
   342
  }
456b8d0486b5 7039089: G1: changeset for 7037276 broke heap verification, and related cleanups
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diff changeset
   343
#endif
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stefank
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   344
  _ct_bs->non_clean_card_iterate_possibly_parallel(sp, urasm, cl, this, n_threads);
1
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   345
}
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   346
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diff changeset
   347
void CardTableRS::clear_into_younger(Generation* old_gen) {
31358
693058672cc6 8077842: Remove the level parameter passed around in GenCollectedHeap
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diff changeset
   348
  assert(GenCollectedHeap::heap()->is_old_gen(old_gen),
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   349
         "Should only be called for the old generation");
19289
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   350
  // The card tables for the youngest gen need never be cleared.
1
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parents:
diff changeset
   351
  // There's a bit of subtlety in the clear() and invalidate()
489c9b5090e2 Initial load
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parents:
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   352
  // methods that we exploit here and in invalidate_or_clear()
489c9b5090e2 Initial load
duke
parents:
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   353
  // below to avoid missing cards at the fringes. If clear() or
489c9b5090e2 Initial load
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parents:
diff changeset
   354
  // invalidate() are changed in the future, this code should
489c9b5090e2 Initial load
duke
parents:
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   355
  // be revisited. 20040107.ysr
19286
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brutisso
parents: 17376
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   356
  clear(old_gen->prev_used_region());
1
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parents:
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   357
}
489c9b5090e2 Initial load
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   358
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   359
void CardTableRS::invalidate_or_clear(Generation* old_gen) {
31358
693058672cc6 8077842: Remove the level parameter passed around in GenCollectedHeap
jwilhelm
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diff changeset
   360
  assert(GenCollectedHeap::heap()->is_old_gen(old_gen),
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diff changeset
   361
         "Should only be called for the old generation");
19289
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diff changeset
   362
  // Invalidate the cards for the currently occupied part of
213031f03f61 8023021: Unnecessary clearing of the card table introduced by the fix for JDK-8023013
brutisso
parents: 19286
diff changeset
   363
  // the old generation and clear the cards for the
1
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parents:
diff changeset
   364
  // unoccupied part of the generation (if any, making use
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parents:
diff changeset
   365
  // of that generation's prev_used_region to determine that
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parents:
diff changeset
   366
  // region). No need to do anything for the youngest
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parents:
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   367
  // generation. Also see note#20040107.ysr above.
19289
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parents: 19286
diff changeset
   368
  MemRegion used_mr = old_gen->used_region();
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parents: 19286
diff changeset
   369
  MemRegion to_be_cleared_mr = old_gen->prev_used_region().minus(used_mr);
19286
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brutisso
parents: 17376
diff changeset
   370
  if (!to_be_cleared_mr.is_empty()) {
48394008c803 8022800: Use specific generations rather than generation iteration
brutisso
parents: 17376
diff changeset
   371
    clear(to_be_cleared_mr);
1
489c9b5090e2 Initial load
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parents:
diff changeset
   372
  }
19286
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brutisso
parents: 17376
diff changeset
   373
  invalidate(used_mr);
1
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parents:
diff changeset
   374
}
489c9b5090e2 Initial load
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parents:
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   375
489c9b5090e2 Initial load
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parents:
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   376
489c9b5090e2 Initial load
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parents:
diff changeset
   377
class VerifyCleanCardClosure: public OopClosure {
360
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
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parents: 179
diff changeset
   378
private:
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
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parents: 179
diff changeset
   379
  HeapWord* _boundary;
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
coleenp
parents: 179
diff changeset
   380
  HeapWord* _begin;
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
coleenp
parents: 179
diff changeset
   381
  HeapWord* _end;
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
coleenp
parents: 179
diff changeset
   382
protected:
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
coleenp
parents: 179
diff changeset
   383
  template <class T> void do_oop_work(T* p) {
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   384
    HeapWord* jp = (HeapWord*)p;
8923
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   385
    assert(jp >= _begin && jp < _end,
33105
294e48b4f704 8080775: Better argument formatting for assert() and friends
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parents: 32623
diff changeset
   386
           "Error: jp " PTR_FORMAT " should be within "
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david
parents: 32623
diff changeset
   387
           "[_begin, _end) = [" PTR_FORMAT "," PTR_FORMAT ")",
294e48b4f704 8080775: Better argument formatting for assert() and friends
david
parents: 32623
diff changeset
   388
           p2i(jp), p2i(_begin), p2i(_end));
8923
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
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parents: 7397
diff changeset
   389
    oop obj = oopDesc::load_decode_heap_oop(p);
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   390
    guarantee(obj == NULL || (HeapWord*)obj >= _boundary,
33105
294e48b4f704 8080775: Better argument formatting for assert() and friends
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parents: 32623
diff changeset
   391
              "pointer " PTR_FORMAT " at " PTR_FORMAT " on "
294e48b4f704 8080775: Better argument formatting for assert() and friends
david
parents: 32623
diff changeset
   392
              "clean card crosses boundary" PTR_FORMAT,
33198
dlong
parents: 33105 33160
diff changeset
   393
              p2i(obj), p2i(jp), p2i(_boundary));
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   394
  }
8923
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
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parents: 7397
diff changeset
   395
360
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
coleenp
parents: 179
diff changeset
   396
public:
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
coleenp
parents: 179
diff changeset
   397
  VerifyCleanCardClosure(HeapWord* b, HeapWord* begin, HeapWord* end) :
8923
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   398
    _boundary(b), _begin(begin), _end(end) {
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   399
    assert(b <= begin,
33105
294e48b4f704 8080775: Better argument formatting for assert() and friends
david
parents: 32623
diff changeset
   400
           "Error: boundary " PTR_FORMAT " should be at or below begin " PTR_FORMAT,
294e48b4f704 8080775: Better argument formatting for assert() and friends
david
parents: 32623
diff changeset
   401
           p2i(b), p2i(begin));
8923
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   402
    assert(begin <= end,
33105
294e48b4f704 8080775: Better argument formatting for assert() and friends
david
parents: 32623
diff changeset
   403
           "Error: begin " PTR_FORMAT " should be strictly below end " PTR_FORMAT,
294e48b4f704 8080775: Better argument formatting for assert() and friends
david
parents: 32623
diff changeset
   404
           p2i(begin), p2i(end));
8923
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   405
  }
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   406
360
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
coleenp
parents: 179
diff changeset
   407
  virtual void do_oop(oop* p)       { VerifyCleanCardClosure::do_oop_work(p); }
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
coleenp
parents: 179
diff changeset
   408
  virtual void do_oop(narrowOop* p) { VerifyCleanCardClosure::do_oop_work(p); }
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   409
};
489c9b5090e2 Initial load
duke
parents:
diff changeset
   410
489c9b5090e2 Initial load
duke
parents:
diff changeset
   411
class VerifyCTSpaceClosure: public SpaceClosure {
360
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
coleenp
parents: 179
diff changeset
   412
private:
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   413
  CardTableRS* _ct;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   414
  HeapWord* _boundary;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   415
public:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   416
  VerifyCTSpaceClosure(CardTableRS* ct, HeapWord* boundary) :
489c9b5090e2 Initial load
duke
parents:
diff changeset
   417
    _ct(ct), _boundary(boundary) {}
360
21d113ecbf6a 6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
coleenp
parents: 179
diff changeset
   418
  virtual void do_space(Space* s) { _ct->verify_space(s, _boundary); }
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   419
};
489c9b5090e2 Initial load
duke
parents:
diff changeset
   420
489c9b5090e2 Initial load
duke
parents:
diff changeset
   421
class VerifyCTGenClosure: public GenCollectedHeap::GenClosure {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   422
  CardTableRS* _ct;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   423
public:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   424
  VerifyCTGenClosure(CardTableRS* ct) : _ct(ct) {}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   425
  void do_generation(Generation* gen) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   426
    // Skip the youngest generation.
31358
693058672cc6 8077842: Remove the level parameter passed around in GenCollectedHeap
jwilhelm
parents: 30870
diff changeset
   427
    if (GenCollectedHeap::heap()->is_young_gen(gen)) {
693058672cc6 8077842: Remove the level parameter passed around in GenCollectedHeap
jwilhelm
parents: 30870
diff changeset
   428
      return;
693058672cc6 8077842: Remove the level parameter passed around in GenCollectedHeap
jwilhelm
parents: 30870
diff changeset
   429
    }
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   430
    // Normally, we're interested in pointers to younger generations.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   431
    VerifyCTSpaceClosure blk(_ct, gen->reserved().start());
489c9b5090e2 Initial load
duke
parents:
diff changeset
   432
    gen->space_iterate(&blk, true);
489c9b5090e2 Initial load
duke
parents:
diff changeset
   433
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   434
};
489c9b5090e2 Initial load
duke
parents:
diff changeset
   435
489c9b5090e2 Initial load
duke
parents:
diff changeset
   436
void CardTableRS::verify_space(Space* s, HeapWord* gen_boundary) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   437
  // We don't need to do young-gen spaces.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   438
  if (s->end() <= gen_boundary) return;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   439
  MemRegion used = s->used_region();
489c9b5090e2 Initial load
duke
parents:
diff changeset
   440
489c9b5090e2 Initial load
duke
parents:
diff changeset
   441
  jbyte* cur_entry = byte_for(used.start());
489c9b5090e2 Initial load
duke
parents:
diff changeset
   442
  jbyte* limit = byte_after(used.last());
489c9b5090e2 Initial load
duke
parents:
diff changeset
   443
  while (cur_entry < limit) {
31964
d34ad1715d96 8130931: Refactor CardTableModRefBS[ForCTRS]
kbarrett
parents: 31358
diff changeset
   444
    if (*cur_entry == clean_card_val()) {
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   445
      jbyte* first_dirty = cur_entry+1;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   446
      while (first_dirty < limit &&
31964
d34ad1715d96 8130931: Refactor CardTableModRefBS[ForCTRS]
kbarrett
parents: 31358
diff changeset
   447
             *first_dirty == clean_card_val()) {
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   448
        first_dirty++;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   449
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   450
      // If the first object is a regular object, and it has a
489c9b5090e2 Initial load
duke
parents:
diff changeset
   451
      // young-to-old field, that would mark the previous card.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   452
      HeapWord* boundary = addr_for(cur_entry);
489c9b5090e2 Initial load
duke
parents:
diff changeset
   453
      HeapWord* end = (first_dirty >= limit) ? used.end() : addr_for(first_dirty);
489c9b5090e2 Initial load
duke
parents:
diff changeset
   454
      HeapWord* boundary_block = s->block_start(boundary);
489c9b5090e2 Initial load
duke
parents:
diff changeset
   455
      HeapWord* begin = boundary;             // Until proven otherwise.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   456
      HeapWord* start_block = boundary_block; // Until proven otherwise.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   457
      if (boundary_block < boundary) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   458
        if (s->block_is_obj(boundary_block) && s->obj_is_alive(boundary_block)) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   459
          oop boundary_obj = oop(boundary_block);
489c9b5090e2 Initial load
duke
parents:
diff changeset
   460
          if (!boundary_obj->is_objArray() &&
489c9b5090e2 Initial load
duke
parents:
diff changeset
   461
              !boundary_obj->is_typeArray()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   462
            guarantee(cur_entry > byte_for(used.start()),
489c9b5090e2 Initial load
duke
parents:
diff changeset
   463
                      "else boundary would be boundary_block");
31964
d34ad1715d96 8130931: Refactor CardTableModRefBS[ForCTRS]
kbarrett
parents: 31358
diff changeset
   464
            if (*byte_for(boundary_block) != clean_card_val()) {
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   465
              begin = boundary_block + s->block_size(boundary_block);
489c9b5090e2 Initial load
duke
parents:
diff changeset
   466
              start_block = begin;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   467
            }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   468
          }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   469
        }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   470
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   471
      // Now traverse objects until end.
8923
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   472
      if (begin < end) {
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   473
        MemRegion mr(begin, end);
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   474
        VerifyCleanCardClosure verify_blk(gen_boundary, begin, end);
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   475
        for (HeapWord* cur = start_block; cur < end; cur += s->block_size(cur)) {
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   476
          if (s->block_is_obj(cur) && s->obj_is_alive(cur)) {
13728
882756847a04 6964458: Reimplement class meta-data storage to use native memory
coleenp
parents: 12118
diff changeset
   477
            oop(cur)->oop_iterate_no_header(&verify_blk, mr);
8923
67b8a1ea66e2 7029036: Card-table verification hangs with all framework collectors, except G1, even before the first GC
ysr
parents: 7397
diff changeset
   478
          }
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   479
        }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   480
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   481
      cur_entry = first_dirty;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   482
    } else {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   483
      // We'd normally expect that cur_youngergen_and_prev_nonclean_card
489c9b5090e2 Initial load
duke
parents:
diff changeset
   484
      // is a transient value, that cannot be in the card table
489c9b5090e2 Initial load
duke
parents:
diff changeset
   485
      // except during GC, and thus assert that:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   486
      // guarantee(*cur_entry != cur_youngergen_and_prev_nonclean_card,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   487
      //        "Illegal CT value");
489c9b5090e2 Initial load
duke
parents:
diff changeset
   488
      // That however, need not hold, as will become clear in the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   489
      // following...
489c9b5090e2 Initial load
duke
parents:
diff changeset
   490
489c9b5090e2 Initial load
duke
parents:
diff changeset
   491
      // We'd normally expect that if we are in the parallel case,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   492
      // we can't have left a prev value (which would be different
489c9b5090e2 Initial load
duke
parents:
diff changeset
   493
      // from the current value) in the card table, and so we'd like to
489c9b5090e2 Initial load
duke
parents:
diff changeset
   494
      // assert that:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   495
      // guarantee(cur_youngergen_card_val() == youngergen_card
489c9b5090e2 Initial load
duke
parents:
diff changeset
   496
      //           || !is_prev_youngergen_card_val(*cur_entry),
489c9b5090e2 Initial load
duke
parents:
diff changeset
   497
      //           "Illegal CT value");
489c9b5090e2 Initial load
duke
parents:
diff changeset
   498
      // That, however, may not hold occasionally, because of
489c9b5090e2 Initial load
duke
parents:
diff changeset
   499
      // CMS or MSC in the old gen. To wit, consider the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   500
      // following two simple illustrative scenarios:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   501
      // (a) CMS: Consider the case where a large object L
489c9b5090e2 Initial load
duke
parents:
diff changeset
   502
      //     spanning several cards is allocated in the old
489c9b5090e2 Initial load
duke
parents:
diff changeset
   503
      //     gen, and has a young gen reference stored in it, dirtying
489c9b5090e2 Initial load
duke
parents:
diff changeset
   504
      //     some interior cards. A young collection scans the card,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   505
      //     finds a young ref and installs a youngergenP_n value.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   506
      //     L then goes dead. Now a CMS collection starts,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   507
      //     finds L dead and sweeps it up. Assume that L is
489c9b5090e2 Initial load
duke
parents:
diff changeset
   508
      //     abutting _unallocated_blk, so _unallocated_blk is
489c9b5090e2 Initial load
duke
parents:
diff changeset
   509
      //     adjusted down to (below) L. Assume further that
489c9b5090e2 Initial load
duke
parents:
diff changeset
   510
      //     no young collection intervenes during this CMS cycle.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   511
      //     The next young gen cycle will not get to look at this
489c9b5090e2 Initial load
duke
parents:
diff changeset
   512
      //     youngergenP_n card since it lies in the unoccupied
489c9b5090e2 Initial load
duke
parents:
diff changeset
   513
      //     part of the space.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   514
      //     Some young collections later the blocks on this
489c9b5090e2 Initial load
duke
parents:
diff changeset
   515
      //     card can be re-allocated either due to direct allocation
489c9b5090e2 Initial load
duke
parents:
diff changeset
   516
      //     or due to absorbing promotions. At this time, the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   517
      //     before-gc verification will fail the above assert.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   518
      // (b) MSC: In this case, an object L with a young reference
489c9b5090e2 Initial load
duke
parents:
diff changeset
   519
      //     is on a card that (therefore) holds a youngergen_n value.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   520
      //     Suppose also that L lies towards the end of the used
489c9b5090e2 Initial load
duke
parents:
diff changeset
   521
      //     the used space before GC. An MSC collection
489c9b5090e2 Initial load
duke
parents:
diff changeset
   522
      //     occurs that compacts to such an extent that this
489c9b5090e2 Initial load
duke
parents:
diff changeset
   523
      //     card is no longer in the occupied part of the space.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   524
      //     Since current code in MSC does not always clear cards
489c9b5090e2 Initial load
duke
parents:
diff changeset
   525
      //     in the unused part of old gen, this stale youngergen_n
489c9b5090e2 Initial load
duke
parents:
diff changeset
   526
      //     value is left behind and can later be covered by
489c9b5090e2 Initial load
duke
parents:
diff changeset
   527
      //     an object when promotion or direct allocation
489c9b5090e2 Initial load
duke
parents:
diff changeset
   528
      //     re-allocates that part of the heap.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   529
      //
489c9b5090e2 Initial load
duke
parents:
diff changeset
   530
      // Fortunately, the presence of such stale card values is
489c9b5090e2 Initial load
duke
parents:
diff changeset
   531
      // "only" a minor annoyance in that subsequent young collections
489c9b5090e2 Initial load
duke
parents:
diff changeset
   532
      // might needlessly scan such cards, but would still never corrupt
489c9b5090e2 Initial load
duke
parents:
diff changeset
   533
      // the heap as a result. However, it's likely not to be a significant
489c9b5090e2 Initial load
duke
parents:
diff changeset
   534
      // performance inhibitor in practice. For instance,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   535
      // some recent measurements with unoccupied cards eagerly cleared
489c9b5090e2 Initial load
duke
parents:
diff changeset
   536
      // out to maintain this invariant, showed next to no
489c9b5090e2 Initial load
duke
parents:
diff changeset
   537
      // change in young collection times; of course one can construct
489c9b5090e2 Initial load
duke
parents:
diff changeset
   538
      // degenerate examples where the cost can be significant.)
489c9b5090e2 Initial load
duke
parents:
diff changeset
   539
      // Note, in particular, that if the "stale" card is modified
489c9b5090e2 Initial load
duke
parents:
diff changeset
   540
      // after re-allocation, it would be dirty, not "stale". Thus,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   541
      // we can never have a younger ref in such a card and it is
489c9b5090e2 Initial load
duke
parents:
diff changeset
   542
      // safe not to scan that card in any collection. [As we see
489c9b5090e2 Initial load
duke
parents:
diff changeset
   543
      // below, we do some unnecessary scanning
489c9b5090e2 Initial load
duke
parents:
diff changeset
   544
      // in some cases in the current parallel scanning algorithm.]
489c9b5090e2 Initial load
duke
parents:
diff changeset
   545
      //
489c9b5090e2 Initial load
duke
parents:
diff changeset
   546
      // The main point below is that the parallel card scanning code
489c9b5090e2 Initial load
duke
parents:
diff changeset
   547
      // deals correctly with these stale card values. There are two main
32623
390a27af5657 8134626: Misc cleanups after generation array removal
jwilhelm
parents: 31964
diff changeset
   548
      // cases to consider where we have a stale "young gen" value and a
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   549
      // "derivative" case to consider, where we have a stale
489c9b5090e2 Initial load
duke
parents:
diff changeset
   550
      // "cur_younger_gen_and_prev_non_clean" value, as will become
489c9b5090e2 Initial load
duke
parents:
diff changeset
   551
      // apparent in the case analysis below.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   552
      // o Case 1. If the stale value corresponds to a younger_gen_n
489c9b5090e2 Initial load
duke
parents:
diff changeset
   553
      //   value other than the cur_younger_gen value then the code
489c9b5090e2 Initial load
duke
parents:
diff changeset
   554
      //   treats this as being tantamount to a prev_younger_gen
489c9b5090e2 Initial load
duke
parents:
diff changeset
   555
      //   card. This means that the card may be unnecessarily scanned.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   556
      //   There are two sub-cases to consider:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   557
      //   o Case 1a. Let us say that the card is in the occupied part
489c9b5090e2 Initial load
duke
parents:
diff changeset
   558
      //     of the generation at the time the collection begins. In
489c9b5090e2 Initial load
duke
parents:
diff changeset
   559
      //     that case the card will be either cleared when it is scanned
489c9b5090e2 Initial load
duke
parents:
diff changeset
   560
      //     for young pointers, or will be set to cur_younger_gen as a
489c9b5090e2 Initial load
duke
parents:
diff changeset
   561
      //     result of promotion. (We have elided the normal case where
489c9b5090e2 Initial load
duke
parents:
diff changeset
   562
      //     the scanning thread and the promoting thread interleave
489c9b5090e2 Initial load
duke
parents:
diff changeset
   563
      //     possibly resulting in a transient
489c9b5090e2 Initial load
duke
parents:
diff changeset
   564
      //     cur_younger_gen_and_prev_non_clean value before settling
489c9b5090e2 Initial load
duke
parents:
diff changeset
   565
      //     to cur_younger_gen. [End Case 1a.]
489c9b5090e2 Initial load
duke
parents:
diff changeset
   566
      //   o Case 1b. Consider now the case when the card is in the unoccupied
489c9b5090e2 Initial load
duke
parents:
diff changeset
   567
      //     part of the space which becomes occupied because of promotions
489c9b5090e2 Initial load
duke
parents:
diff changeset
   568
      //     into it during the current young GC. In this case the card
489c9b5090e2 Initial load
duke
parents:
diff changeset
   569
      //     will never be scanned for young references. The current
489c9b5090e2 Initial load
duke
parents:
diff changeset
   570
      //     code will set the card value to either
489c9b5090e2 Initial load
duke
parents:
diff changeset
   571
      //     cur_younger_gen_and_prev_non_clean or leave
489c9b5090e2 Initial load
duke
parents:
diff changeset
   572
      //     it with its stale value -- because the promotions didn't
489c9b5090e2 Initial load
duke
parents:
diff changeset
   573
      //     result in any younger refs on that card. Of these two
489c9b5090e2 Initial load
duke
parents:
diff changeset
   574
      //     cases, the latter will be covered in Case 1a during
489c9b5090e2 Initial load
duke
parents:
diff changeset
   575
      //     a subsequent scan. To deal with the former case, we need
489c9b5090e2 Initial load
duke
parents:
diff changeset
   576
      //     to further consider how we deal with a stale value of
489c9b5090e2 Initial load
duke
parents:
diff changeset
   577
      //     cur_younger_gen_and_prev_non_clean in our case analysis
489c9b5090e2 Initial load
duke
parents:
diff changeset
   578
      //     below. This we do in Case 3 below. [End Case 1b]
489c9b5090e2 Initial load
duke
parents:
diff changeset
   579
      //   [End Case 1]
489c9b5090e2 Initial load
duke
parents:
diff changeset
   580
      // o Case 2. If the stale value corresponds to cur_younger_gen being
489c9b5090e2 Initial load
duke
parents:
diff changeset
   581
      //   a value not necessarily written by a current promotion, the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   582
      //   card will not be scanned by the younger refs scanning code.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   583
      //   (This is OK since as we argued above such cards cannot contain
489c9b5090e2 Initial load
duke
parents:
diff changeset
   584
      //   any younger refs.) The result is that this value will be
489c9b5090e2 Initial load
duke
parents:
diff changeset
   585
      //   treated as a prev_younger_gen value in a subsequent collection,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   586
      //   which is addressed in Case 1 above. [End Case 2]
489c9b5090e2 Initial load
duke
parents:
diff changeset
   587
      // o Case 3. We here consider the "derivative" case from Case 1b. above
489c9b5090e2 Initial load
duke
parents:
diff changeset
   588
      //   because of which we may find a stale
489c9b5090e2 Initial load
duke
parents:
diff changeset
   589
      //   cur_younger_gen_and_prev_non_clean card value in the table.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   590
      //   Once again, as in Case 1, we consider two subcases, depending
489c9b5090e2 Initial load
duke
parents:
diff changeset
   591
      //   on whether the card lies in the occupied or unoccupied part
489c9b5090e2 Initial load
duke
parents:
diff changeset
   592
      //   of the space at the start of the young collection.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   593
      //   o Case 3a. Let us say the card is in the occupied part of
489c9b5090e2 Initial load
duke
parents:
diff changeset
   594
      //     the old gen at the start of the young collection. In that
489c9b5090e2 Initial load
duke
parents:
diff changeset
   595
      //     case, the card will be scanned by the younger refs scanning
489c9b5090e2 Initial load
duke
parents:
diff changeset
   596
      //     code which will set it to cur_younger_gen. In a subsequent
489c9b5090e2 Initial load
duke
parents:
diff changeset
   597
      //     scan, the card will be considered again and get its final
489c9b5090e2 Initial load
duke
parents:
diff changeset
   598
      //     correct value. [End Case 3a]
489c9b5090e2 Initial load
duke
parents:
diff changeset
   599
      //   o Case 3b. Now consider the case where the card is in the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   600
      //     unoccupied part of the old gen, and is occupied as a result
489c9b5090e2 Initial load
duke
parents:
diff changeset
   601
      //     of promotions during thus young gc. In that case,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   602
      //     the card will not be scanned for younger refs. The presence
489c9b5090e2 Initial load
duke
parents:
diff changeset
   603
      //     of newly promoted objects on the card will then result in
489c9b5090e2 Initial load
duke
parents:
diff changeset
   604
      //     its keeping the value cur_younger_gen_and_prev_non_clean
489c9b5090e2 Initial load
duke
parents:
diff changeset
   605
      //     value, which we have dealt with in Case 3 here. [End Case 3b]
489c9b5090e2 Initial load
duke
parents:
diff changeset
   606
      //   [End Case 3]
489c9b5090e2 Initial load
duke
parents:
diff changeset
   607
      //
489c9b5090e2 Initial load
duke
parents:
diff changeset
   608
      // (Please refer to the code in the helper class
489c9b5090e2 Initial load
duke
parents:
diff changeset
   609
      // ClearNonCleanCardWrapper and in CardTableModRefBS for details.)
489c9b5090e2 Initial load
duke
parents:
diff changeset
   610
      //
489c9b5090e2 Initial load
duke
parents:
diff changeset
   611
      // The informal arguments above can be tightened into a formal
489c9b5090e2 Initial load
duke
parents:
diff changeset
   612
      // correctness proof and it behooves us to write up such a proof,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   613
      // or to use model checking to prove that there are no lingering
489c9b5090e2 Initial load
duke
parents:
diff changeset
   614
      // concerns.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   615
      //
489c9b5090e2 Initial load
duke
parents:
diff changeset
   616
      // Clearly because of Case 3b one cannot bound the time for
489c9b5090e2 Initial load
duke
parents:
diff changeset
   617
      // which a card will retain what we have called a "stale" value.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   618
      // However, one can obtain a Loose upper bound on the redundant
489c9b5090e2 Initial load
duke
parents:
diff changeset
   619
      // work as a result of such stale values. Note first that any
489c9b5090e2 Initial load
duke
parents:
diff changeset
   620
      // time a stale card lies in the occupied part of the space at
489c9b5090e2 Initial load
duke
parents:
diff changeset
   621
      // the start of the collection, it is scanned by younger refs
489c9b5090e2 Initial load
duke
parents:
diff changeset
   622
      // code and we can define a rank function on card values that
489c9b5090e2 Initial load
duke
parents:
diff changeset
   623
      // declines when this is so. Note also that when a card does not
489c9b5090e2 Initial load
duke
parents:
diff changeset
   624
      // lie in the occupied part of the space at the beginning of a
489c9b5090e2 Initial load
duke
parents:
diff changeset
   625
      // young collection, its rank can either decline or stay unchanged.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   626
      // In this case, no extra work is done in terms of redundant
489c9b5090e2 Initial load
duke
parents:
diff changeset
   627
      // younger refs scanning of that card.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   628
      // Then, the case analysis above reveals that, in the worst case,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   629
      // any such stale card will be scanned unnecessarily at most twice.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   630
      //
22551
9bf46d16dcc6 8025856: Fix typos in the GC code
jwilhelm
parents: 19289
diff changeset
   631
      // It is nonetheless advisable to try and get rid of some of this
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   632
      // redundant work in a subsequent (low priority) re-design of
489c9b5090e2 Initial load
duke
parents:
diff changeset
   633
      // the card-scanning code, if only to simplify the underlying
489c9b5090e2 Initial load
duke
parents:
diff changeset
   634
      // state machine analysis/proof. ysr 1/28/2002. XXX
489c9b5090e2 Initial load
duke
parents:
diff changeset
   635
      cur_entry++;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   636
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   637
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   638
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   639
489c9b5090e2 Initial load
duke
parents:
diff changeset
   640
void CardTableRS::verify() {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   641
  // At present, we only know how to verify the card table RS for
489c9b5090e2 Initial load
duke
parents:
diff changeset
   642
  // generational heaps.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   643
  VerifyCTGenClosure blk(this);
30173
13cf7580b000 8077413: Avoid use of Universe::heap() inside collectors
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diff changeset
   644
  GenCollectedHeap::heap()->generation_iterate(&blk, false);
13cf7580b000 8077413: Avoid use of Universe::heap() inside collectors
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parents: 30165
diff changeset
   645
  _ct_bs->verify();
13cf7580b000 8077413: Avoid use of Universe::heap() inside collectors
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parents: 30165
diff changeset
   646
}