view src/share/vm/gc_implementation/g1/g1MarkSweep.cpp @ 2534:6747fd0512e0

7004681: G1: Extend marking verification to Full GCs Summary: Perform a heap verification after the first phase of G1's full GC using objects' mark words to determine liveness. The third parameter of the heap verification routines, which was used in G1 to determine which marking bitmap to use in liveness calculations, has been changed from a boolean to an enum with values defined for using the mark word, and the 'prev' and 'next' bitmaps. Reviewed-by: tonyp, ysr
author johnc
date Tue, 14 Jun 2011 11:01:10 -0700
parents 1216415d8e35
children 4dfb2df418f2
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/*
 * Copyright (c) 2001, 2011, 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
 * questions.
 *
 */

#include "precompiled.hpp"
#include "classfile/javaClasses.hpp"
#include "classfile/symbolTable.hpp"
#include "classfile/systemDictionary.hpp"
#include "classfile/vmSymbols.hpp"
#include "code/codeCache.hpp"
#include "code/icBuffer.hpp"
#include "gc_implementation/g1/g1MarkSweep.hpp"
#include "memory/gcLocker.hpp"
#include "memory/genCollectedHeap.hpp"
#include "memory/modRefBarrierSet.hpp"
#include "memory/referencePolicy.hpp"
#include "memory/space.hpp"
#include "oops/instanceRefKlass.hpp"
#include "oops/oop.inline.hpp"
#include "prims/jvmtiExport.hpp"
#include "runtime/aprofiler.hpp"
#include "runtime/biasedLocking.hpp"
#include "runtime/fprofiler.hpp"
#include "runtime/synchronizer.hpp"
#include "runtime/thread.hpp"
#include "runtime/vmThread.hpp"
#include "utilities/copy.hpp"
#include "utilities/events.hpp"

class HeapRegion;

void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
                                      bool clear_all_softrefs) {
  assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");

  SharedHeap* sh = SharedHeap::heap();
#ifdef ASSERT
  if (sh->collector_policy()->should_clear_all_soft_refs()) {
    assert(clear_all_softrefs, "Policy should have been checked earler");
  }
#endif
  // hook up weak ref data so it can be used during Mark-Sweep
  assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
  assert(rp != NULL, "should be non-NULL");
  GenMarkSweep::_ref_processor = rp;
  rp->setup_policy(clear_all_softrefs);

  // When collecting the permanent generation methodOops may be moving,
  // so we either have to flush all bcp data or convert it into bci.
  CodeCache::gc_prologue();
  Threads::gc_prologue();

  // Increment the invocation count for the permanent generation, since it is
  // implicitly collected whenever we do a full mark sweep collection.
  sh->perm_gen()->stat_record()->invocations++;

  bool marked_for_unloading = false;

  allocate_stacks();

  // We should save the marks of the currently locked biased monitors.
  // The marking doesn't preserve the marks of biased objects.
  BiasedLocking::preserve_marks();

  mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);

  mark_sweep_phase2();

  // Don't add any more derived pointers during phase3
  COMPILER2_PRESENT(DerivedPointerTable::set_active(false));

  mark_sweep_phase3();

  mark_sweep_phase4();

  GenMarkSweep::restore_marks();
  BiasedLocking::restore_marks();
  GenMarkSweep::deallocate_stacks();

  // We must invalidate the perm-gen rs, so that it gets rebuilt.
  GenRemSet* rs = sh->rem_set();
  rs->invalidate(sh->perm_gen()->used_region(), true /*whole_heap*/);

  // "free at last gc" is calculated from these.
  // CHF: cheating for now!!!
  //  Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity());
  //  Universe::set_heap_used_at_last_gc(Universe::heap()->used());

  Threads::gc_epilogue();
  CodeCache::gc_epilogue();
  JvmtiExport::gc_epilogue();

  // refs processing: clean slate
  GenMarkSweep::_ref_processor = NULL;
}


void G1MarkSweep::allocate_stacks() {
  GenMarkSweep::_preserved_count_max = 0;
  GenMarkSweep::_preserved_marks = NULL;
  GenMarkSweep::_preserved_count = 0;
}

void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
                                    bool clear_all_softrefs) {
  // Recursively traverse all live objects and mark them
  EventMark m("1 mark object");
  TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
  GenMarkSweep::trace(" 1");

  SharedHeap* sh = SharedHeap::heap();

  sh->process_strong_roots(true,  // activeate StrongRootsScope
                           true,  // Collecting permanent generation.
                           SharedHeap::SO_SystemClasses,
                           &GenMarkSweep::follow_root_closure,
                           &GenMarkSweep::follow_code_root_closure,
                           &GenMarkSweep::follow_root_closure);

  // Process reference objects found during marking
  ReferenceProcessor* rp = GenMarkSweep::ref_processor();
  rp->setup_policy(clear_all_softrefs);
  rp->process_discovered_references(&GenMarkSweep::is_alive,
                                    &GenMarkSweep::keep_alive,
                                    &GenMarkSweep::follow_stack_closure,
                                    NULL);

  // Follow system dictionary roots and unload classes
  bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
  assert(GenMarkSweep::_marking_stack.is_empty(),
         "stack should be empty by now");

  // Follow code cache roots (has to be done after system dictionary,
  // assumes all live klasses are marked)
  CodeCache::do_unloading(&GenMarkSweep::is_alive,
                                   &GenMarkSweep::keep_alive,
                                   purged_class);
  GenMarkSweep::follow_stack();

  // Update subklass/sibling/implementor links of live klasses
  GenMarkSweep::follow_weak_klass_links();
  assert(GenMarkSweep::_marking_stack.is_empty(),
         "stack should be empty by now");

  // Visit memoized MDO's and clear any unmarked weak refs
  GenMarkSweep::follow_mdo_weak_refs();
  assert(GenMarkSweep::_marking_stack.is_empty(), "just drained");


  // Visit interned string tables and delete unmarked oops
  StringTable::unlink(&GenMarkSweep::is_alive);
  // Clean up unreferenced symbols in symbol table.
  SymbolTable::unlink();

  assert(GenMarkSweep::_marking_stack.is_empty(),
         "stack should be empty by now");

  if (VerifyDuringGC) {
    HandleMark hm;  // handle scope
    COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
    gclog_or_tty->print(" VerifyDuringGC:(full)[Verifying ");
    Universe::heap()->prepare_for_verify();
    // Note: we can verify only the heap here. When an object is
    // marked, the previous value of the mark word (including
    // identity hash values, ages, etc) is preserved, and the mark
    // word is set to markOop::marked_value - effectively removing
    // any hash values from the mark word. These hash values are
    // used when verifying the dictionaries and so removing them
    // from the mark word can make verification of the dictionaries
    // fail. At the end of the GC, the orginal mark word values
    // (including hash values) are restored to the appropriate
    // objects.
    Universe::heap()->verify(/* allow dirty */ true,
                             /* silent      */ false,
                             /* option      */ VerifyOption_G1UseMarkWord);

    G1CollectedHeap* g1h = G1CollectedHeap::heap();
    gclog_or_tty->print_cr("]");
  }
}

class G1PrepareCompactClosure: public HeapRegionClosure {
  G1CollectedHeap* _g1h;
  ModRefBarrierSet* _mrbs;
  CompactPoint _cp;
  HumongousRegionSet _humongous_proxy_set;

  void free_humongous_region(HeapRegion* hr) {
    HeapWord* end = hr->end();
    size_t dummy_pre_used;
    FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep");

    assert(hr->startsHumongous(),
           "Only the start of a humongous region should be freed.");
    _g1h->free_humongous_region(hr, &dummy_pre_used, &dummy_free_list,
                                &_humongous_proxy_set, false /* par */);
    hr->prepare_for_compaction(&_cp);
    // Also clear the part of the card table that will be unused after
    // compaction.
    _mrbs->clear(MemRegion(hr->compaction_top(), end));
    dummy_free_list.remove_all();
  }

public:
  G1PrepareCompactClosure(CompactibleSpace* cs)
  : _g1h(G1CollectedHeap::heap()),
    _mrbs(G1CollectedHeap::heap()->mr_bs()),
    _cp(NULL, cs, cs->initialize_threshold()),
    _humongous_proxy_set("G1MarkSweep Humongous Proxy Set") { }

  void update_sets() {
    // We'll recalculate total used bytes and recreate the free list
    // at the end of the GC, so no point in updating those values here.
    _g1h->update_sets_after_freeing_regions(0, /* pre_used */
                                            NULL, /* free_list */
                                            &_humongous_proxy_set,
                                            false /* par */);
  }

  bool doHeapRegion(HeapRegion* hr) {
    if (hr->isHumongous()) {
      if (hr->startsHumongous()) {
        oop obj = oop(hr->bottom());
        if (obj->is_gc_marked()) {
          obj->forward_to(obj);
        } else  {
          free_humongous_region(hr);
        }
      } else {
        assert(hr->continuesHumongous(), "Invalid humongous.");
      }
    } else {
      hr->prepare_for_compaction(&_cp);
      // Also clear the part of the card table that will be unused after
      // compaction.
      _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
    }
    return false;
  }
};

// Finds the first HeapRegion.
class FindFirstRegionClosure: public HeapRegionClosure {
  HeapRegion* _a_region;
public:
  FindFirstRegionClosure() : _a_region(NULL) {}
  bool doHeapRegion(HeapRegion* r) {
    _a_region = r;
    return true;
  }
  HeapRegion* result() { return _a_region; }
};

void G1MarkSweep::mark_sweep_phase2() {
  // Now all live objects are marked, compute the new object addresses.

  // It is imperative that we traverse perm_gen LAST. If dead space is
  // allowed a range of dead object may get overwritten by a dead int
  // array. If perm_gen is not traversed last a klassOop may get
  // overwritten. This is fine since it is dead, but if the class has dead
  // instances we have to skip them, and in order to find their size we
  // need the klassOop!
  //
  // It is not required that we traverse spaces in the same order in
  // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
  // tracking expects us to do so. See comment under phase4.

  G1CollectedHeap* g1h = G1CollectedHeap::heap();
  Generation* pg = g1h->perm_gen();

  EventMark m("2 compute new addresses");
  TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty);
  GenMarkSweep::trace("2");

  FindFirstRegionClosure cl;
  g1h->heap_region_iterate(&cl);
  HeapRegion *r = cl.result();
  CompactibleSpace* sp = r;
  if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) {
    sp = r->next_compaction_space();
  }

  G1PrepareCompactClosure blk(sp);
  g1h->heap_region_iterate(&blk);
  blk.update_sets();

  CompactPoint perm_cp(pg, NULL, NULL);
  pg->prepare_for_compaction(&perm_cp);
}

class G1AdjustPointersClosure: public HeapRegionClosure {
 public:
  bool doHeapRegion(HeapRegion* r) {
    if (r->isHumongous()) {
      if (r->startsHumongous()) {
        // We must adjust the pointers on the single H object.
        oop obj = oop(r->bottom());
        debug_only(GenMarkSweep::track_interior_pointers(obj));
        // point all the oops to the new location
        obj->adjust_pointers();
        debug_only(GenMarkSweep::check_interior_pointers());
      }
    } else {
      // This really ought to be "as_CompactibleSpace"...
      r->adjust_pointers();
    }
    return false;
  }
};

void G1MarkSweep::mark_sweep_phase3() {
  G1CollectedHeap* g1h = G1CollectedHeap::heap();
  Generation* pg = g1h->perm_gen();

  // Adjust the pointers to reflect the new locations
  EventMark m("3 adjust pointers");
  TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty);
  GenMarkSweep::trace("3");

  SharedHeap* sh = SharedHeap::heap();

  sh->process_strong_roots(true,  // activate StrongRootsScope
                           true,  // Collecting permanent generation.
                           SharedHeap::SO_AllClasses,
                           &GenMarkSweep::adjust_root_pointer_closure,
                           NULL,  // do not touch code cache here
                           &GenMarkSweep::adjust_pointer_closure);

  g1h->ref_processor()->weak_oops_do(&GenMarkSweep::adjust_root_pointer_closure);

  // Now adjust pointers in remaining weak roots.  (All of which should
  // have been cleared if they pointed to non-surviving objects.)
  g1h->g1_process_weak_roots(&GenMarkSweep::adjust_root_pointer_closure,
                             &GenMarkSweep::adjust_pointer_closure);

  GenMarkSweep::adjust_marks();

  G1AdjustPointersClosure blk;
  g1h->heap_region_iterate(&blk);
  pg->adjust_pointers();
}

class G1SpaceCompactClosure: public HeapRegionClosure {
public:
  G1SpaceCompactClosure() {}

  bool doHeapRegion(HeapRegion* hr) {
    if (hr->isHumongous()) {
      if (hr->startsHumongous()) {
        oop obj = oop(hr->bottom());
        if (obj->is_gc_marked()) {
          obj->init_mark();
        } else {
          assert(hr->is_empty(), "Should have been cleared in phase 2.");
        }
        hr->reset_during_compaction();
      }
    } else {
      hr->compact();
    }
    return false;
  }
};

void G1MarkSweep::mark_sweep_phase4() {
  // All pointers are now adjusted, move objects accordingly

  // It is imperative that we traverse perm_gen first in phase4. All
  // classes must be allocated earlier than their instances, and traversing
  // perm_gen first makes sure that all klassOops have moved to their new
  // location before any instance does a dispatch through it's klass!

  // The ValidateMarkSweep live oops tracking expects us to traverse spaces
  // in the same order in phase2, phase3 and phase4. We don't quite do that
  // here (perm_gen first rather than last), so we tell the validate code
  // to use a higher index (saved from phase2) when verifying perm_gen.
  G1CollectedHeap* g1h = G1CollectedHeap::heap();
  Generation* pg = g1h->perm_gen();

  EventMark m("4 compact heap");
  TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty);
  GenMarkSweep::trace("4");

  pg->compact();

  G1SpaceCompactClosure blk;
  g1h->heap_region_iterate(&blk);

}

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