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 *

 * This code is free software; you can redistribute it and/or modify it

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 * published by the Free Software Foundation.

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 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

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

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#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_interface/collectedHeap.inline.hpp"

#include "memory/genCollectedHeap.hpp"

#include "memory/genMarkSweep.hpp"

#include "memory/genOopClosures.inline.hpp"

#include "memory/generation.inline.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/fprofiler.hpp"

#include "runtime/handles.inline.hpp"

#include "runtime/synchronizer.hpp"

#include "runtime/thread.inline.hpp"

#include "runtime/vmThread.hpp"

#include "utilities/copy.hpp"

#include "utilities/events.hpp"

void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp,

  bool clear_all_softrefs) {

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

  GenCollectedHeap* gch = GenCollectedHeap::heap();

#ifdef ASSERT

  if (gch->collector_policy()->should_clear_all_soft_refs()) {

    assert(clear_all_softrefs, "Policy should have been checked earlier");

  }

#endif

  // hook up weak ref data so it can be used during Mark-Sweep

  assert(ref_processor() == NULL, "no stomping");

  assert(rp != NULL, "should be non-NULL");

  _ref_processor = rp;

  rp->setup_policy(clear_all_softrefs);

  // When collecting the permanent generation Method*s 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

  _total_invocations++;

  // Capture heap size before collection for printing.

  size_t gch_prev_used = gch->used();

  // Some of the card table updates below assume that the perm gen is

  // also being collected.

  assert(level == gch->n_gens() - 1,

         "All generations are being collected, ergo perm gen too.");

  // Capture used regions for each generation that will be

  // subject to collection, so that card table adjustments can

  // be made intelligently (see clear / invalidate further below).

  gch->save_used_regions(level);

  allocate_stacks();

  mark_sweep_phase1(level, clear_all_softrefs);

  mark_sweep_phase2();

  // Don't add any more derived pointers during phase3

  COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));

  COMPILER2_PRESENT(DerivedPointerTable::set_active(false));

  mark_sweep_phase3(level);

  mark_sweep_phase4();

  restore_marks();

  // Set saved marks for allocation profiler (and other things? -- dld)

  // (Should this be in general part?)

  gch->save_marks();

  deallocate_stacks();

  // If compaction completely evacuated all generations younger than this

  // one, then we can clear the card table.  Otherwise, we must invalidate

  // it (consider all cards dirty).  In the future, we might consider doing

  // compaction within generations only, and doing card-table sliding.

  bool all_empty = true;

  for (int i = 0; all_empty && i < level; i++) {

    Generation* g = gch->get_gen(i);

    all_empty = all_empty && gch->get_gen(i)->used() == 0;

  }

  GenRemSet* rs = gch->rem_set();

  // Clear/invalidate below make use of the "prev_used_regions" saved earlier.

  if (all_empty) {

    // We've evacuated all generations below us.

    Generation* g = gch->get_gen(level);

    rs->clear_into_younger(g);

  } else {

    // Invalidate the cards corresponding to the currently used

    // region and clear those corresponding to the evacuated region

    // of all generations just collected (i.e. level and younger).

    rs->invalidate_or_clear(gch->get_gen(level),

                            true /* younger */);

  }

  Threads::gc_epilogue();

  CodeCache::gc_epilogue();

  JvmtiExport::gc_epilogue();

  if (PrintGC && !PrintGCDetails) {

    gch->print_heap_change(gch_prev_used);

  }

  // refs processing: clean slate

  _ref_processor = NULL;

  // Update heap occupancy information which is used as

  // input to soft ref clearing policy at the next gc.

  Universe::update_heap_info_at_gc();

  // Update time of last gc for all generations we collected

  // (which curently is all the generations in the heap).

  // We need to use a monotonically non-deccreasing time in ms

  // or we will see time-warp warnings and os::javaTimeMillis()

  // does not guarantee monotonicity.

  jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;

  gch->update_time_of_last_gc(now);

}

void GenMarkSweep::allocate_stacks() {

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  // Scratch request on behalf of oldest generation; will do no

  // allocation.

  ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0);

  // $$$ To cut a corner, we'll only use the first scratch block, and then

  // revert to malloc.

  if (scratch != NULL) {

    _preserved_count_max =

      scratch->num_words * HeapWordSize / sizeof(PreservedMark);

  } else {

    _preserved_count_max = 0;

  }

  _preserved_marks = (PreservedMark*)scratch;

  _preserved_count = 0;

}

void GenMarkSweep::deallocate_stacks() {

  if (!UseG1GC) {

    GenCollectedHeap* gch = GenCollectedHeap::heap();

    gch->release_scratch();

  }

  _preserved_mark_stack.clear(true);

  _preserved_oop_stack.clear(true);

  _marking_stack.clear();

  _objarray_stack.clear(true);

}

void GenMarkSweep::mark_sweep_phase1(int level,

                                  bool clear_all_softrefs) {

  // Recursively traverse all live objects and mark them

  trace(" 1");

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  // Because follow_root_closure is created statically, cannot

  // use OopsInGenClosure constructor which takes a generation,

  // as the Universe has not been created when the static constructors

  // are run.

  follow_root_closure.set_orig_generation(gch->get_gen(level));

  // Need new claim bits before marking starts.

  ClassLoaderDataGraph::clear_claimed_marks();

  gch->gen_process_strong_roots(level,

                                false, // Younger gens are not roots.

                                true,  // activate StrongRootsScope

                                false, // not scavenging

                                SharedHeap::SO_SystemClasses,

                                &follow_root_closure,

                                true,   // walk code active on stacks

                                &follow_root_closure,

                                &follow_klass_closure);

  // Process reference objects found during marking

  {

    ref_processor()->setup_policy(clear_all_softrefs);

  }

  // This is the point where the entire marking should have completed.

  assert(_marking_stack.is_empty(), "Marking should have completed");

  // Unload classes and purge the SystemDictionary.

  bool purged_class = SystemDictionary::do_unloading(&is_alive);

  // Unload nmethods.

  CodeCache::do_unloading(&is_alive, purged_class);

  // Prune dead klasses from subklass/sibling/implementor lists.

  Klass::clean_weak_klass_links(&is_alive);

  // Delete entries for dead interned strings.

  StringTable::unlink(&is_alive);

  // Clean up unreferenced symbols in symbol table.

  SymbolTable::unlink();

}

void GenMarkSweep::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 Klass* 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 Klass*!

  //

  // 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.

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  trace("2");

  gch->prepare_for_compaction();

}

class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {

public:

  void do_generation(Generation* gen) {

    gen->adjust_pointers();

  }

};

void GenMarkSweep::mark_sweep_phase3(int level) {

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  // Adjust the pointers to reflect the new locations

  trace("3");

  // Need new claim bits for the pointer adjustment tracing.

  ClassLoaderDataGraph::clear_claimed_marks();

  // Because the closure below is created statically, we cannot

  // use OopsInGenClosure constructor which takes a generation,

  // as the Universe has not been created when the static constructors

  // are run.

  adjust_pointer_closure.set_orig_generation(gch->get_gen(level));

  gch->gen_process_strong_roots(level,

                                false, // Younger gens are not roots.

                                true,  // activate StrongRootsScope

                                false, // not scavenging

                                SharedHeap::SO_AllClasses,

                                &adjust_pointer_closure,

                                false, // do not walk code

                                &adjust_pointer_closure,

                                &adjust_klass_closure);

  // Now adjust pointers in remaining weak roots.  (All of which should

  // have been cleared if they pointed to non-surviving objects.)

  CodeBlobToOopClosure adjust_code_pointer_closure(&adjust_pointer_closure,

                                                   /*do_marking=*/ false);

  gch->gen_process_weak_roots(&adjust_pointer_closure,

                              &adjust_code_pointer_closure);

  adjust_marks();

  GenAdjustPointersClosure blk;

  gch->generation_iterate(&blk, true);

}

class GenCompactClosure: public GenCollectedHeap::GenClosure {

public:

  void do_generation(Generation* gen) {

    gen->compact();

  }

};

void GenMarkSweep::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 Klass*s 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.

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  trace("4");

  GenCompactClosure blk;

  gch->generation_iterate(&blk, true);

}