hotspot/src/share/vm/memory/genMarkSweep.cpp - platform/libcore - Git at Google

 /*
  * Copyright 2001-2007 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  * CA 95054 USA or visit www.sun.com if you need additional information or
  * have any questions.
  *
  */

 #include "incls/_precompiled.incl"
 #include "incls/_genMarkSweep.cpp.incl"

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

   // hook up weak ref data so it can be used during Mark-Sweep
   assert(ref_processor() == NULL, "no stomping");
   _ref_processor = rp;
   assert(rp != NULL, "should be non-NULL");

   TraceTime t1("Full GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);

   // 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.
   GenCollectedHeap* gch = GenCollectedHeap::heap();
   gch->perm_gen()->stat_record()->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, true /* perm */);

   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);

   VALIDATE_MARK_SWEEP_ONLY(
     if (ValidateMarkSweep) {
       guarantee(_root_refs_stack->length() == 0,
                 "should be empty by now");
     }
   )

   mark_sweep_phase4();

   VALIDATE_MARK_SWEEP_ONLY(
     if (ValidateMarkSweep) {
       guarantee(_live_oops->length() == _live_oops_moved_to->length(),
                 "should be the same size");
     }
   )

   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, true /* perm */);
   } 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 */,
                             true /* perm */);
   }

   Threads::gc_epilogue();
   CodeCache::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).
   gch->update_time_of_last_gc(os::javaTimeMillis());
 }

 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;
   _preserved_mark_stack = NULL;
   _preserved_oop_stack = NULL;

   _marking_stack       = new (ResourceObj::C_HEAP) GrowableArray<oop>(4000, true);

   int size = SystemDictionary::number_of_classes() * 2;
   _revisit_klass_stack = new (ResourceObj::C_HEAP) GrowableArray<Klass*>(size, true);

 #ifdef VALIDATE_MARK_SWEEP
   if (ValidateMarkSweep) {
     _root_refs_stack    = new (ResourceObj::C_HEAP) GrowableArray<oop*>(100, true);
     _other_refs_stack   = new (ResourceObj::C_HEAP) GrowableArray<oop*>(100, true);
     _adjusted_pointers  = new (ResourceObj::C_HEAP) GrowableArray<oop*>(100, true);
     _live_oops          = new (ResourceObj::C_HEAP) GrowableArray<oop>(100, true);
     _live_oops_moved_to = new (ResourceObj::C_HEAP) GrowableArray<oop>(100, true);
     _live_oops_size     = new (ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
   }
   if (RecordMarkSweepCompaction) {
     if (_cur_gc_live_oops == NULL) {
       _cur_gc_live_oops           = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
       _cur_gc_live_oops_moved_to  = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
       _cur_gc_live_oops_size      = new(ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
       _last_gc_live_oops          = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
       _last_gc_live_oops_moved_to = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
       _last_gc_live_oops_size     = new(ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
     } else {
       _cur_gc_live_oops->clear();
       _cur_gc_live_oops_moved_to->clear();
       _cur_gc_live_oops_size->clear();
     }
   }
 #endif
 }


 void GenMarkSweep::deallocate_stacks() {
   if (_preserved_oop_stack) {
     delete _preserved_mark_stack;
     _preserved_mark_stack = NULL;
     delete _preserved_oop_stack;
     _preserved_oop_stack = NULL;
   }

   delete _marking_stack;
   delete _revisit_klass_stack;

 #ifdef VALIDATE_MARK_SWEEP
   if (ValidateMarkSweep) {
     delete _root_refs_stack;
     delete _other_refs_stack;
     delete _adjusted_pointers;
     delete _live_oops;
     delete _live_oops_size;
     delete _live_oops_moved_to;
     _live_oops_index = 0;
     _live_oops_index_at_perm = 0;
   }
 #endif
 }

 void GenMarkSweep::mark_sweep_phase1(int level,
                                   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);
   trace(" 1");

   VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

   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));

   gch->gen_process_strong_roots(level,
                                 false, // Younger gens are not roots.
                                 true,  // Collecting permanent generation.
                                 SharedHeap::SO_SystemClasses,
                                 &follow_root_closure, &follow_root_closure);

   // Process reference objects found during marking
   {
     ReferencePolicy *soft_ref_policy;
     if (clear_all_softrefs) {
       soft_ref_policy = new AlwaysClearPolicy();
     } else {
 #ifdef COMPILER2
       soft_ref_policy = new LRUMaxHeapPolicy();
 #else
       soft_ref_policy = new LRUCurrentHeapPolicy();
 #endif // COMPILER2
     }
     assert(soft_ref_policy != NULL,"No soft reference policy");
     ref_processor()->process_discovered_references(
       soft_ref_policy, &is_alive, &keep_alive,
       &follow_stack_closure, NULL);
   }

   // Follow system dictionary roots and unload classes
   bool purged_class = SystemDictionary::do_unloading(&is_alive);

   // Follow code cache roots
   CodeCache::do_unloading(&is_alive, &keep_alive, purged_class);
   follow_stack(); // Flush marking stack

   // Update subklass/sibling/implementor links of live klasses
   follow_weak_klass_links();
   assert(_marking_stack->is_empty(), "just drained");

   // Visit symbol and interned string tables and delete unmarked oops
   SymbolTable::unlink(&is_alive);
   StringTable::unlink(&is_alive);

   assert(_marking_stack->is_empty(), "stack should be empty by now");
 }


 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 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.

   GenCollectedHeap* gch = GenCollectedHeap::heap();
   Generation* pg = gch->perm_gen();

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

   VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

   gch->prepare_for_compaction();

   VALIDATE_MARK_SWEEP_ONLY(_live_oops_index_at_perm = _live_oops_index);
   CompactPoint perm_cp(pg, NULL, NULL);
   pg->prepare_for_compaction(&perm_cp);
 }

 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();
   Generation* pg = gch->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);
   trace("3");

   VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

   // Needs to be done before the system dictionary is adjusted.
   pg->pre_adjust_pointers();

   // Because the two closures below are created statically, cannot
   // use OopsInGenClosure constructor which takes a generation,
   // as the Universe has not been created when the static constructors
   // are run.
   adjust_root_pointer_closure.set_orig_generation(gch->get_gen(level));
   adjust_pointer_closure.set_orig_generation(gch->get_gen(level));

   gch->gen_process_strong_roots(level,
                                 false, // Younger gens are not roots.
                                 true,  // Collecting permanent generation.
                                 SharedHeap::SO_AllClasses,
                                 &adjust_root_pointer_closure,
                                 &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.)
   gch->gen_process_weak_roots(&adjust_root_pointer_closure,
                               &adjust_pointer_closure);

   adjust_marks();
   GenAdjustPointersClosure blk;
   gch->generation_iterate(&blk, true);
   pg->adjust_pointers();
 }

 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 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.
   GenCollectedHeap* gch = GenCollectedHeap::heap();
   Generation* pg = gch->perm_gen();

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

   VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(true));

   pg->compact();

   VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

   GenCompactClosure blk;
   gch->generation_iterate(&blk, true);

   VALIDATE_MARK_SWEEP_ONLY(compaction_complete());

   pg->post_compact(); // Shared spaces verification.
 }
	/*
	* Copyright 2001-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
	* CA 95054 USA or visit www.sun.com if you need additional information or
	* have any questions.
	*
	*/

	#include "incls/_precompiled.incl"
	#include "incls/_genMarkSweep.cpp.incl"

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

	// hook up weak ref data so it can be used during Mark-Sweep
	assert(ref_processor() == NULL, "no stomping");
	_ref_processor = rp;
	assert(rp != NULL, "should be non-NULL");

	TraceTime t1("Full GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);

	// 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.
	GenCollectedHeap* gch = GenCollectedHeap::heap();
	gch->perm_gen()->stat_record()->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, true /* perm */);

	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);

	VALIDATE_MARK_SWEEP_ONLY(
	if (ValidateMarkSweep) {
	guarantee(_root_refs_stack->length() == 0,
	"should be empty by now");
	}
	)

	mark_sweep_phase4();

	VALIDATE_MARK_SWEEP_ONLY(
	if (ValidateMarkSweep) {
	guarantee(_live_oops->length() == _live_oops_moved_to->length(),
	"should be the same size");
	}
	)

	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, true /* perm */);
	} 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 */,
	true /* perm */);
	}

	Threads::gc_epilogue();
	CodeCache::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).
	gch->update_time_of_last_gc(os::javaTimeMillis());
	}

	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;
	_preserved_mark_stack = NULL;
	_preserved_oop_stack = NULL;

	_marking_stack = new (ResourceObj::C_HEAP) GrowableArray<oop>(4000, true);

	int size = SystemDictionary::number_of_classes() * 2;
	_revisit_klass_stack = new (ResourceObj::C_HEAP) GrowableArray<Klass*>(size, true);

	#ifdef VALIDATE_MARK_SWEEP
	if (ValidateMarkSweep) {
	_root_refs_stack = new (ResourceObj::C_HEAP) GrowableArray<oop*>(100, true);
	_other_refs_stack = new (ResourceObj::C_HEAP) GrowableArray<oop*>(100, true);
	_adjusted_pointers = new (ResourceObj::C_HEAP) GrowableArray<oop*>(100, true);
	_live_oops = new (ResourceObj::C_HEAP) GrowableArray<oop>(100, true);
	_live_oops_moved_to = new (ResourceObj::C_HEAP) GrowableArray<oop>(100, true);
	_live_oops_size = new (ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
	}
	if (RecordMarkSweepCompaction) {
	if (_cur_gc_live_oops == NULL) {
	_cur_gc_live_oops = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
	_cur_gc_live_oops_moved_to = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
	_cur_gc_live_oops_size = new(ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
	_last_gc_live_oops = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
	_last_gc_live_oops_moved_to = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
	_last_gc_live_oops_size = new(ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
	} else {
	_cur_gc_live_oops->clear();
	_cur_gc_live_oops_moved_to->clear();
	_cur_gc_live_oops_size->clear();
	}
	}
	#endif
	}


	void GenMarkSweep::deallocate_stacks() {
	if (_preserved_oop_stack) {
	delete _preserved_mark_stack;
	_preserved_mark_stack = NULL;
	delete _preserved_oop_stack;
	_preserved_oop_stack = NULL;
	}

	delete _marking_stack;
	delete _revisit_klass_stack;

	#ifdef VALIDATE_MARK_SWEEP
	if (ValidateMarkSweep) {
	delete _root_refs_stack;
	delete _other_refs_stack;
	delete _adjusted_pointers;
	delete _live_oops;
	delete _live_oops_size;
	delete _live_oops_moved_to;
	_live_oops_index = 0;
	_live_oops_index_at_perm = 0;
	}
	#endif
	}

	void GenMarkSweep::mark_sweep_phase1(int level,
	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);
	trace(" 1");

	VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

	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));

	gch->gen_process_strong_roots(level,
	false, // Younger gens are not roots.
	true, // Collecting permanent generation.
	SharedHeap::SO_SystemClasses,
	&follow_root_closure, &follow_root_closure);

	// Process reference objects found during marking
	{
	ReferencePolicy *soft_ref_policy;
	if (clear_all_softrefs) {
	soft_ref_policy = new AlwaysClearPolicy();
	} else {
	#ifdef COMPILER2
	soft_ref_policy = new LRUMaxHeapPolicy();
	#else
	soft_ref_policy = new LRUCurrentHeapPolicy();
	#endif // COMPILER2
	}
	assert(soft_ref_policy != NULL,"No soft reference policy");
	ref_processor()->process_discovered_references(
	soft_ref_policy, &is_alive, &keep_alive,
	&follow_stack_closure, NULL);
	}

	// Follow system dictionary roots and unload classes
	bool purged_class = SystemDictionary::do_unloading(&is_alive);

	// Follow code cache roots
	CodeCache::do_unloading(&is_alive, &keep_alive, purged_class);
	follow_stack(); // Flush marking stack

	// Update subklass/sibling/implementor links of live klasses
	follow_weak_klass_links();
	assert(_marking_stack->is_empty(), "just drained");

	// Visit symbol and interned string tables and delete unmarked oops
	SymbolTable::unlink(&is_alive);
	StringTable::unlink(&is_alive);

	assert(_marking_stack->is_empty(), "stack should be empty by now");
	}


	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 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.

	GenCollectedHeap* gch = GenCollectedHeap::heap();
	Generation* pg = gch->perm_gen();

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

	VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

	gch->prepare_for_compaction();

	VALIDATE_MARK_SWEEP_ONLY(_live_oops_index_at_perm = _live_oops_index);
	CompactPoint perm_cp(pg, NULL, NULL);
	pg->prepare_for_compaction(&perm_cp);
	}

	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();
	Generation* pg = gch->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);
	trace("3");

	VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

	// Needs to be done before the system dictionary is adjusted.
	pg->pre_adjust_pointers();

	// Because the two closures below are created statically, cannot
	// use OopsInGenClosure constructor which takes a generation,
	// as the Universe has not been created when the static constructors
	// are run.
	adjust_root_pointer_closure.set_orig_generation(gch->get_gen(level));
	adjust_pointer_closure.set_orig_generation(gch->get_gen(level));

	gch->gen_process_strong_roots(level,
	false, // Younger gens are not roots.
	true, // Collecting permanent generation.
	SharedHeap::SO_AllClasses,
	&adjust_root_pointer_closure,
	&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.)
	gch->gen_process_weak_roots(&adjust_root_pointer_closure,
	&adjust_pointer_closure);

	adjust_marks();
	GenAdjustPointersClosure blk;
	gch->generation_iterate(&blk, true);
	pg->adjust_pointers();
	}

	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 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.
	GenCollectedHeap* gch = GenCollectedHeap::heap();
	Generation* pg = gch->perm_gen();

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

	VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(true));

	pg->compact();

	VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

	GenCompactClosure blk;
	gch->generation_iterate(&blk, true);

	VALIDATE_MARK_SWEEP_ONLY(compaction_complete());

	pg->post_compact(); // Shared spaces verification.
	}