Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright 2000-2008 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,

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 # include "incls/_precompiled.incl"

 # include "incls/_genCollectedHeap.cpp.incl"

 GenCollectedHeap* GenCollectedHeap::_gch;

 NOT_PRODUCT(size_t GenCollectedHeap::_skip_header_HeapWords = 0;)

 // The set of potentially parallel tasks in strong root scanning.

 enum GCH_process_strong_roots_tasks {

   // We probably want to parallelize both of these internally, but for now...

   GCH_PS_younger_gens,

   // Leave this one last.

   GCH_PS_NumElements

 };

 GenCollectedHeap::GenCollectedHeap(GenCollectorPolicy *policy) :

   SharedHeap(policy),

   _gen_policy(policy),

   _gen_process_strong_tasks(new SubTasksDone(GCH_PS_NumElements)),

   _full_collections_completed(0)

 {

   if (_gen_process_strong_tasks == NULL ||

       !_gen_process_strong_tasks->valid()) {

     vm_exit_during_initialization("Failed necessary allocation.");

   }

   assert(policy != NULL, "Sanity check");

   _preloading_shared_classes = false;

 }

 jint GenCollectedHeap::initialize() {

   int i;

   _n_gens = gen_policy()->number_of_generations();

   // While there are no constraints in the GC code that HeapWordSize

   // be any particular value, there are multiple other areas in the

   // system which believe this to be true (e.g. oop->object_size in some

   // cases incorrectly returns the size in wordSize units rather than

   // HeapWordSize).

   guarantee(HeapWordSize == wordSize, "HeapWordSize must equal wordSize");

   // The heap must be at least as aligned as generations.

   size_t alignment = Generation::GenGrain;

   _gen_specs = gen_policy()->generations();

   PermanentGenerationSpec *perm_gen_spec =

                                 collector_policy()->permanent_generation();

   // Make sure the sizes are all aligned.

   for (i = 0; i < _n_gens; i++) {

     _gen_specs[i]->align(alignment);

   }

   perm_gen_spec->align(alignment);

   // If we are dumping the heap, then allocate a wasted block of address

   // space in order to push the heap to a lower address.  This extra

   // address range allows for other (or larger) libraries to be loaded

   // without them occupying the space required for the shared spaces.

   if (DumpSharedSpaces) {

     uintx reserved = 0;

     uintx block_size = 64*1024*1024;

     while (reserved < SharedDummyBlockSize) {

       char* dummy = os::reserve_memory(block_size);

       reserved += block_size;

     }

   }

   // Allocate space for the heap.

   char* heap_address;

   size_t total_reserved = 0;

   int n_covered_regions = 0;

   ReservedSpace heap_rs(0);

   heap_address = allocate(alignment, perm_gen_spec, &total_reserved,

                           &n_covered_regions, &heap_rs);

   if (UseSharedSpaces) {

     if (!heap_rs.is_reserved() || heap_address != heap_rs.base()) {

       if (heap_rs.is_reserved()) {

         heap_rs.release();

       }

       FileMapInfo* mapinfo = FileMapInfo::current_info();

       mapinfo->fail_continue("Unable to reserve shared region.");

       allocate(alignment, perm_gen_spec, &total_reserved, &n_covered_regions,

                &heap_rs);

     }

   }

   if (!heap_rs.is_reserved()) {

     vm_shutdown_during_initialization(

       "Could not reserve enough space for object heap");

     return JNI_ENOMEM;

   }

   _reserved = MemRegion((HeapWord*)heap_rs.base(),

                         (HeapWord*)(heap_rs.base() + heap_rs.size()));

   // It is important to do this in a way such that concurrent readers can't

   // temporarily think somethings in the heap.  (Seen this happen in asserts.)

   _reserved.set_word_size(0);

   _reserved.set_start((HeapWord*)heap_rs.base());

   size_t actual_heap_size = heap_rs.size() - perm_gen_spec->misc_data_size()

                                            - perm_gen_spec->misc_code_size();

   _reserved.set_end((HeapWord*)(heap_rs.base() + actual_heap_size));

   _rem_set = collector_policy()->create_rem_set(_reserved, n_covered_regions);

   set_barrier_set(rem_set()->bs());

   _gch = this;

   for (i = 0; i < _n_gens; i++) {

     ReservedSpace this_rs = heap_rs.first_part(_gen_specs[i]->max_size(),

                                               UseSharedSpaces, UseSharedSpaces);

     _gens[i] = _gen_specs[i]->init(this_rs, i, rem_set());

     heap_rs = heap_rs.last_part(_gen_specs[i]->max_size());

   }

   _perm_gen = perm_gen_spec->init(heap_rs, PermSize, rem_set());

   clear_incremental_collection_will_fail();

   clear_last_incremental_collection_failed();

 #ifndef SERIALGC

   // If we are running CMS, create the collector responsible

   // for collecting the CMS generations.

   if (collector_policy()->is_concurrent_mark_sweep_policy()) {

     bool success = create_cms_collector();

     if (!success) return JNI_ENOMEM;

   }

 #endif // SERIALGC

   return JNI_OK;

 }

 char* GenCollectedHeap::allocate(size_t alignment,

                                  PermanentGenerationSpec* perm_gen_spec,

                                  size_t* _total_reserved,

                                  int* _n_covered_regions,

                                  ReservedSpace* heap_rs){

   const char overflow_msg[] = "The size of the object heap + VM data exceeds "

     "the maximum representable size";

   // Now figure out the total size.

   size_t total_reserved = 0;

   int n_covered_regions = 0;

   const size_t pageSize = UseLargePages ?

       os::large_page_size() : os::vm_page_size();

   for (int i = 0; i < _n_gens; i++) {

     total_reserved += _gen_specs[i]->max_size();

     if (total_reserved < _gen_specs[i]->max_size()) {

       vm_exit_during_initialization(overflow_msg);

     }

     n_covered_regions += _gen_specs[i]->n_covered_regions();

   }

   assert(total_reserved % pageSize == 0, "Gen size");

   total_reserved += perm_gen_spec->max_size();

   assert(total_reserved % pageSize == 0, "Perm Gen size");

   if (total_reserved < perm_gen_spec->max_size()) {

     vm_exit_during_initialization(overflow_msg);

   }

   n_covered_regions += perm_gen_spec->n_covered_regions();

   // Add the size of the data area which shares the same reserved area

   // as the heap, but which is not actually part of the heap.

   size_t s = perm_gen_spec->misc_data_size() + perm_gen_spec->misc_code_size();

   total_reserved += s;

   if (total_reserved < s) {

     vm_exit_during_initialization(overflow_msg);

   }

   if (UseLargePages) {

     assert(total_reserved != 0, "total_reserved cannot be 0");

     total_reserved = round_to(total_reserved, os::large_page_size());

     if (total_reserved < os::large_page_size()) {

       vm_exit_during_initialization(overflow_msg);

     }

   }

   // Calculate the address at which the heap must reside in order for

   // the shared data to be at the required address.

   char* heap_address;

   if (UseSharedSpaces) {

     // Calculate the address of the first word beyond the heap.

     FileMapInfo* mapinfo = FileMapInfo::current_info();

     int lr = CompactingPermGenGen::n_regions - 1;

     size_t capacity = align_size_up(mapinfo->space_capacity(lr), alignment);

     heap_address = mapinfo->region_base(lr) + capacity;

     // Calculate the address of the first word of the heap.

     heap_address -= total_reserved;

   } else {

     heap_address = NULL;  // any address will do.

     if (UseCompressedOops) {

       heap_address = Universe::preferred_heap_base(total_reserved, Universe::UnscaledNarrowOop);

       *_total_reserved = total_reserved;

       *_n_covered_regions = n_covered_regions;

       *heap_rs = ReservedHeapSpace(total_reserved, alignment,

                                    UseLargePages, heap_address);

       if (heap_address != NULL && !heap_rs->is_reserved()) {

         // Failed to reserve at specified address - the requested memory

         // region is taken already, for example, by 'java' launcher.

         // Try again to reserver heap higher.

         heap_address = Universe::preferred_heap_base(total_reserved, Universe::ZeroBasedNarrowOop);

         *heap_rs = ReservedHeapSpace(total_reserved, alignment,

                                      UseLargePages, heap_address);

         if (heap_address != NULL && !heap_rs->is_reserved()) {

           // Failed to reserve at specified address again - give up.

           heap_address = Universe::preferred_heap_base(total_reserved, Universe::HeapBasedNarrowOop);

           assert(heap_address == NULL, "");

           *heap_rs = ReservedHeapSpace(total_reserved, alignment,

                                        UseLargePages, heap_address);

         }

       }

       return heap_address;

     }

   }

   *_total_reserved = total_reserved;

   *_n_covered_regions = n_covered_regions;

   *heap_rs = ReservedHeapSpace(total_reserved, alignment,

                                UseLargePages, heap_address);

   return heap_address;

 }

 void GenCollectedHeap::post_initialize() {

   SharedHeap::post_initialize();

   TwoGenerationCollectorPolicy *policy =

     (TwoGenerationCollectorPolicy *)collector_policy();

   guarantee(policy->is_two_generation_policy(), "Illegal policy type");

   DefNewGeneration* def_new_gen = (DefNewGeneration*) get_gen(0);

   assert(def_new_gen->kind() == Generation::DefNew ||

          def_new_gen->kind() == Generation::ParNew ||

          def_new_gen->kind() == Generation::ASParNew,

          "Wrong generation kind");

   Generation* old_gen = get_gen(1);

   assert(old_gen->kind() == Generation::ConcurrentMarkSweep ||

          old_gen->kind() == Generation::ASConcurrentMarkSweep ||

          old_gen->kind() == Generation::MarkSweepCompact,

     "Wrong generation kind");

   policy->initialize_size_policy(def_new_gen->eden()->capacity(),

                                  old_gen->capacity(),

                                  def_new_gen->from()->capacity());

   policy->initialize_gc_policy_counters();

 }

 void GenCollectedHeap::ref_processing_init() {

   SharedHeap::ref_processing_init();

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->ref_processor_init();

   }

 }

 size_t GenCollectedHeap::capacity() const {

   size_t res = 0;

   for (int i = 0; i < _n_gens; i++) {

     res += _gens[i]->capacity();

   }

   return res;

 }

 size_t GenCollectedHeap::used() const {

   size_t res = 0;

   for (int i = 0; i < _n_gens; i++) {

     res += _gens[i]->used();

   }

   return res;

 }

 // Save the "used_region" for generations level and lower,

 // and, if perm is true, for perm gen.

 void GenCollectedHeap::save_used_regions(int level, bool perm) {

   assert(level < _n_gens, "Illegal level parameter");

   for (int i = level; i >= 0; i--) {

     _gens[i]->save_used_region();

   }

   if (perm) {

     perm_gen()->save_used_region();

   }

 }

 size_t GenCollectedHeap::max_capacity() const {

   size_t res = 0;

   for (int i = 0; i < _n_gens; i++) {

     res += _gens[i]->max_capacity();

   }

   return res;

 }

 // Update the _full_collections_completed counter

 // at the end of a stop-world full GC.

 unsigned int GenCollectedHeap::update_full_collections_completed() {

   MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);

   assert(_full_collections_completed <= _total_full_collections,

          "Can't complete more collections than were started");

   _full_collections_completed = _total_full_collections;

   ml.notify_all();

   return _full_collections_completed;

 }

 // Update the _full_collections_completed counter, as appropriate,

 // at the end of a concurrent GC cycle. Note the conditional update

 // below to allow this method to be called by a concurrent collector

 // without synchronizing in any manner with the VM thread (which

 // may already have initiated a STW full collection "concurrently").

 unsigned int GenCollectedHeap::update_full_collections_completed(unsigned int count) {

   MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);

   assert((_full_collections_completed <= _total_full_collections) &&

          (count <= _total_full_collections),

          "Can't complete more collections than were started");

   if (count > _full_collections_completed) {

     _full_collections_completed = count;

     ml.notify_all();

   }

   return _full_collections_completed;

 }

 #ifndef PRODUCT

 // Override of memory state checking method in CollectedHeap:

 // Some collectors (CMS for example) can't have badHeapWordVal written

 // in the first two words of an object. (For instance , in the case of

 // CMS these words hold state used to synchronize between certain

 // (concurrent) GC steps and direct allocating mutators.)

 // The skip_header_HeapWords() method below, allows us to skip

 // over the requisite number of HeapWord's. Note that (for

 // generational collectors) this means that those many words are

 // skipped in each object, irrespective of the generation in which

 // that object lives. The resultant loss of precision seems to be

 // harmless and the pain of avoiding that imprecision appears somewhat

 // higher than we are prepared to pay for such rudimentary debugging

 // support.

 void GenCollectedHeap::check_for_non_bad_heap_word_value(HeapWord* addr,

                                                          size_t size) {

   if (CheckMemoryInitialization && ZapUnusedHeapArea) {

     // We are asked to check a size in HeapWords,

     // but the memory is mangled in juint words.

     juint* start = (juint*) (addr + skip_header_HeapWords());

     juint* end   = (juint*) (addr + size);

     for (juint* slot = start; slot < end; slot += 1) {

       assert(*slot == badHeapWordVal,

              "Found non badHeapWordValue in pre-allocation check");

     }

   }

 }

 #endif

 HeapWord* GenCollectedHeap::attempt_allocation(size_t size,

                                                bool is_tlab,

                                                bool first_only) {

   HeapWord* res;

   for (int i = 0; i < _n_gens; i++) {

     if (_gens[i]->should_allocate(size, is_tlab)) {

       res = _gens[i]->allocate(size, is_tlab);

       if (res != NULL) return res;

       else if (first_only) break;

     }

   }

   // Otherwise...

   return NULL;

 }

 HeapWord* GenCollectedHeap::mem_allocate(size_t size,

                                          bool is_large_noref,

                                          bool is_tlab,

                                          bool* gc_overhead_limit_was_exceeded) {

   return collector_policy()->mem_allocate_work(size,

                                                is_tlab,

                                                gc_overhead_limit_was_exceeded);

 }

 bool GenCollectedHeap::must_clear_all_soft_refs() {

   return _gc_cause == GCCause::_last_ditch_collection;

 }

 bool GenCollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) {

   return (cause == GCCause::_java_lang_system_gc ||

           cause == GCCause::_gc_locker) &&

          UseConcMarkSweepGC && ExplicitGCInvokesConcurrent;

 }

 void GenCollectedHeap::do_collection(bool  full,

                                      bool   clear_all_soft_refs,

                                      size_t size,

                                      bool   is_tlab,

                                      int    max_level) {

   bool prepared_for_verification = false;

   ResourceMark rm;

   DEBUG_ONLY(Thread* my_thread = Thread::current();)

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

   assert(my_thread->is_VM_thread() ||

          my_thread->is_ConcurrentGC_thread(),

          "incorrect thread type capability");

   assert(Heap_lock->is_locked(), "the requesting thread should have the Heap_lock");

   guarantee(!is_gc_active(), "collection is not reentrant");

   assert(max_level < n_gens(), "sanity check");

   if (GC_locker::check_active_before_gc()) {

     return; // GC is disabled (e.g. JNI GetXXXCritical operation)

   }

   const size_t perm_prev_used = perm_gen()->used();

   if (PrintHeapAtGC) {

     Universe::print_heap_before_gc();

     if (Verbose) {

       gclog_or_tty->print_cr("GC Cause: %s", GCCause::to_string(gc_cause()));

     }

   }

   {

     FlagSetting fl(_is_gc_active, true);

     bool complete = full && (max_level == (n_gens()-1));

     const char* gc_cause_str = "GC ";

     if (complete) {

       GCCause::Cause cause = gc_cause();

       if (cause == GCCause::_java_lang_system_gc) {

         gc_cause_str = "Full GC (System) ";

       } else {

         gc_cause_str = "Full GC ";

       }

     }

     gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);

     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);

     TraceTime t(gc_cause_str, PrintGCDetails, false, gclog_or_tty);

     gc_prologue(complete);

     increment_total_collections(complete);

     size_t gch_prev_used = used();

     int starting_level = 0;

     if (full) {

       // Search for the oldest generation which will collect all younger

       // generations, and start collection loop there.

       for (int i = max_level; i >= 0; i--) {

         if (_gens[i]->full_collects_younger_generations()) {

           starting_level = i;

           break;

         }

       }

     }

     bool must_restore_marks_for_biased_locking = false;

     int max_level_collected = starting_level;

     for (int i = starting_level; i <= max_level; i++) {

       if (_gens[i]->should_collect(full, size, is_tlab)) {

         if (i == n_gens() - 1) {  // a major collection is to happen

           pre_full_gc_dump();    // do any pre full gc dumps

         }

         // Timer for individual generations. Last argument is false: no CR

         TraceTime t1(_gens[i]->short_name(), PrintGCDetails, false, gclog_or_tty);

         TraceCollectorStats tcs(_gens[i]->counters());

         TraceMemoryManagerStats tmms(_gens[i]->kind());

         size_t prev_used = _gens[i]->used();

         _gens[i]->stat_record()->invocations++;

         _gens[i]->stat_record()->accumulated_time.start();

         // Must be done anew before each collection because

         // a previous collection will do mangling and will

         // change top of some spaces.

         record_gen_tops_before_GC();

         if (PrintGC && Verbose) {

           gclog_or_tty->print("level=%d invoke=%d size=" SIZE_FORMAT,

                      i,

                      _gens[i]->stat_record()->invocations,

                      size*HeapWordSize);

         }

         if (VerifyBeforeGC && i >= VerifyGCLevel &&

             total_collections() >= VerifyGCStartAt) {

           HandleMark hm;  // Discard invalid handles created during verification

           if (!prepared_for_verification) {

             prepare_for_verify();

             prepared_for_verification = true;

           }

           gclog_or_tty->print(" VerifyBeforeGC:");

           Universe::verify(true);

         }

         COMPILER2_PRESENT(DerivedPointerTable::clear());

         if (!must_restore_marks_for_biased_locking &&

             _gens[i]->performs_in_place_marking()) {

           // We perform this mark word preservation work lazily

           // because it's only at this point that we know whether we

           // absolutely have to do it; we want to avoid doing it for

           // scavenge-only collections where it's unnecessary

           must_restore_marks_for_biased_locking = true;

           BiasedLocking::preserve_marks();

         }

         // Do collection work

         {

           // Note on ref discovery: For what appear to be historical reasons,

           // GCH enables and disabled (by enqueing) refs discovery.

           // In the future this should be moved into the generation's

           // collect method so that ref discovery and enqueueing concerns

           // are local to a generation. The collect method could return

           // an appropriate indication in the case that notification on

           // the ref lock was needed. This will make the treatment of

           // weak refs more uniform (and indeed remove such concerns

           // from GCH). XXX

           HandleMark hm;  // Discard invalid handles created during gc

           save_marks();   // save marks for all gens

           // We want to discover references, but not process them yet.

           // This mode is disabled in process_discovered_references if the

           // generation does some collection work, or in

           // enqueue_discovered_references if the generation returns

           // without doing any work.

           ReferenceProcessor* rp = _gens[i]->ref_processor();

           // If the discovery of ("weak") refs in this generation is

           // atomic wrt other collectors in this configuration, we

           // are guaranteed to have empty discovered ref lists.

           if (rp->discovery_is_atomic()) {

             rp->verify_no_references_recorded();

             rp->enable_discovery();

             rp->setup_policy(clear_all_soft_refs);

           } else {

             // collect() below will enable discovery as appropriate

           }

           _gens[i]->collect(full, clear_all_soft_refs, size, is_tlab);

           if (!rp->enqueuing_is_done()) {

             rp->enqueue_discovered_references();

           } else {

             rp->set_enqueuing_is_done(false);

           }

           rp->verify_no_references_recorded();

         }

         max_level_collected = i;

         // Determine if allocation request was met.

         if (size > 0) {

           if (!is_tlab || _gens[i]->supports_tlab_allocation()) {

             if (size*HeapWordSize <= _gens[i]->unsafe_max_alloc_nogc()) {

               size = 0;

             }

           }

         }

         COMPILER2_PRESENT(DerivedPointerTable::update_pointers());

         _gens[i]->stat_record()->accumulated_time.stop();

         update_gc_stats(i, full);

         if (VerifyAfterGC && i >= VerifyGCLevel &&

             total_collections() >= VerifyGCStartAt) {

           HandleMark hm;  // Discard invalid handles created during verification

           gclog_or_tty->print(" VerifyAfterGC:");

           Universe::verify(false);

         }

         if (PrintGCDetails) {

           gclog_or_tty->print(":");

           _gens[i]->print_heap_change(prev_used);

         }

       }

     }

     // Update "complete" boolean wrt what actually transpired --

     // for instance, a promotion failure could have led to

     // a whole heap collection.

     complete = complete || (max_level_collected == n_gens() - 1);

     if (complete) { // We did a "major" collection

       post_full_gc_dump();   // do any post full gc dumps

     }

     if (PrintGCDetails) {

       print_heap_change(gch_prev_used);

       // Print perm gen info for full GC with PrintGCDetails flag.

       if (complete) {

         print_perm_heap_change(perm_prev_used);

       }

     }

     for (int j = max_level_collected; j >= 0; j -= 1) {

       // Adjust generation sizes.

       _gens[j]->compute_new_size();

     }

     if (complete) {

       // Ask the permanent generation to adjust size for full collections

       perm()->compute_new_size();

       update_full_collections_completed();

     }

     // Track memory usage and detect low memory after GC finishes

     MemoryService::track_memory_usage();

     gc_epilogue(complete);

     if (must_restore_marks_for_biased_locking) {

       BiasedLocking::restore_marks();

     }

   }

   AdaptiveSizePolicy* sp = gen_policy()->size_policy();

   AdaptiveSizePolicyOutput(sp, total_collections());

   if (PrintHeapAtGC) {

     Universe::print_heap_after_gc();

   }

 #ifdef TRACESPINNING

   ParallelTaskTerminator::print_termination_counts();

 #endif

   if (ExitAfterGCNum > 0 && total_collections() == ExitAfterGCNum) {

     tty->print_cr("Stopping after GC #%d", ExitAfterGCNum);

     vm_exit(-1);

   }

 }

 HeapWord* GenCollectedHeap::satisfy_failed_allocation(size_t size, bool is_tlab) {

   return collector_policy()->satisfy_failed_allocation(size, is_tlab);

 }

 void GenCollectedHeap::set_par_threads(int t) {

   SharedHeap::set_par_threads(t);

   _gen_process_strong_tasks->set_par_threads(t);

 }

 class AssertIsPermClosure: public OopClosure {

 public:

   void do_oop(oop* p) {

     assert((*p) == NULL || (*p)->is_perm(), "Referent should be perm.");

   }

   void do_oop(narrowOop* p) { ShouldNotReachHere(); }

 };

 static AssertIsPermClosure assert_is_perm_closure;

 void GenCollectedHeap::

 gen_process_strong_roots(int level,

                          bool younger_gens_as_roots,

                          bool collecting_perm_gen,

                          SharedHeap::ScanningOption so,

                          OopsInGenClosure* older_gens,

                          OopsInGenClosure* not_older_gens) {

   // General strong roots.

   SharedHeap::process_strong_roots(collecting_perm_gen, so,

                                    not_older_gens, older_gens);

   if (younger_gens_as_roots) {

     if (!_gen_process_strong_tasks->is_task_claimed(GCH_PS_younger_gens)) {

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

         not_older_gens->set_generation(_gens[i]);

         _gens[i]->oop_iterate(not_older_gens);

       }

       not_older_gens->reset_generation();

     }

   }

   // When collection is parallel, all threads get to cooperate to do

   // older-gen scanning.

   for (int i = level+1; i < _n_gens; i++) {

     older_gens->set_generation(_gens[i]);

     rem_set()->younger_refs_iterate(_gens[i], older_gens);

     older_gens->reset_generation();

   }

   _gen_process_strong_tasks->all_tasks_completed();

 }

 void GenCollectedHeap::gen_process_weak_roots(OopClosure* root_closure,

                                               OopClosure* non_root_closure) {

   SharedHeap::process_weak_roots(root_closure, non_root_closure);

   // "Local" "weak" refs

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->ref_processor()->weak_oops_do(root_closure);

   }

 }

 #define GCH_SINCE_SAVE_MARKS_ITERATE_DEFN(OopClosureType, nv_suffix)    \

 void GenCollectedHeap::                                                 \

 oop_since_save_marks_iterate(int level,                                 \

                              OopClosureType* cur,                       \

                              OopClosureType* older) {                   \

   _gens[level]->oop_since_save_marks_iterate##nv_suffix(cur);           \

   for (int i = level+1; i < n_gens(); i++) {                            \

     _gens[i]->oop_since_save_marks_iterate##nv_suffix(older);           \

   }                                                                     \

   perm_gen()->oop_since_save_marks_iterate##nv_suffix(older);           \

 }

 ALL_SINCE_SAVE_MARKS_CLOSURES(GCH_SINCE_SAVE_MARKS_ITERATE_DEFN)

 #undef GCH_SINCE_SAVE_MARKS_ITERATE_DEFN

 bool GenCollectedHeap::no_allocs_since_save_marks(int level) {

   for (int i = level; i < _n_gens; i++) {

     if (!_gens[i]->no_allocs_since_save_marks()) return false;

   }

   return perm_gen()->no_allocs_since_save_marks();

 }

 bool GenCollectedHeap::supports_inline_contig_alloc() const {

   return _gens[0]->supports_inline_contig_alloc();

 }

 HeapWord** GenCollectedHeap::top_addr() const {

   return _gens[0]->top_addr();

 }

 HeapWord** GenCollectedHeap::end_addr() const {

   return _gens[0]->end_addr();

 }

 size_t GenCollectedHeap::unsafe_max_alloc() {

   return _gens[0]->unsafe_max_alloc_nogc();

 }

 // public collection interfaces

 void GenCollectedHeap::collect(GCCause::Cause cause) {

   if (should_do_concurrent_full_gc(cause)) {

 #ifndef SERIALGC

     // mostly concurrent full collection

     collect_mostly_concurrent(cause);

 #else  // SERIALGC

     ShouldNotReachHere();

 #endif // SERIALGC

   } else {

 #ifdef ASSERT

     if (cause == GCCause::_scavenge_alot) {

       // minor collection only

       collect(cause, 0);

     } else {

       // Stop-the-world full collection

       collect(cause, n_gens() - 1);

     }

 #else

     // Stop-the-world full collection

     collect(cause, n_gens() - 1);

 #endif

   }

 }

 void GenCollectedHeap::collect(GCCause::Cause cause, int max_level) {

   // The caller doesn't have the Heap_lock

   assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock");

   MutexLocker ml(Heap_lock);

   collect_locked(cause, max_level);

 }

 // This interface assumes that it's being called by the

 // vm thread. It collects the heap assuming that the

 // heap lock is already held and that we are executing in

 // the context of the vm thread.

 void GenCollectedHeap::collect_as_vm_thread(GCCause::Cause cause) {

   assert(Thread::current()->is_VM_thread(), "Precondition#1");

   assert(Heap_lock->is_locked(), "Precondition#2");

   GCCauseSetter gcs(this, cause);

   switch (cause) {

     case GCCause::_heap_inspection:

     case GCCause::_heap_dump: {

       HandleMark hm;

       do_full_collection(false,         // don't clear all soft refs

                          n_gens() - 1);

       break;

     }

     default: // XXX FIX ME

       ShouldNotReachHere(); // Unexpected use of this function

   }

 }

 void GenCollectedHeap::collect_locked(GCCause::Cause cause) {

   // The caller has the Heap_lock

   assert(Heap_lock->owned_by_self(), "this thread should own the Heap_lock");

   collect_locked(cause, n_gens() - 1);

 }

 // this is the private collection interface

 // The Heap_lock is expected to be held on entry.

 void GenCollectedHeap::collect_locked(GCCause::Cause cause, int max_level) {

   if (_preloading_shared_classes) {

     warning("\nThe permanent generation is not large enough to preload "

             "requested classes.\nUse -XX:PermSize= to increase the initial "

             "size of the permanent generation.\n");

     vm_exit(2);

   }

   // Read the GC count while holding the Heap_lock

   unsigned int gc_count_before      = total_collections();

   unsigned int full_gc_count_before = total_full_collections();

   {

     MutexUnlocker mu(Heap_lock);  // give up heap lock, execute gets it back

     VM_GenCollectFull op(gc_count_before, full_gc_count_before,

                          cause, max_level);

     VMThread::execute(&op);

   }

 }

 #ifndef SERIALGC

 bool GenCollectedHeap::create_cms_collector() {

   assert(((_gens[1]->kind() == Generation::ConcurrentMarkSweep) ||

          (_gens[1]->kind() == Generation::ASConcurrentMarkSweep)) &&

          _perm_gen->as_gen()->kind() == Generation::ConcurrentMarkSweep,

          "Unexpected generation kinds");

   // Skip two header words in the block content verification

   NOT_PRODUCT(_skip_header_HeapWords = CMSCollector::skip_header_HeapWords();)

   CMSCollector* collector = new CMSCollector(

     (ConcurrentMarkSweepGeneration*)_gens[1],

     (ConcurrentMarkSweepGeneration*)_perm_gen->as_gen(),

     _rem_set->as_CardTableRS(),

     (ConcurrentMarkSweepPolicy*) collector_policy());

   if (collector == NULL || !collector->completed_initialization()) {

     if (collector) {

       delete collector;  // Be nice in embedded situation

     }

     vm_shutdown_during_initialization("Could not create CMS collector");

     return false;

   }

   return true;  // success

 }

 void GenCollectedHeap::collect_mostly_concurrent(GCCause::Cause cause) {

   assert(!Heap_lock->owned_by_self(), "Should not own Heap_lock");

   MutexLocker ml(Heap_lock);

   // Read the GC counts while holding the Heap_lock

   unsigned int full_gc_count_before = total_full_collections();

   unsigned int gc_count_before      = total_collections();

   {

     MutexUnlocker mu(Heap_lock);

     VM_GenCollectFullConcurrent op(gc_count_before, full_gc_count_before, cause);

     VMThread::execute(&op);

   }

 }

 #endif // SERIALGC

 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs,

                                           int max_level) {

   int local_max_level;

   if (!incremental_collection_will_fail() &&

       gc_cause() == GCCause::_gc_locker) {

     local_max_level = 0;

   } else {

     local_max_level = max_level;

   }

   do_collection(true                 /* full */,

                 clear_all_soft_refs  /* clear_all_soft_refs */,

                 0                    /* size */,

                 false                /* is_tlab */,

                 local_max_level      /* max_level */);

   // Hack XXX FIX ME !!!

   // A scavenge may not have been attempted, or may have

   // been attempted and failed, because the old gen was too full

   if (local_max_level == 0 && gc_cause() == GCCause::_gc_locker &&

       incremental_collection_will_fail()) {

     if (PrintGCDetails) {

       gclog_or_tty->print_cr("GC locker: Trying a full collection "

                              "because scavenge failed");

     }

     // This time allow the old gen to be collected as well

     do_collection(true                 /* full */,

                   clear_all_soft_refs  /* clear_all_soft_refs */,

                   0                    /* size */,

                   false                /* is_tlab */,

                   n_gens() - 1         /* max_level */);

   }

 }

 // Returns "TRUE" iff "p" points into the allocated area of the heap.

 bool GenCollectedHeap::is_in(const void* p) const {

   #ifndef ASSERT

   guarantee(VerifyBeforeGC   ||

             VerifyDuringGC   ||

             VerifyBeforeExit ||

             VerifyAfterGC, "too expensive");

   #endif

   // This might be sped up with a cache of the last generation that

   // answered yes.

   for (int i = 0; i < _n_gens; i++) {

     if (_gens[i]->is_in(p)) return true;

   }

   if (_perm_gen->as_gen()->is_in(p)) return true;

   // Otherwise...

   return false;

 }

 // Returns "TRUE" iff "p" points into the allocated area of the heap.

 bool GenCollectedHeap::is_in_youngest(void* p) {

   return _gens[0]->is_in(p);

 }

 void GenCollectedHeap::oop_iterate(OopClosure* cl) {

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->oop_iterate(cl);

   }

 }

 void GenCollectedHeap::oop_iterate(MemRegion mr, OopClosure* cl) {

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->oop_iterate(mr, cl);

   }

 }

 void GenCollectedHeap::object_iterate(ObjectClosure* cl) {

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->object_iterate(cl);

   }

   perm_gen()->object_iterate(cl);

 }

 void GenCollectedHeap::safe_object_iterate(ObjectClosure* cl) {

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->safe_object_iterate(cl);

   }

   perm_gen()->safe_object_iterate(cl);

 }

 void GenCollectedHeap::object_iterate_since_last_GC(ObjectClosure* cl) {

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->object_iterate_since_last_GC(cl);

   }

 }

 Space* GenCollectedHeap::space_containing(const void* addr) const {

   for (int i = 0; i < _n_gens; i++) {

     Space* res = _gens[i]->space_containing(addr);

     if (res != NULL) return res;

   }

   Space* res = perm_gen()->space_containing(addr);

   if (res != NULL) return res;

   // Otherwise...

   assert(false, "Could not find containing space");

   return NULL;

 }

 HeapWord* GenCollectedHeap::block_start(const void* addr) const {

   assert(is_in_reserved(addr), "block_start of address outside of heap");

   for (int i = 0; i < _n_gens; i++) {

     if (_gens[i]->is_in_reserved(addr)) {

       assert(_gens[i]->is_in(addr),

              "addr should be in allocated part of generation");

       return _gens[i]->block_start(addr);

     }

   }

   if (perm_gen()->is_in_reserved(addr)) {

     assert(perm_gen()->is_in(addr),

            "addr should be in allocated part of perm gen");

     return perm_gen()->block_start(addr);

   }

   assert(false, "Some generation should contain the address");

   return NULL;

 }

 size_t GenCollectedHeap::block_size(const HeapWord* addr) const {

   assert(is_in_reserved(addr), "block_size of address outside of heap");

   for (int i = 0; i < _n_gens; i++) {

     if (_gens[i]->is_in_reserved(addr)) {

       assert(_gens[i]->is_in(addr),

              "addr should be in allocated part of generation");

       return _gens[i]->block_size(addr);

     }

   }

   if (perm_gen()->is_in_reserved(addr)) {

     assert(perm_gen()->is_in(addr),

            "addr should be in allocated part of perm gen");

     return perm_gen()->block_size(addr);

   }

   assert(false, "Some generation should contain the address");

   return 0;

 }

 bool GenCollectedHeap::block_is_obj(const HeapWord* addr) const {

   assert(is_in_reserved(addr), "block_is_obj of address outside of heap");

   assert(block_start(addr) == addr, "addr must be a block start");

   for (int i = 0; i < _n_gens; i++) {

     if (_gens[i]->is_in_reserved(addr)) {

       return _gens[i]->block_is_obj(addr);

     }

   }

   if (perm_gen()->is_in_reserved(addr)) {

     return perm_gen()->block_is_obj(addr);

   }

   assert(false, "Some generation should contain the address");

   return false;

 }

 bool GenCollectedHeap::supports_tlab_allocation() const {

   for (int i = 0; i < _n_gens; i += 1) {

     if (_gens[i]->supports_tlab_allocation()) {

       return true;

     }

   }

   return false;

 }

 size_t GenCollectedHeap::tlab_capacity(Thread* thr) const {

   size_t result = 0;

   for (int i = 0; i < _n_gens; i += 1) {

     if (_gens[i]->supports_tlab_allocation()) {

       result += _gens[i]->tlab_capacity();

     }

   }

   return result;

 }

 size_t GenCollectedHeap::unsafe_max_tlab_alloc(Thread* thr) const {

   size_t result = 0;

   for (int i = 0; i < _n_gens; i += 1) {

     if (_gens[i]->supports_tlab_allocation()) {

       result += _gens[i]->unsafe_max_tlab_alloc();

     }

   }

   return result;

 }

 HeapWord* GenCollectedHeap::allocate_new_tlab(size_t size) {

   bool gc_overhead_limit_was_exceeded;

   HeapWord* result = mem_allocate(size   /* size */,

                                   false  /* is_large_noref */,

                                   true   /* is_tlab */,

                                   &gc_overhead_limit_was_exceeded);

   return result;

 }

 // Requires "*prev_ptr" to be non-NULL.  Deletes and a block of minimal size

 // from the list headed by "*prev_ptr".

 static ScratchBlock *removeSmallestScratch(ScratchBlock **prev_ptr) {

   bool first = true;

   size_t min_size = 0;   // "first" makes this conceptually infinite.

   ScratchBlock **smallest_ptr, *smallest;

   ScratchBlock  *cur = *prev_ptr;

   while (cur) {

     assert(*prev_ptr == cur, "just checking");

     if (first || cur->num_words < min_size) {

       smallest_ptr = prev_ptr;

       smallest     = cur;

       min_size     = smallest->num_words;

       first        = false;

     }

     prev_ptr = &cur->next;

     cur     =  cur->next;

   }

   smallest      = *smallest_ptr;

   *smallest_ptr = smallest->next;

   return smallest;

 }

 // Sort the scratch block list headed by res into decreasing size order,

 // and set "res" to the result.

 static void sort_scratch_list(ScratchBlock*& list) {

   ScratchBlock* sorted = NULL;

   ScratchBlock* unsorted = list;

   while (unsorted) {

     ScratchBlock *smallest = removeSmallestScratch(&unsorted);

     smallest->next  = sorted;

     sorted          = smallest;

   }

   list = sorted;

 }

 ScratchBlock* GenCollectedHeap::gather_scratch(Generation* requestor,

                                                size_t max_alloc_words) {

   ScratchBlock* res = NULL;

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->contribute_scratch(res, requestor, max_alloc_words);

   }

   sort_scratch_list(res);

   return res;

 }

 void GenCollectedHeap::release_scratch() {

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->reset_scratch();

   }

 }

 size_t GenCollectedHeap::large_typearray_limit() {

   return gen_policy()->large_typearray_limit();

 }

 class GenPrepareForVerifyClosure: public GenCollectedHeap::GenClosure {

   void do_generation(Generation* gen) {

     gen->prepare_for_verify();

   }

 };

 void GenCollectedHeap::prepare_for_verify() {

   ensure_parsability(false);        // no need to retire TLABs

   GenPrepareForVerifyClosure blk;

   generation_iterate(&blk, false);

   perm_gen()->prepare_for_verify();

 }

 void GenCollectedHeap::generation_iterate(GenClosure* cl,

                                           bool old_to_young) {

   if (old_to_young) {

     for (int i = _n_gens-1; i >= 0; i--) {

       cl->do_generation(_gens[i]);

     }

   } else {

     for (int i = 0; i < _n_gens; i++) {

       cl->do_generation(_gens[i]);

     }

   }

 }

 void GenCollectedHeap::space_iterate(SpaceClosure* cl) {

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->space_iterate(cl, true);

   }

   perm_gen()->space_iterate(cl, true);

 }

 bool GenCollectedHeap::is_maximal_no_gc() const {

   for (int i = 0; i < _n_gens; i++) {  // skip perm gen

     if (!_gens[i]->is_maximal_no_gc()) {

       return false;

     }

   }

   return true;

 }

 void GenCollectedHeap::save_marks() {

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->save_marks();

   }

   perm_gen()->save_marks();

 }

 void GenCollectedHeap::compute_new_generation_sizes(int collectedGen) {

   for (int i = 0; i <= collectedGen; i++) {

     _gens[i]->compute_new_size();

   }

 }

 GenCollectedHeap* GenCollectedHeap::heap() {

   assert(_gch != NULL, "Uninitialized access to GenCollectedHeap::heap()");

   assert(_gch->kind() == CollectedHeap::GenCollectedHeap, "not a generational heap");

   return _gch;

 }

 void GenCollectedHeap::prepare_for_compaction() {

   Generation* scanning_gen = _gens[_n_gens-1];

   // Start by compacting into same gen.

   CompactPoint cp(scanning_gen, NULL, NULL);

   while (scanning_gen != NULL) {

     scanning_gen->prepare_for_compaction(&cp);

     scanning_gen = prev_gen(scanning_gen);

   }

 }

 GCStats* GenCollectedHeap::gc_stats(int level) const {

   return _gens[level]->gc_stats();

 }

 void GenCollectedHeap::verify(bool allow_dirty, bool silent) {

   if (!silent) {

     gclog_or_tty->print("permgen ");

   }

   perm_gen()->verify(allow_dirty);

   for (int i = _n_gens-1; i >= 0; i--) {

     Generation* g = _gens[i];

     if (!silent) {

       gclog_or_tty->print(g->name());

       gclog_or_tty->print(" ");

     }

     g->verify(allow_dirty);

   }

   if (!silent) {

     gclog_or_tty->print("remset ");

   }

   rem_set()->verify();

   if (!silent) {

      gclog_or_tty->print("ref_proc ");

   }

   ReferenceProcessor::verify();

 }

 void GenCollectedHeap::print() const { print_on(tty); }

 void GenCollectedHeap::print_on(outputStream* st) const {

   for (int i = 0; i < _n_gens; i++) {

     _gens[i]->print_on(st);

   }

   perm_gen()->print_on(st);

 }

 void GenCollectedHeap::gc_threads_do(ThreadClosure* tc) const {

   if (workers() != NULL) {

     workers()->threads_do(tc);

   }

 #ifndef SERIALGC

   if (UseConcMarkSweepGC) {

     ConcurrentMarkSweepThread::threads_do(tc);

   }

 #endif // SERIALGC

 }

 void GenCollectedHeap::print_gc_threads_on(outputStream* st) const {

 #ifndef SERIALGC

   if (UseParNewGC) {

     workers()->print_worker_threads_on(st);

   }

   if (UseConcMarkSweepGC) {

     ConcurrentMarkSweepThread::print_all_on(st);

   }

 #endif // SERIALGC

 }

 void GenCollectedHeap::print_tracing_info() const {

   if (TraceGen0Time) {

     get_gen(0)->print_summary_info();

   }

   if (TraceGen1Time) {

     get_gen(1)->print_summary_info();

   }

 }

 void GenCollectedHeap::print_heap_change(size_t prev_used) const {

   if (PrintGCDetails && Verbose) {

     gclog_or_tty->print(" "  SIZE_FORMAT

                         "->" SIZE_FORMAT

                         "("  SIZE_FORMAT ")",

                         prev_used, used(), capacity());

   } else {

     gclog_or_tty->print(" "  SIZE_FORMAT "K"

                         "->" SIZE_FORMAT "K"

                         "("  SIZE_FORMAT "K)",

                         prev_used / K, used() / K, capacity() / K);

   }

 }

 //New method to print perm gen info with PrintGCDetails flag

 void GenCollectedHeap::print_perm_heap_change(size_t perm_prev_used) const {

   gclog_or_tty->print(", [%s :", perm_gen()->short_name());

   perm_gen()->print_heap_change(perm_prev_used);

   gclog_or_tty->print("]");

 }

 class GenGCPrologueClosure: public GenCollectedHeap::GenClosure {

  private:

   bool _full;

  public:

   void do_generation(Generation* gen) {

     gen->gc_prologue(_full);

   }

   GenGCPrologueClosure(bool full) : _full(full) {};

 };

 void GenCollectedHeap::gc_prologue(bool full) {

   assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");

   always_do_update_barrier = false;

   // Fill TLAB's and such

   CollectedHeap::accumulate_statistics_all_tlabs();

   ensure_parsability(true);   // retire TLABs

   // Call allocation profiler

   AllocationProfiler::iterate_since_last_gc();

   // Walk generations

   GenGCPrologueClosure blk(full);

   generation_iterate(&blk, false);  // not old-to-young.

   perm_gen()->gc_prologue(full);

 };

 class GenGCEpilogueClosure: public GenCollectedHeap::GenClosure {

  private:

   bool _full;

  public:

   void do_generation(Generation* gen) {

     gen->gc_epilogue(_full);

   }

   GenGCEpilogueClosure(bool full) : _full(full) {};

 };

 void GenCollectedHeap::gc_epilogue(bool full) {

   // Remember if a partial collection of the heap failed, and

   // we did a complete collection.

   if (full && incremental_collection_will_fail()) {

     set_last_incremental_collection_failed();

   } else {

     clear_last_incremental_collection_failed();

   }

   // Clear the flag, if set; the generation gc_epilogues will set the

   // flag again if the condition persists despite the collection.

   clear_incremental_collection_will_fail();

 #ifdef COMPILER2

   assert(DerivedPointerTable::is_empty(), "derived pointer present");

   size_t actual_gap = pointer_delta((HeapWord*) (max_uintx-3), *(end_addr()));

   guarantee(actual_gap > (size_t)FastAllocateSizeLimit, "inline allocation wraps");

 #endif /* COMPILER2 */

   resize_all_tlabs();

   GenGCEpilogueClosure blk(full);

   generation_iterate(&blk, false);  // not old-to-young.

   perm_gen()->gc_epilogue(full);

   always_do_update_barrier = UseConcMarkSweepGC;

 };

 #ifndef PRODUCT

 class GenGCSaveTopsBeforeGCClosure: public GenCollectedHeap::GenClosure {

  private:

  public:

   void do_generation(Generation* gen) {

     gen->record_spaces_top();

   }

 };

 void GenCollectedHeap::record_gen_tops_before_GC() {

   if (ZapUnusedHeapArea) {

     GenGCSaveTopsBeforeGCClosure blk;

     generation_iterate(&blk, false);  // not old-to-young.

     perm_gen()->record_spaces_top();

   }

 }

 #endif  // not PRODUCT

 class GenEnsureParsabilityClosure: public GenCollectedHeap::GenClosure {

  public:

   void do_generation(Generation* gen) {

     gen->ensure_parsability();

   }

 };

 void GenCollectedHeap::ensure_parsability(bool retire_tlabs) {

   CollectedHeap::ensure_parsability(retire_tlabs);

   GenEnsureParsabilityClosure ep_cl;

   generation_iterate(&ep_cl, false);

   perm_gen()->ensure_parsability();

 }

 oop GenCollectedHeap::handle_failed_promotion(Generation* gen,

                                               oop obj,

                                               size_t obj_size) {

   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");

   HeapWord* result = NULL;

   // First give each higher generation a chance to allocate the promoted object.

   Generation* allocator = next_gen(gen);

   if (allocator != NULL) {

     do {

       result = allocator->allocate(obj_size, false);

     } while (result == NULL && (allocator = next_gen(allocator)) != NULL);

   }

   if (result == NULL) {

     // Then give gen and higher generations a chance to expand and allocate the

     // object.

     do {

       result = gen->expand_and_allocate(obj_size, false);

     } while (result == NULL && (gen = next_gen(gen)) != NULL);

   }

   if (result != NULL) {

     Copy::aligned_disjoint_words((HeapWord*)obj, result, obj_size);

   }

   return oop(result);

 }

 class GenTimeOfLastGCClosure: public GenCollectedHeap::GenClosure {

   jlong _time;   // in ms

   jlong _now;    // in ms

  public:

   GenTimeOfLastGCClosure(jlong now) : _time(now), _now(now) { }

   jlong time() { return _time; }

   void do_generation(Generation* gen) {

     _time = MIN2(_time, gen->time_of_last_gc(_now));

   }

 };

 jlong GenCollectedHeap::millis_since_last_gc() {

   jlong now = os::javaTimeMillis();

   GenTimeOfLastGCClosure tolgc_cl(now);

   // iterate over generations getting the oldest

   // time that a generation was collected

   generation_iterate(&tolgc_cl, false);

   tolgc_cl.do_generation(perm_gen());

   // XXX Despite the assert above, since javaTimeMillis()

   // doesnot guarantee monotonically increasing return

   // values (note, i didn't say "strictly monotonic"),

   // we need to guard against getting back a time

   // later than now. This should be fixed by basing

   // on someting like gethrtime() which guarantees

   // monotonicity. Note that cond_wait() is susceptible

   // to a similar problem, because its interface is

   // based on absolute time in the form of the

   // system time's notion of UCT. See also 4506635

   // for yet another problem of similar nature. XXX

   jlong retVal = now - tolgc_cl.time();

   if (retVal < 0) {

     NOT_PRODUCT(warning("time warp: %d", retVal);)

     return 0;

   }

   return retVal;

 }