1 /*

     2  * Copyright 2001-2007 Sun Microsystems, Inc.  All Rights Reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

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

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

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

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

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

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

    13  * accompanied this code).

    14  *

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

    16  * 2 along with this work; if not, write to the Free Software Foundation,

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

    18  *

    19  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    20  * CA 95054 USA or visit www.sun.com if you need additional information or

    21  * have any questions.

    22  *

    23  */

    24 

    25 // A "G1CollectedHeap" is an implementation of a java heap for HotSpot.

    26 // It uses the "Garbage First" heap organization and algorithm, which

    27 // may combine concurrent marking with parallel, incremental compaction of

    28 // heap subsets that will yield large amounts of garbage.

    29 

    30 class HeapRegion;

    31 class HeapRegionSeq;

    32 class HeapRegionList;

    33 class PermanentGenerationSpec;

    34 class GenerationSpec;

    35 class OopsInHeapRegionClosure;

    36 class G1ScanHeapEvacClosure;

    37 class ObjectClosure;

    38 class SpaceClosure;

    39 class CompactibleSpaceClosure;

    40 class Space;

    41 class G1CollectorPolicy;

    42 class GenRemSet;

    43 class G1RemSet;

    44 class HeapRegionRemSetIterator;

    45 class ConcurrentMark;

    46 class ConcurrentMarkThread;

    47 class ConcurrentG1Refine;

    48 class ConcurrentZFThread;

    49 

    50 // If want to accumulate detailed statistics on work queues

    51 // turn this on.

    52 #define G1_DETAILED_STATS 0

    53 

    54 #if G1_DETAILED_STATS

    55 #  define IF_G1_DETAILED_STATS(code) code

    56 #else

    57 #  define IF_G1_DETAILED_STATS(code)

    58 #endif

    59 

    60 typedef GenericTaskQueue<oop*>    RefToScanQueue;

    61 typedef GenericTaskQueueSet<oop*> RefToScanQueueSet;

    62 

    63 enum G1GCThreadGroups {

    64   G1CRGroup = 0,

    65   G1ZFGroup = 1,

    66   G1CMGroup = 2,

    67   G1CLGroup = 3

    68 };

    69 

    70 enum GCAllocPurpose {

    71   GCAllocForTenured,

    72   GCAllocForSurvived,

    73   GCAllocPurposeCount

    74 };

    75 

    76 class YoungList : public CHeapObj {

    77 private:

    78   G1CollectedHeap* _g1h;

    79 

    80   HeapRegion* _head;

    81 

    82   HeapRegion* _scan_only_head;

    83   HeapRegion* _scan_only_tail;

    84   size_t      _length;

    85   size_t      _scan_only_length;

    86 

    87   size_t      _last_sampled_rs_lengths;

    88   size_t      _sampled_rs_lengths;

    89   HeapRegion* _curr;

    90   HeapRegion* _curr_scan_only;

    91 

    92   HeapRegion* _survivor_head;

    93   HeapRegion* _survivors_tail;

    94   size_t      _survivor_length;

    95 

    96   void          empty_list(HeapRegion* list);

    97 

    98 public:

    99   YoungList(G1CollectedHeap* g1h);

   100 

   101   void          push_region(HeapRegion* hr);

   102   void          add_survivor_region(HeapRegion* hr);

   103   HeapRegion*   pop_region();

   104   void          empty_list();

   105   bool          is_empty() { return _length == 0; }

   106   size_t        length() { return _length; }

   107   size_t        scan_only_length() { return _scan_only_length; }

   108 

   109   void rs_length_sampling_init();

   110   bool rs_length_sampling_more();

   111   void rs_length_sampling_next();

   112 

   113   void reset_sampled_info() {

   114     _last_sampled_rs_lengths =   0;

   115   }

   116   size_t sampled_rs_lengths() { return _last_sampled_rs_lengths; }

   117 

   118   // for development purposes

   119   void reset_auxilary_lists();

   120   HeapRegion* first_region() { return _head; }

   121   HeapRegion* first_scan_only_region() { return _scan_only_head; }

   122   HeapRegion* first_survivor_region() { return _survivor_head; }

   123   HeapRegion* par_get_next_scan_only_region() {

   124     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);

   125     HeapRegion* ret = _curr_scan_only;

   126     if (ret != NULL)

   127       _curr_scan_only = ret->get_next_young_region();

   128     return ret;

   129   }

   130 

   131   // debugging

   132   bool          check_list_well_formed();

   133   bool          check_list_empty(bool ignore_scan_only_list,

   134                                  bool check_sample = true);

   135   void          print();

   136 };

   137 

   138 class RefineCardTableEntryClosure;

   139 class G1CollectedHeap : public SharedHeap {

   140   friend class VM_G1CollectForAllocation;

   141   friend class VM_GenCollectForPermanentAllocation;

   142   friend class VM_G1CollectFull;

   143   friend class VM_G1IncCollectionPause;

   144   friend class VM_G1PopRegionCollectionPause;

   145   friend class VMStructs;

   146 

   147   // Closures used in implementation.

   148   friend class G1ParCopyHelper;

   149   friend class G1IsAliveClosure;

   150   friend class G1EvacuateFollowersClosure;

   151   friend class G1ParScanThreadState;

   152   friend class G1ParScanClosureSuper;

   153   friend class G1ParEvacuateFollowersClosure;

   154   friend class G1ParTask;

   155   friend class G1FreeGarbageRegionClosure;

   156   friend class RefineCardTableEntryClosure;

   157   friend class G1PrepareCompactClosure;

   158   friend class RegionSorter;

   159   friend class CountRCClosure;

   160   friend class EvacPopObjClosure;

   161 

   162   // Other related classes.

   163   friend class G1MarkSweep;

   164 

   165 private:

   166   enum SomePrivateConstants {

   167     VeryLargeInBytes = HeapRegion::GrainBytes/2,

   168     VeryLargeInWords = VeryLargeInBytes/HeapWordSize,

   169     MinHeapDeltaBytes = 10 * HeapRegion::GrainBytes,      // FIXME

   170     NumAPIs = HeapRegion::MaxAge

   171   };

   172 

   173 

   174   // The one and only G1CollectedHeap, so static functions can find it.

   175   static G1CollectedHeap* _g1h;

   176 

   177   // Storage for the G1 heap (excludes the permanent generation).

   178   VirtualSpace _g1_storage;

   179   MemRegion    _g1_reserved;

   180 

   181   // The part of _g1_storage that is currently committed.

   182   MemRegion _g1_committed;

   183 

   184   // The maximum part of _g1_storage that has ever been committed.

   185   MemRegion _g1_max_committed;

   186 

   187   // The number of regions that are completely free.

   188   size_t _free_regions;

   189 

   190   // The number of regions we could create by expansion.

   191   size_t _expansion_regions;

   192 

   193   // Return the number of free regions in the heap (by direct counting.)

   194   size_t count_free_regions();

   195   // Return the number of free regions on the free and unclean lists.

   196   size_t count_free_regions_list();

   197 

   198   // The block offset table for the G1 heap.

   199   G1BlockOffsetSharedArray* _bot_shared;

   200 

   201   // Move all of the regions off the free lists, then rebuild those free

   202   // lists, before and after full GC.

   203   void tear_down_region_lists();

   204   void rebuild_region_lists();

   205   // This sets all non-empty regions to need zero-fill (which they will if

   206   // they are empty after full collection.)

   207   void set_used_regions_to_need_zero_fill();

   208 

   209   // The sequence of all heap regions in the heap.

   210   HeapRegionSeq* _hrs;

   211 

   212   // The region from which normal-sized objects are currently being

   213   // allocated.  May be NULL.

   214   HeapRegion* _cur_alloc_region;

   215 

   216   // Postcondition: cur_alloc_region == NULL.

   217   void abandon_cur_alloc_region();

   218 

   219   // The to-space memory regions into which objects are being copied during

   220   // a GC.

   221   HeapRegion* _gc_alloc_regions[GCAllocPurposeCount];

   222   uint _gc_alloc_region_counts[GCAllocPurposeCount];

   223 

   224   // A list of the regions that have been set to be alloc regions in the

   225   // current collection.

   226   HeapRegion* _gc_alloc_region_list;

   227 

   228   // When called by par thread, require par_alloc_during_gc_lock() to be held.

   229   void push_gc_alloc_region(HeapRegion* hr);

   230 

   231   // This should only be called single-threaded.  Undeclares all GC alloc

   232   // regions.

   233   void forget_alloc_region_list();

   234 

   235   // Should be used to set an alloc region, because there's other

   236   // associated bookkeeping.

   237   void set_gc_alloc_region(int purpose, HeapRegion* r);

   238 

   239   // Check well-formedness of alloc region list.

   240   bool check_gc_alloc_regions();

   241 

   242   // Outside of GC pauses, the number of bytes used in all regions other

   243   // than the current allocation region.

   244   size_t _summary_bytes_used;

   245 

   246   // Summary information about popular objects; method to print it.

   247   NumberSeq _pop_obj_rc_at_copy;

   248   void print_popularity_summary_info() const;

   249 

   250   unsigned _gc_time_stamp;

   251 

   252   size_t* _surviving_young_words;

   253 

   254   void setup_surviving_young_words();

   255   void update_surviving_young_words(size_t* surv_young_words);

   256   void cleanup_surviving_young_words();

   257 

   258 protected:

   259 

   260   // Returns "true" iff none of the gc alloc regions have any allocations

   261   // since the last call to "save_marks".

   262   bool all_alloc_regions_no_allocs_since_save_marks();

   263   // Calls "note_end_of_copying on all gc alloc_regions.

   264   void all_alloc_regions_note_end_of_copying();

   265 

   266   // The number of regions allocated to hold humongous objects.

   267   int         _num_humongous_regions;

   268   YoungList*  _young_list;

   269 

   270   // The current policy object for the collector.

   271   G1CollectorPolicy* _g1_policy;

   272 

   273   // Parallel allocation lock to protect the current allocation region.

   274   Mutex  _par_alloc_during_gc_lock;

   275   Mutex* par_alloc_during_gc_lock() { return &_par_alloc_during_gc_lock; }

   276 

   277   // If possible/desirable, allocate a new HeapRegion for normal object

   278   // allocation sufficient for an allocation of the given "word_size".

   279   // If "do_expand" is true, will attempt to expand the heap if necessary

   280   // to to satisfy the request.  If "zero_filled" is true, requires a

   281   // zero-filled region.

   282   // (Returning NULL will trigger a GC.)

   283   virtual HeapRegion* newAllocRegion_work(size_t word_size,

   284                                           bool do_expand,

   285                                           bool zero_filled);

   286 

   287   virtual HeapRegion* newAllocRegion(size_t word_size,

   288                                      bool zero_filled = true) {

   289     return newAllocRegion_work(word_size, false, zero_filled);

   290   }

   291   virtual HeapRegion* newAllocRegionWithExpansion(int purpose,

   292                                                   size_t word_size,

   293                                                   bool zero_filled = true);

   294 

   295   // Attempt to allocate an object of the given (very large) "word_size".

   296   // Returns "NULL" on failure.

   297   virtual HeapWord* humongousObjAllocate(size_t word_size);

   298 

   299   // If possible, allocate a block of the given word_size, else return "NULL".

   300   // Returning NULL will trigger GC or heap expansion.

   301   // These two methods have rather awkward pre- and

   302   // post-conditions. If they are called outside a safepoint, then

   303   // they assume that the caller is holding the heap lock. Upon return

   304   // they release the heap lock, if they are returning a non-NULL

   305   // value. attempt_allocation_slow() also dirties the cards of a

   306   // newly-allocated young region after it releases the heap

   307   // lock. This change in interface was the neatest way to achieve

   308   // this card dirtying without affecting mem_allocate(), which is a

   309   // more frequently called method. We tried two or three different

   310   // approaches, but they were even more hacky.

   311   HeapWord* attempt_allocation(size_t word_size,

   312                                bool permit_collection_pause = true);

   313 

   314   HeapWord* attempt_allocation_slow(size_t word_size,

   315                                     bool permit_collection_pause = true);

   316 

   317   // Allocate blocks during garbage collection. Will ensure an

   318   // allocation region, either by picking one or expanding the

   319   // heap, and then allocate a block of the given size. The block

   320   // may not be a humongous - it must fit into a single heap region.

   321   HeapWord* allocate_during_gc(GCAllocPurpose purpose, size_t word_size);

   322   HeapWord* par_allocate_during_gc(GCAllocPurpose purpose, size_t word_size);

   323 

   324   HeapWord* allocate_during_gc_slow(GCAllocPurpose purpose,

   325                                     HeapRegion*    alloc_region,

   326                                     bool           par,

   327                                     size_t         word_size);

   328 

   329   // Ensure that no further allocations can happen in "r", bearing in mind

   330   // that parallel threads might be attempting allocations.

   331   void par_allocate_remaining_space(HeapRegion* r);

   332 

   333   // Helper function for two callbacks below.

   334   // "full", if true, indicates that the GC is for a System.gc() request,

   335   // and should collect the entire heap.  If "clear_all_soft_refs" is true,

   336   // all soft references are cleared during the GC.  If "full" is false,

   337   // "word_size" describes the allocation that the GC should

   338   // attempt (at least) to satisfy.

   339   void do_collection(bool full, bool clear_all_soft_refs,

   340                      size_t word_size);

   341 

   342   // Callback from VM_G1CollectFull operation.

   343   // Perform a full collection.

   344   void do_full_collection(bool clear_all_soft_refs);

   345 

   346   // Resize the heap if necessary after a full collection.  If this is

   347   // after a collect-for allocation, "word_size" is the allocation size,

   348   // and will be considered part of the used portion of the heap.

   349   void resize_if_necessary_after_full_collection(size_t word_size);

   350 

   351   // Callback from VM_G1CollectForAllocation operation.

   352   // This function does everything necessary/possible to satisfy a

   353   // failed allocation request (including collection, expansion, etc.)

   354   HeapWord* satisfy_failed_allocation(size_t word_size);

   355 

   356   // Attempting to expand the heap sufficiently

   357   // to support an allocation of the given "word_size".  If

   358   // successful, perform the allocation and return the address of the

   359   // allocated block, or else "NULL".

   360   virtual HeapWord* expand_and_allocate(size_t word_size);

   361 

   362 public:

   363   // Expand the garbage-first heap by at least the given size (in bytes!).

   364   // (Rounds up to a HeapRegion boundary.)

   365   virtual void expand(size_t expand_bytes);

   366 

   367   // Do anything common to GC's.

   368   virtual void gc_prologue(bool full);

   369   virtual void gc_epilogue(bool full);

   370 

   371 protected:

   372 

   373   // Shrink the garbage-first heap by at most the given size (in bytes!).

   374   // (Rounds down to a HeapRegion boundary.)

   375   virtual void shrink(size_t expand_bytes);

   376   void shrink_helper(size_t expand_bytes);

   377 

   378   // Do an incremental collection: identify a collection set, and evacuate

   379   // its live objects elsewhere.

   380   virtual void do_collection_pause();

   381 

   382   // The guts of the incremental collection pause, executed by the vm

   383   // thread.  If "popular_region" is non-NULL, this pause should evacuate

   384   // this single region whose remembered set has gotten large, moving

   385   // any popular objects to one of the popular regions.

   386   virtual void do_collection_pause_at_safepoint(HeapRegion* popular_region);

   387 

   388   // Actually do the work of evacuating the collection set.

   389   virtual void evacuate_collection_set();

   390 

   391   // If this is an appropriate right time, do a collection pause.

   392   // The "word_size" argument, if non-zero, indicates the size of an

   393   // allocation request that is prompting this query.

   394   void do_collection_pause_if_appropriate(size_t word_size);

   395 

   396   // The g1 remembered set of the heap.

   397   G1RemSet* _g1_rem_set;

   398   // And it's mod ref barrier set, used to track updates for the above.

   399   ModRefBarrierSet* _mr_bs;

   400 

   401   // The Heap Region Rem Set Iterator.

   402   HeapRegionRemSetIterator** _rem_set_iterator;

   403 

   404   // The closure used to refine a single card.

   405   RefineCardTableEntryClosure* _refine_cte_cl;

   406 

   407   // A function to check the consistency of dirty card logs.

   408   void check_ct_logs_at_safepoint();

   409 

   410   // After a collection pause, make the regions in the CS into free

   411   // regions.

   412   void free_collection_set(HeapRegion* cs_head);

   413 

   414   // Applies "scan_non_heap_roots" to roots outside the heap,

   415   // "scan_rs" to roots inside the heap (having done "set_region" to

   416   // indicate the region in which the root resides), and does "scan_perm"

   417   // (setting the generation to the perm generation.)  If "scan_rs" is

   418   // NULL, then this step is skipped.  The "worker_i"

   419   // param is for use with parallel roots processing, and should be

   420   // the "i" of the calling parallel worker thread's work(i) function.

   421   // In the sequential case this param will be ignored.

   422   void g1_process_strong_roots(bool collecting_perm_gen,

   423                                SharedHeap::ScanningOption so,

   424                                OopClosure* scan_non_heap_roots,

   425                                OopsInHeapRegionClosure* scan_rs,

   426                                OopsInHeapRegionClosure* scan_so,

   427                                OopsInGenClosure* scan_perm,

   428                                int worker_i);

   429 

   430   void scan_scan_only_set(OopsInHeapRegionClosure* oc,

   431                           int worker_i);

   432   void scan_scan_only_region(HeapRegion* hr,

   433                              OopsInHeapRegionClosure* oc,

   434                              int worker_i);

   435 

   436   // Apply "blk" to all the weak roots of the system.  These include

   437   // JNI weak roots, the code cache, system dictionary, symbol table,

   438   // string table, and referents of reachable weak refs.

   439   void g1_process_weak_roots(OopClosure* root_closure,

   440                              OopClosure* non_root_closure);

   441 

   442   // Invoke "save_marks" on all heap regions.

   443   void save_marks();

   444 

   445   // Free a heap region.

   446   void free_region(HeapRegion* hr);

   447   // A component of "free_region", exposed for 'batching'.

   448   // All the params after "hr" are out params: the used bytes of the freed

   449   // region(s), the number of H regions cleared, the number of regions

   450   // freed, and pointers to the head and tail of a list of freed contig

   451   // regions, linked throught the "next_on_unclean_list" field.

   452   void free_region_work(HeapRegion* hr,

   453                         size_t& pre_used,

   454                         size_t& cleared_h,

   455                         size_t& freed_regions,

   456                         UncleanRegionList* list,

   457                         bool par = false);

   458 

   459 

   460   // The concurrent marker (and the thread it runs in.)

   461   ConcurrentMark* _cm;

   462   ConcurrentMarkThread* _cmThread;

   463   bool _mark_in_progress;

   464 

   465   // The concurrent refiner.

   466   ConcurrentG1Refine* _cg1r;

   467 

   468   // The concurrent zero-fill thread.

   469   ConcurrentZFThread* _czft;

   470 

   471   // The parallel task queues

   472   RefToScanQueueSet *_task_queues;

   473 

   474   // True iff a evacuation has failed in the current collection.

   475   bool _evacuation_failed;

   476 

   477   // Set the attribute indicating whether evacuation has failed in the

   478   // current collection.

   479   void set_evacuation_failed(bool b) { _evacuation_failed = b; }

   480 

   481   // Failed evacuations cause some logical from-space objects to have

   482   // forwarding pointers to themselves.  Reset them.

   483   void remove_self_forwarding_pointers();

   484 

   485   // When one is non-null, so is the other.  Together, they each pair is

   486   // an object with a preserved mark, and its mark value.

   487   GrowableArray<oop>*     _objs_with_preserved_marks;

   488   GrowableArray<markOop>* _preserved_marks_of_objs;

   489 

   490   // Preserve the mark of "obj", if necessary, in preparation for its mark

   491   // word being overwritten with a self-forwarding-pointer.

   492   void preserve_mark_if_necessary(oop obj, markOop m);

   493 

   494   // The stack of evac-failure objects left to be scanned.

   495   GrowableArray<oop>*    _evac_failure_scan_stack;

   496   // The closure to apply to evac-failure objects.

   497 

   498   OopsInHeapRegionClosure* _evac_failure_closure;

   499   // Set the field above.

   500   void

   501   set_evac_failure_closure(OopsInHeapRegionClosure* evac_failure_closure) {

   502     _evac_failure_closure = evac_failure_closure;

   503   }

   504 

   505   // Push "obj" on the scan stack.

   506   void push_on_evac_failure_scan_stack(oop obj);

   507   // Process scan stack entries until the stack is empty.

   508   void drain_evac_failure_scan_stack();

   509   // True iff an invocation of "drain_scan_stack" is in progress; to

   510   // prevent unnecessary recursion.

   511   bool _drain_in_progress;

   512 

   513   // Do any necessary initialization for evacuation-failure handling.

   514   // "cl" is the closure that will be used to process evac-failure

   515   // objects.

   516   void init_for_evac_failure(OopsInHeapRegionClosure* cl);

   517   // Do any necessary cleanup for evacuation-failure handling data

   518   // structures.

   519   void finalize_for_evac_failure();

   520 

   521   // An attempt to evacuate "obj" has failed; take necessary steps.

   522   void handle_evacuation_failure(oop obj);

   523   oop handle_evacuation_failure_par(OopsInHeapRegionClosure* cl, oop obj);

   524   void handle_evacuation_failure_common(oop obj, markOop m);

   525 

   526 

   527   // Ensure that the relevant gc_alloc regions are set.

   528   void get_gc_alloc_regions();

   529   // We're done with GC alloc regions; release them, as appropriate.

   530   void release_gc_alloc_regions();

   531 

   532   // ("Weak") Reference processing support

   533   ReferenceProcessor* _ref_processor;

   534 

   535   enum G1H_process_strong_roots_tasks {

   536     G1H_PS_mark_stack_oops_do,

   537     G1H_PS_refProcessor_oops_do,

   538     // Leave this one last.

   539     G1H_PS_NumElements

   540   };

   541 

   542   SubTasksDone* _process_strong_tasks;

   543 

   544   // Allocate space to hold a popular object.  Result is guaranteed below

   545   // "popular_object_boundary()".  Note: CURRENTLY halts the system if we

   546   // run out of space to hold popular objects.

   547   HeapWord* allocate_popular_object(size_t word_size);

   548 

   549   // The boundary between popular and non-popular objects.

   550   HeapWord* _popular_object_boundary;

   551 

   552   HeapRegionList* _popular_regions_to_be_evacuated;

   553 

   554   // Compute which objects in "single_region" are popular.  If any are,

   555   // evacuate them to a popular region, leaving behind forwarding pointers,

   556   // and select "popular_region" as the single collection set region.

   557   // Otherwise, leave the collection set null.

   558   void popularity_pause_preamble(HeapRegion* populer_region);

   559 

   560   // Compute which objects in "single_region" are popular, and evacuate

   561   // them to a popular region, leaving behind forwarding pointers.

   562   // Returns "true" if at least one popular object is discovered and

   563   // evacuated.  In any case, "*max_rc" is set to the maximum reference

   564   // count of an object in the region.

   565   bool compute_reference_counts_and_evac_popular(HeapRegion* populer_region,

   566                                                  size_t* max_rc);

   567   // Subroutines used in the above.

   568   bool _rc_region_above;

   569   size_t _rc_region_diff;

   570   jint* obj_rc_addr(oop obj) {

   571     uintptr_t obj_addr = (uintptr_t)obj;

   572     if (_rc_region_above) {

   573       jint* res = (jint*)(obj_addr + _rc_region_diff);

   574       assert((uintptr_t)res > obj_addr, "RC region is above.");

   575       return res;

   576     } else {

   577       jint* res = (jint*)(obj_addr - _rc_region_diff);

   578       assert((uintptr_t)res < obj_addr, "RC region is below.");

   579       return res;

   580     }

   581   }

   582   jint obj_rc(oop obj) {

   583     return *obj_rc_addr(obj);

   584   }

   585   void inc_obj_rc(oop obj) {

   586     (*obj_rc_addr(obj))++;

   587   }

   588   void atomic_inc_obj_rc(oop obj);

   589 

   590 

   591   // Number of popular objects and bytes (latter is cheaper!).

   592   size_t pop_object_used_objs();

   593   size_t pop_object_used_bytes();

   594 

   595   // Index of the popular region in which allocation is currently being

   596   // done.

   597   int _cur_pop_hr_index;

   598 

   599   // List of regions which require zero filling.

   600   UncleanRegionList _unclean_region_list;

   601   bool _unclean_regions_coming;

   602 

   603   bool check_age_cohort_well_formed_work(int a, HeapRegion* hr);

   604 

   605 public:

   606   void set_refine_cte_cl_concurrency(bool concurrent);

   607 

   608   RefToScanQueue *task_queue(int i);

   609 

   610   // Create a G1CollectedHeap with the specified policy.

   611   // Must call the initialize method afterwards.

   612   // May not return if something goes wrong.

   613   G1CollectedHeap(G1CollectorPolicy* policy);

   614 

   615   // Initialize the G1CollectedHeap to have the initial and

   616   // maximum sizes, permanent generation, and remembered and barrier sets

   617   // specified by the policy object.

   618   jint initialize();

   619 

   620   void ref_processing_init();

   621 

   622   void set_par_threads(int t) {

   623     SharedHeap::set_par_threads(t);

   624     _process_strong_tasks->set_par_threads(t);

   625   }

   626 

   627   virtual CollectedHeap::Name kind() const {

   628     return CollectedHeap::G1CollectedHeap;

   629   }

   630 

   631   // The current policy object for the collector.

   632   G1CollectorPolicy* g1_policy() const { return _g1_policy; }

   633 

   634   // Adaptive size policy.  No such thing for g1.

   635   virtual AdaptiveSizePolicy* size_policy() { return NULL; }

   636 

   637   // The rem set and barrier set.

   638   G1RemSet* g1_rem_set() const { return _g1_rem_set; }

   639   ModRefBarrierSet* mr_bs() const { return _mr_bs; }

   640 

   641   // The rem set iterator.

   642   HeapRegionRemSetIterator* rem_set_iterator(int i) {

   643     return _rem_set_iterator[i];

   644   }

   645 

   646   HeapRegionRemSetIterator* rem_set_iterator() {

   647     return _rem_set_iterator[0];

   648   }

   649 

   650   unsigned get_gc_time_stamp() {

   651     return _gc_time_stamp;

   652   }

   653 

   654   void reset_gc_time_stamp() {

   655     _gc_time_stamp = 0;

   656   }

   657 

   658   void iterate_dirty_card_closure(bool concurrent, int worker_i);

   659 

   660   // The shared block offset table array.

   661   G1BlockOffsetSharedArray* bot_shared() const { return _bot_shared; }

   662 

   663   // Reference Processing accessor

   664   ReferenceProcessor* ref_processor() { return _ref_processor; }

   665 

   666   // Reserved (g1 only; super method includes perm), capacity and the used

   667   // portion in bytes.

   668   size_t g1_reserved_obj_bytes() { return _g1_reserved.byte_size(); }

   669   virtual size_t capacity() const;

   670   virtual size_t used() const;

   671   size_t recalculate_used() const;

   672 #ifndef PRODUCT

   673   size_t recalculate_used_regions() const;

   674 #endif // PRODUCT

   675 

   676   // These virtual functions do the actual allocation.

   677   virtual HeapWord* mem_allocate(size_t word_size,

   678                                  bool   is_noref,

   679                                  bool   is_tlab,

   680                                  bool* gc_overhead_limit_was_exceeded);

   681 

   682   // Some heaps may offer a contiguous region for shared non-blocking

   683   // allocation, via inlined code (by exporting the address of the top and

   684   // end fields defining the extent of the contiguous allocation region.)

   685   // But G1CollectedHeap doesn't yet support this.

   686 

   687   // Return an estimate of the maximum allocation that could be performed

   688   // without triggering any collection or expansion activity.  In a

   689   // generational collector, for example, this is probably the largest

   690   // allocation that could be supported (without expansion) in the youngest

   691   // generation.  It is "unsafe" because no locks are taken; the result

   692   // should be treated as an approximation, not a guarantee, for use in

   693   // heuristic resizing decisions.

   694   virtual size_t unsafe_max_alloc();

   695 

   696   virtual bool is_maximal_no_gc() const {

   697     return _g1_storage.uncommitted_size() == 0;

   698   }

   699 

   700   // The total number of regions in the heap.

   701   size_t n_regions();

   702 

   703   // The number of regions that are completely free.

   704   size_t max_regions();

   705 

   706   // The number of regions that are completely free.

   707   size_t free_regions();

   708 

   709   // The number of regions that are not completely free.

   710   size_t used_regions() { return n_regions() - free_regions(); }

   711 

   712   // True iff the ZF thread should run.

   713   bool should_zf();

   714 

   715   // The number of regions available for "regular" expansion.

   716   size_t expansion_regions() { return _expansion_regions; }

   717 

   718 #ifndef PRODUCT

   719   bool regions_accounted_for();

   720   bool print_region_accounting_info();

   721   void print_region_counts();

   722 #endif

   723 

   724   HeapRegion* alloc_region_from_unclean_list(bool zero_filled);

   725   HeapRegion* alloc_region_from_unclean_list_locked(bool zero_filled);

   726 

   727   void put_region_on_unclean_list(HeapRegion* r);

   728   void put_region_on_unclean_list_locked(HeapRegion* r);

   729 

   730   void prepend_region_list_on_unclean_list(UncleanRegionList* list);

   731   void prepend_region_list_on_unclean_list_locked(UncleanRegionList* list);

   732 

   733   void set_unclean_regions_coming(bool b);

   734   void set_unclean_regions_coming_locked(bool b);

   735   // Wait for cleanup to be complete.

   736   void wait_for_cleanup_complete();

   737   // Like above, but assumes that the calling thread owns the Heap_lock.

   738   void wait_for_cleanup_complete_locked();

   739 

   740   // Return the head of the unclean list.

   741   HeapRegion* peek_unclean_region_list_locked();

   742   // Remove and return the head of the unclean list.

   743   HeapRegion* pop_unclean_region_list_locked();

   744 

   745   // List of regions which are zero filled and ready for allocation.

   746   HeapRegion* _free_region_list;

   747   // Number of elements on the free list.

   748   size_t _free_region_list_size;

   749 

   750   // If the head of the unclean list is ZeroFilled, move it to the free

   751   // list.

   752   bool move_cleaned_region_to_free_list_locked();

   753   bool move_cleaned_region_to_free_list();

   754 

   755   void put_free_region_on_list_locked(HeapRegion* r);

   756   void put_free_region_on_list(HeapRegion* r);

   757 

   758   // Remove and return the head element of the free list.

   759   HeapRegion* pop_free_region_list_locked();

   760 

   761   // If "zero_filled" is true, we first try the free list, then we try the

   762   // unclean list, zero-filling the result.  If "zero_filled" is false, we

   763   // first try the unclean list, then the zero-filled list.

   764   HeapRegion* alloc_free_region_from_lists(bool zero_filled);

   765 

   766   // Verify the integrity of the region lists.

   767   void remove_allocated_regions_from_lists();

   768   bool verify_region_lists();

   769   bool verify_region_lists_locked();

   770   size_t unclean_region_list_length();

   771   size_t free_region_list_length();

   772 

   773   // Perform a collection of the heap; intended for use in implementing

   774   // "System.gc".  This probably implies as full a collection as the

   775   // "CollectedHeap" supports.

   776   virtual void collect(GCCause::Cause cause);

   777 

   778   // The same as above but assume that the caller holds the Heap_lock.

   779   void collect_locked(GCCause::Cause cause);

   780 

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

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

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

   784   // the context of the vm thread.

   785   virtual void collect_as_vm_thread(GCCause::Cause cause);

   786 

   787   // True iff a evacuation has failed in the most-recent collection.

   788   bool evacuation_failed() { return _evacuation_failed; }

   789 

   790   // Free a region if it is totally full of garbage.  Returns the number of

   791   // bytes freed (0 ==> didn't free it).

   792   size_t free_region_if_totally_empty(HeapRegion *hr);

   793   void free_region_if_totally_empty_work(HeapRegion *hr,

   794                                          size_t& pre_used,

   795                                          size_t& cleared_h_regions,

   796                                          size_t& freed_regions,

   797                                          UncleanRegionList* list,

   798                                          bool par = false);

   799 

   800   // If we've done free region work that yields the given changes, update

   801   // the relevant global variables.

   802   void finish_free_region_work(size_t pre_used,

   803                                size_t cleared_h_regions,

   804                                size_t freed_regions,

   805                                UncleanRegionList* list);

   806 

   807 

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

   809   virtual bool is_in(const void* p) const;

   810 

   811   // Return "TRUE" iff the given object address is within the collection

   812   // set.

   813   inline bool obj_in_cs(oop obj);

   814 

   815   // Return "TRUE" iff the given object address is in the reserved

   816   // region of g1 (excluding the permanent generation).

   817   bool is_in_g1_reserved(const void* p) const {

   818     return _g1_reserved.contains(p);

   819   }

   820 

   821   // Returns a MemRegion that corresponds to the space that  has been

   822   // committed in the heap

   823   MemRegion g1_committed() {

   824     return _g1_committed;

   825   }

   826 

   827   NOT_PRODUCT( bool is_in_closed_subset(const void* p) const; )

   828 

   829   // Dirty card table entries covering a list of young regions.

   830   void dirtyCardsForYoungRegions(CardTableModRefBS* ct_bs, HeapRegion* list);

   831 

   832   // This resets the card table to all zeros.  It is used after

   833   // a collection pause which used the card table to claim cards.

   834   void cleanUpCardTable();

   835 

   836   // Iteration functions.

   837 

   838   // Iterate over all the ref-containing fields of all objects, calling

   839   // "cl.do_oop" on each.

   840   virtual void oop_iterate(OopClosure* cl);

   841 

   842   // Same as above, restricted to a memory region.

   843   virtual void oop_iterate(MemRegion mr, OopClosure* cl);

   844 

   845   // Iterate over all objects, calling "cl.do_object" on each.

   846   virtual void object_iterate(ObjectClosure* cl);

   847 

   848   // Iterate over all objects allocated since the last collection, calling

   849   // "cl.do_object" on each.  The heap must have been initialized properly

   850   // to support this function, or else this call will fail.

   851   virtual void object_iterate_since_last_GC(ObjectClosure* cl);

   852 

   853   // Iterate over all spaces in use in the heap, in ascending address order.

   854   virtual void space_iterate(SpaceClosure* cl);

   855 

   856   // Iterate over heap regions, in address order, terminating the

   857   // iteration early if the "doHeapRegion" method returns "true".

   858   void heap_region_iterate(HeapRegionClosure* blk);

   859 

   860   // Iterate over heap regions starting with r (or the first region if "r"

   861   // is NULL), in address order, terminating early if the "doHeapRegion"

   862   // method returns "true".

   863   void heap_region_iterate_from(HeapRegion* r, HeapRegionClosure* blk);

   864 

   865   // As above but starting from the region at index idx.

   866   void heap_region_iterate_from(int idx, HeapRegionClosure* blk);

   867 

   868   HeapRegion* region_at(size_t idx);

   869 

   870 

   871   // Divide the heap region sequence into "chunks" of some size (the number

   872   // of regions divided by the number of parallel threads times some

   873   // overpartition factor, currently 4).  Assumes that this will be called

   874   // in parallel by ParallelGCThreads worker threads with discinct worker

   875   // ids in the range [0..max(ParallelGCThreads-1, 1)], that all parallel

   876   // calls will use the same "claim_value", and that that claim value is

   877   // different from the claim_value of any heap region before the start of

   878   // the iteration.  Applies "blk->doHeapRegion" to each of the regions, by

   879   // attempting to claim the first region in each chunk, and, if

   880   // successful, applying the closure to each region in the chunk (and

   881   // setting the claim value of the second and subsequent regions of the

   882   // chunk.)  For now requires that "doHeapRegion" always returns "false",

   883   // i.e., that a closure never attempt to abort a traversal.

   884   void heap_region_par_iterate_chunked(HeapRegionClosure* blk,

   885                                        int worker,

   886                                        jint claim_value);

   887 

   888   // Iterate over the regions (if any) in the current collection set.

   889   void collection_set_iterate(HeapRegionClosure* blk);

   890 

   891   // As above but starting from region r

   892   void collection_set_iterate_from(HeapRegion* r, HeapRegionClosure *blk);

   893 

   894   // Returns the first (lowest address) compactible space in the heap.

   895   virtual CompactibleSpace* first_compactible_space();

   896 

   897   // A CollectedHeap will contain some number of spaces.  This finds the

   898   // space containing a given address, or else returns NULL.

   899   virtual Space* space_containing(const void* addr) const;

   900 

   901   // A G1CollectedHeap will contain some number of heap regions.  This

   902   // finds the region containing a given address, or else returns NULL.

   903   HeapRegion* heap_region_containing(const void* addr) const;

   904 

   905   // Like the above, but requires "addr" to be in the heap (to avoid a

   906   // null-check), and unlike the above, may return an continuing humongous

   907   // region.

   908   HeapRegion* heap_region_containing_raw(const void* addr) const;

   909 

   910   // A CollectedHeap is divided into a dense sequence of "blocks"; that is,

   911   // each address in the (reserved) heap is a member of exactly

   912   // one block.  The defining characteristic of a block is that it is

   913   // possible to find its size, and thus to progress forward to the next

   914   // block.  (Blocks may be of different sizes.)  Thus, blocks may

   915   // represent Java objects, or they might be free blocks in a

   916   // free-list-based heap (or subheap), as long as the two kinds are

   917   // distinguishable and the size of each is determinable.

   918 

   919   // Returns the address of the start of the "block" that contains the

   920   // address "addr".  We say "blocks" instead of "object" since some heaps

   921   // may not pack objects densely; a chunk may either be an object or a

   922   // non-object.

   923   virtual HeapWord* block_start(const void* addr) const;

   924 

   925   // Requires "addr" to be the start of a chunk, and returns its size.

   926   // "addr + size" is required to be the start of a new chunk, or the end

   927   // of the active area of the heap.

   928   virtual size_t block_size(const HeapWord* addr) const;

   929 

   930   // Requires "addr" to be the start of a block, and returns "TRUE" iff

   931   // the block is an object.

   932   virtual bool block_is_obj(const HeapWord* addr) const;

   933 

   934   // Does this heap support heap inspection? (+PrintClassHistogram)

   935   virtual bool supports_heap_inspection() const { return true; }

   936 

   937   // Section on thread-local allocation buffers (TLABs)

   938   // See CollectedHeap for semantics.

   939 

   940   virtual bool supports_tlab_allocation() const;

   941   virtual size_t tlab_capacity(Thread* thr) const;

   942   virtual size_t unsafe_max_tlab_alloc(Thread* thr) const;

   943   virtual HeapWord* allocate_new_tlab(size_t size);

   944 

   945   // Can a compiler initialize a new object without store barriers?

   946   // This permission only extends from the creation of a new object

   947   // via a TLAB up to the first subsequent safepoint.

   948   virtual bool can_elide_tlab_store_barriers() const {

   949     // Since G1's TLAB's may, on occasion, come from non-young regions

   950     // as well. (Is there a flag controlling that? XXX)

   951     return false;

   952   }

   953 

   954   // Can a compiler elide a store barrier when it writes

   955   // a permanent oop into the heap?  Applies when the compiler

   956   // is storing x to the heap, where x->is_perm() is true.

   957   virtual bool can_elide_permanent_oop_store_barriers() const {

   958     // At least until perm gen collection is also G1-ified, at

   959     // which point this should return false.

   960     return true;

   961   }

   962 

   963   virtual bool allocs_are_zero_filled();

   964 

   965   // The boundary between a "large" and "small" array of primitives, in

   966   // words.

   967   virtual size_t large_typearray_limit();

   968 

   969   // All popular objects are guaranteed to have addresses below this

   970   // boundary.

   971   HeapWord* popular_object_boundary() {

   972     return _popular_object_boundary;

   973   }

   974 

   975   // Declare the region as one that should be evacuated because its

   976   // remembered set is too large.

   977   void schedule_popular_region_evac(HeapRegion* r);

   978   // If there is a popular region to evacuate it, remove it from the list

   979   // and return it.

   980   HeapRegion* popular_region_to_evac();

   981   // Evacuate the given popular region.

   982   void evac_popular_region(HeapRegion* r);

   983 

   984   // Returns "true" iff the given word_size is "very large".

   985   static bool isHumongous(size_t word_size) {

   986     return word_size >= VeryLargeInWords;

   987   }

   988 

   989   // Update mod union table with the set of dirty cards.

   990   void updateModUnion();

   991 

   992   // Set the mod union bits corresponding to the given memRegion.  Note

   993   // that this is always a safe operation, since it doesn't clear any

   994   // bits.

   995   void markModUnionRange(MemRegion mr);

   996 

   997   // Records the fact that a marking phase is no longer in progress.

   998   void set_marking_complete() {

   999     _mark_in_progress = false;

  1000   }

  1001   void set_marking_started() {

  1002     _mark_in_progress = true;

  1003   }

  1004   bool mark_in_progress() {

  1005     return _mark_in_progress;

  1006   }

  1007 

  1008   // Print the maximum heap capacity.

  1009   virtual size_t max_capacity() const;

  1010 

  1011   virtual jlong millis_since_last_gc();

  1012 

  1013   // Perform any cleanup actions necessary before allowing a verification.

  1014   virtual void prepare_for_verify();

  1015 

  1016   // Perform verification.

  1017   virtual void verify(bool allow_dirty, bool silent);

  1018   virtual void print() const;

  1019   virtual void print_on(outputStream* st) const;

  1020 

  1021   virtual void print_gc_threads_on(outputStream* st) const;

  1022   virtual void gc_threads_do(ThreadClosure* tc) const;

  1023 

  1024   // Override

  1025   void print_tracing_info() const;

  1026 

  1027   // If "addr" is a pointer into the (reserved?) heap, returns a positive

  1028   // number indicating the "arena" within the heap in which "addr" falls.

  1029   // Or else returns 0.

  1030   virtual int addr_to_arena_id(void* addr) const;

  1031 

  1032   // Convenience function to be used in situations where the heap type can be

  1033   // asserted to be this type.

  1034   static G1CollectedHeap* heap();

  1035 

  1036   void empty_young_list();

  1037   bool should_set_young_locked();

  1038 

  1039   void set_region_short_lived_locked(HeapRegion* hr);

  1040   // add appropriate methods for any other surv rate groups

  1041 

  1042   void young_list_rs_length_sampling_init() {

  1043     _young_list->rs_length_sampling_init();

  1044   }

  1045   bool young_list_rs_length_sampling_more() {

  1046     return _young_list->rs_length_sampling_more();

  1047   }

  1048   void young_list_rs_length_sampling_next() {

  1049     _young_list->rs_length_sampling_next();

  1050   }

  1051   size_t young_list_sampled_rs_lengths() {

  1052     return _young_list->sampled_rs_lengths();

  1053   }

  1054 

  1055   size_t young_list_length()   { return _young_list->length(); }

  1056   size_t young_list_scan_only_length() {

  1057                                       return _young_list->scan_only_length(); }

  1058 

  1059   HeapRegion* pop_region_from_young_list() {

  1060     return _young_list->pop_region();

  1061   }

  1062 

  1063   HeapRegion* young_list_first_region() {

  1064     return _young_list->first_region();

  1065   }

  1066 

  1067   // debugging

  1068   bool check_young_list_well_formed() {

  1069     return _young_list->check_list_well_formed();

  1070   }

  1071   bool check_young_list_empty(bool ignore_scan_only_list,

  1072                               bool check_sample = true);

  1073 

  1074   // *** Stuff related to concurrent marking.  It's not clear to me that so

  1075   // many of these need to be public.

  1076 

  1077   // The functions below are helper functions that a subclass of

  1078   // "CollectedHeap" can use in the implementation of its virtual

  1079   // functions.

  1080   // This performs a concurrent marking of the live objects in a

  1081   // bitmap off to the side.

  1082   void doConcurrentMark();

  1083 

  1084   // This is called from the marksweep collector which then does

  1085   // a concurrent mark and verifies that the results agree with

  1086   // the stop the world marking.

  1087   void checkConcurrentMark();

  1088   void do_sync_mark();

  1089 

  1090   bool isMarkedPrev(oop obj) const;

  1091   bool isMarkedNext(oop obj) const;

  1092 

  1093   // Determine if an object is dead, given the object and also

  1094   // the region to which the object belongs. An object is dead

  1095   // iff a) it was not allocated since the last mark and b) it

  1096   // is not marked.

  1097 

  1098   bool is_obj_dead(const oop obj, const HeapRegion* hr) const {

  1099     return

  1100       !hr->obj_allocated_since_prev_marking(obj) &&

  1101       !isMarkedPrev(obj);

  1102   }

  1103 

  1104   // This is used when copying an object to survivor space.

  1105   // If the object is marked live, then we mark the copy live.

  1106   // If the object is allocated since the start of this mark

  1107   // cycle, then we mark the copy live.

  1108   // If the object has been around since the previous mark

  1109   // phase, and hasn't been marked yet during this phase,

  1110   // then we don't mark it, we just wait for the

  1111   // current marking cycle to get to it.

  1112 

  1113   // This function returns true when an object has been

  1114   // around since the previous marking and hasn't yet

  1115   // been marked during this marking.

  1116 

  1117   bool is_obj_ill(const oop obj, const HeapRegion* hr) const {

  1118     return

  1119       !hr->obj_allocated_since_next_marking(obj) &&

  1120       !isMarkedNext(obj);

  1121   }

  1122 

  1123   // Determine if an object is dead, given only the object itself.

  1124   // This will find the region to which the object belongs and

  1125   // then call the region version of the same function.

  1126 

  1127   // Added if it is in permanent gen it isn't dead.

  1128   // Added if it is NULL it isn't dead.

  1129 

  1130   bool is_obj_dead(oop obj) {

  1131     HeapRegion* hr = heap_region_containing(obj);

  1132     if (hr == NULL) {

  1133       if (Universe::heap()->is_in_permanent(obj))

  1134         return false;

  1135       else if (obj == NULL) return false;