1 /*

     2  * Copyright (c) 2001, 2017, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  *

    23  */

    24 

    25 #ifndef SHARE_VM_GC_G1_G1CONCURRENTMARK_HPP

    26 #define SHARE_VM_GC_G1_G1CONCURRENTMARK_HPP

    27 

    28 #include "classfile/javaClasses.hpp"

    29 #include "gc/g1/g1ConcurrentMarkBitMap.hpp"

    30 #include "gc/g1/g1ConcurrentMarkObjArrayProcessor.hpp"

    31 #include "gc/g1/g1RegionToSpaceMapper.hpp"

    32 #include "gc/g1/heapRegionSet.hpp"

    33 #include "gc/shared/taskqueue.hpp"

    34 

    35 class G1CollectedHeap;

    36 class G1CMTask;

    37 class G1ConcurrentMark;

    38 class ConcurrentGCTimer;

    39 class G1OldTracer;

    40 class G1SurvivorRegions;

    41 

    42 #ifdef _MSC_VER

    43 #pragma warning(push)

    44 // warning C4522: multiple assignment operators specified

    45 #pragma warning(disable:4522)

    46 #endif

    47 

    48 // This is a container class for either an oop or a continuation address for

    49 // mark stack entries. Both are pushed onto the mark stack.

    50 class G1TaskQueueEntry VALUE_OBJ_CLASS_SPEC {

    51 private:

    52   void* _holder;

    53 

    54   static const uintptr_t ArraySliceBit = 1;

    55 

    56   G1TaskQueueEntry(oop obj) : _holder(obj) {

    57     assert(_holder != NULL, "Not allowed to set NULL task queue element");

    58   }

    59   G1TaskQueueEntry(HeapWord* addr) : _holder((void*)((uintptr_t)addr | ArraySliceBit)) { }

    60 public:

    61   G1TaskQueueEntry(const G1TaskQueueEntry& other) { _holder = other._holder; }

    62   G1TaskQueueEntry() : _holder(NULL) { }

    63 

    64   static G1TaskQueueEntry from_slice(HeapWord* what) { return G1TaskQueueEntry(what); }

    65   static G1TaskQueueEntry from_oop(oop obj) { return G1TaskQueueEntry(obj); }

    66 

    67   G1TaskQueueEntry& operator=(const G1TaskQueueEntry& t) {

    68     _holder = t._holder;

    69     return *this;

    70   }

    71 

    72   volatile G1TaskQueueEntry& operator=(const volatile G1TaskQueueEntry& t) volatile {

    73     _holder = t._holder;

    74     return *this;

    75   }

    76 

    77   oop obj() const {

    78     assert(!is_array_slice(), "Trying to read array slice " PTR_FORMAT " as oop", p2i(_holder));

    79     return (oop)_holder;

    80   }

    81 

    82   HeapWord* slice() const {

    83     assert(is_array_slice(), "Trying to read oop " PTR_FORMAT " as array slice", p2i(_holder));

    84     return (HeapWord*)((uintptr_t)_holder & ~ArraySliceBit);

    85   }

    86 

    87   bool is_oop() const { return !is_array_slice(); }

    88   bool is_array_slice() const { return ((uintptr_t)_holder & ArraySliceBit) != 0; }

    89   bool is_null() const { return _holder == NULL; }

    90 };

    91 

    92 #ifdef _MSC_VER

    93 #pragma warning(pop)

    94 #endif

    95 

    96 typedef GenericTaskQueue<G1TaskQueueEntry, mtGC> G1CMTaskQueue;

    97 typedef GenericTaskQueueSet<G1CMTaskQueue, mtGC> G1CMTaskQueueSet;

    98 

    99 // Closure used by CM during concurrent reference discovery

   100 // and reference processing (during remarking) to determine

   101 // if a particular object is alive. It is primarily used

   102 // to determine if referents of discovered reference objects

   103 // are alive. An instance is also embedded into the

   104 // reference processor as the _is_alive_non_header field

   105 class G1CMIsAliveClosure: public BoolObjectClosure {

   106   G1CollectedHeap* _g1;

   107  public:

   108   G1CMIsAliveClosure(G1CollectedHeap* g1) : _g1(g1) { }

   109 

   110   bool do_object_b(oop obj);

   111 };

   112 

   113 // Represents the overflow mark stack used by concurrent marking.

   114 //

   115 // Stores oops in a huge buffer in virtual memory that is always fully committed.

   116 // Resizing may only happen during a STW pause when the stack is empty.

   117 //

   118 // Memory is allocated on a "chunk" basis, i.e. a set of oops. For this, the mark

   119 // stack memory is split into evenly sized chunks of oops. Users can only

   120 // add or remove entries on that basis.

   121 // Chunks are filled in increasing address order. Not completely filled chunks

   122 // have a NULL element as a terminating element.

   123 //

   124 // Every chunk has a header containing a single pointer element used for memory

   125 // management. This wastes some space, but is negligible (< .1% with current sizing).

   126 //

   127 // Memory management is done using a mix of tracking a high water-mark indicating

   128 // that all chunks at a lower address are valid chunks, and a singly linked free

   129 // list connecting all empty chunks.

   130 class G1CMMarkStack VALUE_OBJ_CLASS_SPEC {

   131 public:

   132   // Number of TaskQueueEntries that can fit in a single chunk.

   133   static const size_t EntriesPerChunk = 1024 - 1 /* One reference for the next pointer */;

   134 private:

   135   struct TaskQueueEntryChunk {

   136     TaskQueueEntryChunk* next;

   137     G1TaskQueueEntry data[EntriesPerChunk];

   138   };

   139 

   140   size_t _max_chunk_capacity;    // Maximum number of TaskQueueEntryChunk elements on the stack.

   141 

   142   TaskQueueEntryChunk* _base;    // Bottom address of allocated memory area.

   143   size_t _chunk_capacity;        // Current maximum number of TaskQueueEntryChunk elements.

   144 

   145   char _pad0[DEFAULT_CACHE_LINE_SIZE];

   146   TaskQueueEntryChunk* volatile _free_list;  // Linked list of free chunks that can be allocated by users.

   147   char _pad1[DEFAULT_CACHE_LINE_SIZE - sizeof(TaskQueueEntryChunk*)];

   148   TaskQueueEntryChunk* volatile _chunk_list; // List of chunks currently containing data.

   149   volatile size_t _chunks_in_chunk_list;

   150   char _pad2[DEFAULT_CACHE_LINE_SIZE - sizeof(TaskQueueEntryChunk*) - sizeof(size_t)];

   151 

   152   volatile size_t _hwm;          // High water mark within the reserved space.

   153   char _pad4[DEFAULT_CACHE_LINE_SIZE - sizeof(size_t)];

   154 

   155   // Allocate a new chunk from the reserved memory, using the high water mark. Returns

   156   // NULL if out of memory.

   157   TaskQueueEntryChunk* allocate_new_chunk();

   158 

   159   // Atomically add the given chunk to the list.

   160   void add_chunk_to_list(TaskQueueEntryChunk* volatile* list, TaskQueueEntryChunk* elem);

   161   // Atomically remove and return a chunk from the given list. Returns NULL if the

   162   // list is empty.

   163   TaskQueueEntryChunk* remove_chunk_from_list(TaskQueueEntryChunk* volatile* list);

   164 

   165   void add_chunk_to_chunk_list(TaskQueueEntryChunk* elem);

   166   void add_chunk_to_free_list(TaskQueueEntryChunk* elem);

   167 

   168   TaskQueueEntryChunk* remove_chunk_from_chunk_list();

   169   TaskQueueEntryChunk* remove_chunk_from_free_list();

   170 

   171   // Resizes the mark stack to the given new capacity. Releases any previous

   172   // memory if successful.

   173   bool resize(size_t new_capacity);

   174 

   175  public:

   176   G1CMMarkStack();

   177   ~G1CMMarkStack();

   178 

   179   // Alignment and minimum capacity of this mark stack in number of oops.

   180   static size_t capacity_alignment();

   181 

   182   // Allocate and initialize the mark stack with the given number of oops.

   183   bool initialize(size_t initial_capacity, size_t max_capacity);

   184 

   185   // Pushes the given buffer containing at most EntriesPerChunk elements on the mark

   186   // stack. If less than EntriesPerChunk elements are to be pushed, the array must

   187   // be terminated with a NULL.

   188   // Returns whether the buffer contents were successfully pushed to the global mark

   189   // stack.

   190   bool par_push_chunk(G1TaskQueueEntry* buffer);

   191 

   192   // Pops a chunk from this mark stack, copying them into the given buffer. This

   193   // chunk may contain up to EntriesPerChunk elements. If there are less, the last

   194   // element in the array is a NULL pointer.

   195   bool par_pop_chunk(G1TaskQueueEntry* buffer);

   196 

   197   // Return whether the chunk list is empty. Racy due to unsynchronized access to

   198   // _chunk_list.

   199   bool is_empty() const { return _chunk_list == NULL; }

   200 

   201   size_t capacity() const  { return _chunk_capacity; }

   202 

   203   // Expand the stack, typically in response to an overflow condition

   204   void expand();

   205 

   206   // Return the approximate number of oops on this mark stack. Racy due to

   207   // unsynchronized access to _chunks_in_chunk_list.

   208   size_t size() const { return _chunks_in_chunk_list * EntriesPerChunk; }

   209 

   210   void set_empty();

   211 

   212   // Apply Fn to every oop on the mark stack. The mark stack must not

   213   // be modified while iterating.

   214   template<typename Fn> void iterate(Fn fn) const PRODUCT_RETURN;

   215 };

   216 

   217 // Root Regions are regions that are not empty at the beginning of a

   218 // marking cycle and which we might collect during an evacuation pause

   219 // while the cycle is active. Given that, during evacuation pauses, we

   220 // do not copy objects that are explicitly marked, what we have to do

   221 // for the root regions is to scan them and mark all objects reachable

   222 // from them. According to the SATB assumptions, we only need to visit

   223 // each object once during marking. So, as long as we finish this scan

   224 // before the next evacuation pause, we can copy the objects from the

   225 // root regions without having to mark them or do anything else to them.

   226 //

   227 // Currently, we only support root region scanning once (at the start

   228 // of the marking cycle) and the root regions are all the survivor

   229 // regions populated during the initial-mark pause.

   230 class G1CMRootRegions VALUE_OBJ_CLASS_SPEC {

   231 private:

   232   const G1SurvivorRegions* _survivors;

   233   G1ConcurrentMark*        _cm;

   234 

   235   volatile bool            _scan_in_progress;

   236   volatile bool            _should_abort;

   237   volatile int             _claimed_survivor_index;

   238 

   239   void notify_scan_done();

   240 

   241 public:

   242   G1CMRootRegions();

   243   // We actually do most of the initialization in this method.

   244   void init(const G1SurvivorRegions* survivors, G1ConcurrentMark* cm);

   245 

   246   // Reset the claiming / scanning of the root regions.

   247   void prepare_for_scan();

   248 

   249   // Forces get_next() to return NULL so that the iteration aborts early.

   250   void abort() { _should_abort = true; }

   251 

   252   // Return true if the CM thread are actively scanning root regions,

   253   // false otherwise.

   254   bool scan_in_progress() { return _scan_in_progress; }

   255 

   256   // Claim the next root region to scan atomically, or return NULL if

   257   // all have been claimed.

   258   HeapRegion* claim_next();

   259 

   260   // The number of root regions to scan.

   261   uint num_root_regions() const;

   262 

   263   void cancel_scan();

   264 

   265   // Flag that we're done with root region scanning and notify anyone

   266   // who's waiting on it. If aborted is false, assume that all regions

   267   // have been claimed.

   268   void scan_finished();

   269 

   270   // If CM threads are still scanning root regions, wait until they

   271   // are done. Return true if we had to wait, false otherwise.

   272   bool wait_until_scan_finished();

   273 };

   274 

   275 class ConcurrentMarkThread;

   276 

   277 class G1ConcurrentMark: public CHeapObj<mtGC> {

   278   friend class ConcurrentMarkThread;

   279   friend class G1ParNoteEndTask;

   280   friend class G1VerifyLiveDataClosure;

   281   friend class G1CMRefProcTaskProxy;

   282   friend class G1CMRefProcTaskExecutor;

   283   friend class G1CMKeepAliveAndDrainClosure;

   284   friend class G1CMDrainMarkingStackClosure;

   285   friend class G1CMBitMapClosure;

   286   friend class G1CMConcurrentMarkingTask;

   287   friend class G1CMRemarkTask;

   288   friend class G1CMTask;

   289 

   290 protected:

   291   ConcurrentMarkThread* _cmThread;   // The thread doing the work

   292   G1CollectedHeap*      _g1h;        // The heap

   293   uint                  _parallel_marking_threads; // The number of marking

   294                                                    // threads we're using

   295   uint                  _max_parallel_marking_threads; // Max number of marking

   296                                                        // threads we'll ever use

   297   double                _sleep_factor; // How much we have to sleep, with

   298                                        // respect to the work we just did, to

   299                                        // meet the marking overhead goal

   300   double                _marking_task_overhead; // Marking target overhead for

   301                                                 // a single task

   302 

   303   FreeRegionList        _cleanup_list;

   304 

   305   // Concurrent marking support structures

   306   G1CMBitMap              _markBitMap1;

   307   G1CMBitMap              _markBitMap2;

   308   G1CMBitMap*             _prevMarkBitMap; // Completed mark bitmap

   309   G1CMBitMap*             _nextMarkBitMap; // Under-construction mark bitmap

   310 

   311   // Heap bounds

   312   HeapWord*               _heap_start;

   313   HeapWord*               _heap_end;

   314 

   315   // Root region tracking and claiming

   316   G1CMRootRegions         _root_regions;

   317 

   318   // For gray objects

   319   G1CMMarkStack           _global_mark_stack; // Grey objects behind global finger

   320   HeapWord* volatile      _finger;  // The global finger, region aligned,

   321                                     // always points to the end of the

   322                                     // last claimed region

   323 

   324   // Marking tasks

   325   uint                    _max_worker_id;// Maximum worker id

   326   uint                    _active_tasks; // Task num currently active

   327   G1CMTask**              _tasks;        // Task queue array (max_worker_id len)

   328   G1CMTaskQueueSet*       _task_queues;  // Task queue set

   329   ParallelTaskTerminator  _terminator;   // For termination

   330 

   331   // Two sync barriers that are used to synchronize tasks when an

   332   // overflow occurs. The algorithm is the following. All tasks enter

   333   // the first one to ensure that they have all stopped manipulating

   334   // the global data structures. After they exit it, they re-initialize

   335   // their data structures and task 0 re-initializes the global data

   336   // structures. Then, they enter the second sync barrier. This

   337   // ensure, that no task starts doing work before all data

   338   // structures (local and global) have been re-initialized. When they

   339   // exit it, they are free to start working again.

   340   WorkGangBarrierSync     _first_overflow_barrier_sync;

   341   WorkGangBarrierSync     _second_overflow_barrier_sync;

   342 

   343   // This is set by any task, when an overflow on the global data

   344   // structures is detected

   345   volatile bool           _has_overflown;

   346   // True: marking is concurrent, false: we're in remark

   347   volatile bool           _concurrent;

   348   // Set at the end of a Full GC so that marking aborts

   349   volatile bool           _has_aborted;

   350 

   351   // Used when remark aborts due to an overflow to indicate that

   352   // another concurrent marking phase should start

   353   volatile bool           _restart_for_overflow;

   354 

   355   // This is true from the very start of concurrent marking until the

   356   // point when all the tasks complete their work. It is really used

   357   // to determine the points between the end of concurrent marking and

   358   // time of remark.

   359   volatile bool           _concurrent_marking_in_progress;

   360 

   361   ConcurrentGCTimer*      _gc_timer_cm;

   362 

   363   G1OldTracer*            _gc_tracer_cm;

   364 

   365   // All of these times are in ms

   366   NumberSeq _init_times;

   367   NumberSeq _remark_times;

   368   NumberSeq _remark_mark_times;

   369   NumberSeq _remark_weak_ref_times;

   370   NumberSeq _cleanup_times;

   371   double    _total_counting_time;

   372   double    _total_rs_scrub_time;

   373 

   374   double*   _accum_task_vtime;   // Accumulated task vtime

   375 

   376   WorkGang* _parallel_workers;

   377 

   378   void weakRefsWorkParallelPart(BoolObjectClosure* is_alive, bool purged_classes);

   379   void weakRefsWork(bool clear_all_soft_refs);

   380 

   381   void swapMarkBitMaps();

   382 

   383   // It resets the global marking data structures, as well as the

   384   // task local ones; should be called during initial mark.

   385   void reset();

   386 

   387   // Resets all the marking data structures. Called when we have to restart

   388   // marking or when marking completes (via set_non_marking_state below).

   389   void reset_marking_state();

   390 

   391   // We do this after we're done with marking so that the marking data

   392   // structures are initialized to a sensible and predictable state.

   393   void set_non_marking_state();

   394 

   395   // Called to indicate how many threads are currently active.

   396   void set_concurrency(uint active_tasks);

   397 

   398   // It should be called to indicate which phase we're in (concurrent

   399   // mark or remark) and how many threads are currently active.

   400   void set_concurrency_and_phase(uint active_tasks, bool concurrent);

   401 

   402   // Prints all gathered CM-related statistics

   403   void print_stats();

   404 

   405   bool cleanup_list_is_empty() {

   406     return _cleanup_list.is_empty();

   407   }

   408 

   409   // Accessor methods

   410   uint parallel_marking_threads() const     { return _parallel_marking_threads; }

   411   uint max_parallel_marking_threads() const { return _max_parallel_marking_threads;}

   412   double sleep_factor()                     { return _sleep_factor; }

   413   double marking_task_overhead()            { return _marking_task_overhead;}

   414 

   415   HeapWord*               finger()          { return _finger;   }

   416   bool                    concurrent()      { return _concurrent; }

   417   uint                    active_tasks()    { return _active_tasks; }

   418   ParallelTaskTerminator* terminator()      { return &_terminator; }

   419 

   420   // It claims the next available region to be scanned by a marking

   421   // task/thread. It might return NULL if the next region is empty or

   422   // we have run out of regions. In the latter case, out_of_regions()

   423   // determines whether we've really run out of regions or the task

   424   // should call claim_region() again. This might seem a bit

   425   // awkward. Originally, the code was written so that claim_region()

   426   // either successfully returned with a non-empty region or there

   427   // were no more regions to be claimed. The problem with this was

   428   // that, in certain circumstances, it iterated over large chunks of

   429   // the heap finding only empty regions and, while it was working, it

   430   // was preventing the calling task to call its regular clock

   431   // method. So, this way, each task will spend very little time in

   432   // claim_region() and is allowed to call the regular clock method

   433   // frequently.

   434   HeapRegion* claim_region(uint worker_id);

   435 

   436   // It determines whether we've run out of regions to scan. Note that

   437   // the finger can point past the heap end in case the heap was expanded

   438   // to satisfy an allocation without doing a GC. This is fine, because all

   439   // objects in those regions will be considered live anyway because of

   440   // SATB guarantees (i.e. their TAMS will be equal to bottom).

   441   bool        out_of_regions() { return _finger >= _heap_end; }

   442 

   443   // Returns the task with the given id

   444   G1CMTask* task(int id) {

   445     assert(0 <= id && id < (int) _active_tasks,

   446            "task id not within active bounds");

   447     return _tasks[id];

   448   }

   449 

   450   // Returns the task queue with the given id

   451   G1CMTaskQueue* task_queue(int id) {

   452     assert(0 <= id && id < (int) _active_tasks,

   453            "task queue id not within active bounds");

   454     return (G1CMTaskQueue*) _task_queues->queue(id);

   455   }

   456 

   457   // Returns the task queue set

   458   G1CMTaskQueueSet* task_queues()  { return _task_queues; }

   459 

   460   // Access / manipulation of the overflow flag which is set to

   461   // indicate that the global stack has overflown

   462   bool has_overflown()           { return _has_overflown; }

   463   void set_has_overflown()       { _has_overflown = true; }

   464   void clear_has_overflown()     { _has_overflown = false; }

   465   bool restart_for_overflow()    { return _restart_for_overflow; }

   466 

   467   // Methods to enter the two overflow sync barriers

   468   void enter_first_sync_barrier(uint worker_id);

   469   void enter_second_sync_barrier(uint worker_id);

   470 

   471   // Card index of the bottom of the G1 heap. Used for biasing indices into

   472   // the card bitmaps.

   473   intptr_t _heap_bottom_card_num;

   474 

   475   // Set to true when initialization is complete

   476   bool _completed_initialization;

   477 

   478   // end_timer, true to end gc timer after ending concurrent phase.

   479   void register_concurrent_phase_end_common(bool end_timer);

   480 

   481   // Clear the given bitmap in parallel using the given WorkGang. If may_yield is

   482   // true, periodically insert checks to see if this method should exit prematurely.

   483   void clear_bitmap(G1CMBitMap* bitmap, WorkGang* workers, bool may_yield);

   484 public:

   485   // Manipulation of the global mark stack.

   486   // The push and pop operations are used by tasks for transfers

   487   // between task-local queues and the global mark stack.

   488   bool mark_stack_push(G1TaskQueueEntry* arr) {

   489     if (!_global_mark_stack.par_push_chunk(arr)) {

   490       set_has_overflown();

   491       return false;

   492     }

   493     return true;

   494   }

   495   bool mark_stack_pop(G1TaskQueueEntry* arr) {

   496     return _global_mark_stack.par_pop_chunk(arr);

   497   }

   498   size_t mark_stack_size()                { return _global_mark_stack.size(); }

   499   size_t partial_mark_stack_size_target() { return _global_mark_stack.capacity()/3; }

   500   bool mark_stack_empty()                 { return _global_mark_stack.is_empty(); }

   501 

   502   G1CMRootRegions* root_regions() { return &_root_regions; }

   503 

   504   bool concurrent_marking_in_progress() {

   505     return _concurrent_marking_in_progress;

   506   }

   507   void set_concurrent_marking_in_progress() {

   508     _concurrent_marking_in_progress = true;

   509   }

   510   void clear_concurrent_marking_in_progress() {

   511     _concurrent_marking_in_progress = false;

   512   }

   513 

   514   void concurrent_cycle_start();

   515   void concurrent_cycle_end();

   516 

   517   void update_accum_task_vtime(int i, double vtime) {

   518     _accum_task_vtime[i] += vtime;

   519   }

   520 

   521   double all_task_accum_vtime() {

   522     double ret = 0.0;

   523     for (uint i = 0; i < _max_worker_id; ++i)

   524       ret += _accum_task_vtime[i];

   525     return ret;

   526   }

   527 

   528   // Attempts to steal an object from the task queues of other tasks

   529   bool try_stealing(uint worker_id, int* hash_seed, G1TaskQueueEntry& task_entry);

   530 

   531   G1ConcurrentMark(G1CollectedHeap* g1h,

   532                    G1RegionToSpaceMapper* prev_bitmap_storage,

   533                    G1RegionToSpaceMapper* next_bitmap_storage);

   534   ~G1ConcurrentMark();

   535 

   536   ConcurrentMarkThread* cmThread() { return _cmThread; }

   537 

   538   const G1CMBitMap* const prevMarkBitMap() const { return _prevMarkBitMap; }

   539   G1CMBitMap* nextMarkBitMap() const { return _nextMarkBitMap; }

   540 

   541   // Returns the number of GC threads to be used in a concurrent

   542   // phase based on the number of GC threads being used in a STW

   543   // phase.

   544   uint scale_parallel_threads(uint n_par_threads);

   545 

   546   // Calculates the number of GC threads to be used in a concurrent phase.

   547   uint calc_parallel_marking_threads();

   548 

   549   // Prepare internal data structures for the next mark cycle. This includes clearing

   550   // the next mark bitmap and some internal data structures. This method is intended

   551   // to be called concurrently to the mutator. It will yield to safepoint requests.

   552   void cleanup_for_next_mark();

   553 

   554   // Clear the previous marking bitmap during safepoint.

   555   void clear_prev_bitmap(WorkGang* workers);

   556 

   557   // Return whether the next mark bitmap has no marks set. To be used for assertions

   558   // only. Will not yield to pause requests.

   559   bool nextMarkBitmapIsClear();

   560 

   561   // These two do the work that needs to be done before and after the

   562   // initial root checkpoint. Since this checkpoint can be done at two

   563   // different points (i.e. an explicit pause or piggy-backed on a

   564   // young collection), then it's nice to be able to easily share the

   565   // pre/post code. It might be the case that we can put everything in

   566   // the post method. TP

   567   void checkpointRootsInitialPre();

   568   void checkpointRootsInitialPost();

   569 

   570   // Scan all the root regions and mark everything reachable from

   571   // them.

   572   void scan_root_regions();

   573 

   574   // Scan a single root region and mark everything reachable from it.

   575   void scanRootRegion(HeapRegion* hr);

   576 

   577   // Do concurrent phase of marking, to a tentative transitive closure.

   578   void mark_from_roots();

   579 

   580   void checkpointRootsFinal(bool clear_all_soft_refs);

   581   void checkpointRootsFinalWork();

   582   void cleanup();

   583   void complete_cleanup();

   584 

   585   // Mark in the previous bitmap.  NB: this is usually read-only, so use

   586   // this carefully!

   587   inline void markPrev(oop p);

   588 

   589   // Clears marks for all objects in the given range, for the prev or

   590   // next bitmaps.  NB: the previous bitmap is usually

   591   // read-only, so use this carefully!

   592   void clearRangePrevBitmap(MemRegion mr);

   593 

   594   // Verify that there are no CSet oops on the stacks (taskqueues /

   595   // global mark stack) and fingers (global / per-task).

   596   // If marking is not in progress, it's a no-op.

   597   void verify_no_cset_oops() PRODUCT_RETURN;

   598 

   599   inline bool isPrevMarked(oop p) const;

   600 

   601   inline bool do_yield_check();

   602 

   603   // Abandon current marking iteration due to a Full GC.

   604   void abort();

   605 

   606   bool has_aborted()      { return _has_aborted; }

   607 

   608   void print_summary_info();

   609 

   610   void print_worker_threads_on(outputStream* st) const;

   611   void threads_do(ThreadClosure* tc) const;

   612 

   613   void print_on_error(outputStream* st) const;

   614 

   615   // Mark the given object on the next bitmap if it is below nTAMS.

   616   inline bool mark_in_next_bitmap(HeapRegion* const hr, oop const obj);

   617   inline bool mark_in_next_bitmap(oop const obj);

   618 

   619   // Returns true if initialization was successfully completed.

   620   bool completed_initialization() const {

   621     return _completed_initialization;

   622   }

   623 

   624   ConcurrentGCTimer* gc_timer_cm() const { return _gc_timer_cm; }

   625   G1OldTracer* gc_tracer_cm() const { return _gc_tracer_cm; }

   626 

   627 private:

   628   // Clear (Reset) all liveness count data.

   629   void clear_live_data(WorkGang* workers);

   630 

   631 #ifdef ASSERT

   632   // Verify all of the above data structures that they are in initial state.

   633   void verify_live_data_clear();

   634 #endif

   635 

   636   // Aggregates the per-card liveness data based on the current marking. Also sets

   637   // the amount of marked bytes for each region.

   638   void create_live_data();

   639 

   640   void finalize_live_data();

   641 

   642   void verify_live_data();

   643 };

   644 

   645 // A class representing a marking task.

   646 class G1CMTask : public TerminatorTerminator {

   647 private:

   648   enum PrivateConstants {

   649     // The regular clock call is called once the scanned words reaches

   650     // this limit

   651     words_scanned_period          = 12*1024,

   652     // The regular clock call is called once the number of visited

   653     // references reaches this limit

   654     refs_reached_period           = 1024,

   655     // Initial value for the hash seed, used in the work stealing code

   656     init_hash_seed                = 17

   657   };

   658 

   659   G1CMObjArrayProcessor       _objArray_processor;

   660 

   661   uint                        _worker_id;

   662   G1CollectedHeap*            _g1h;

   663   G1ConcurrentMark*           _cm;

   664   G1CMBitMap*                 _nextMarkBitMap;

   665   // the task queue of this task

   666   G1CMTaskQueue*              _task_queue;

   667 private:

   668   // the task queue set---needed for stealing

   669   G1CMTaskQueueSet*           _task_queues;

   670   // indicates whether the task has been claimed---this is only  for

   671   // debugging purposes

   672   bool                        _claimed;

   673 

   674   // number of calls to this task

   675   int                         _calls;

   676 

   677   // when the virtual timer reaches this time, the marking step should

   678   // exit

   679   double                      _time_target_ms;

   680   // the start time of the current marking step

   681   double                      _start_time_ms;

   682 

   683   // the oop closure used for iterations over oops

   684   G1CMOopClosure*             _cm_oop_closure;

   685 

   686   // the region this task is scanning, NULL if we're not scanning any

   687   HeapRegion*                 _curr_region;

   688   // the local finger of this task, NULL if we're not scanning a region

   689   HeapWord*                   _finger;

   690   // limit of the region this task is scanning, NULL if we're not scanning one

   691   HeapWord*                   _region_limit;

   692 

   693   // the number of words this task has scanned

   694   size_t                      _words_scanned;

   695   // When _words_scanned reaches this limit, the regular clock is

   696   // called. Notice that this might be decreased under certain

   697   // circumstances (i.e. when we believe that we did an expensive

   698   // operation).

   699   size_t                      _words_scanned_limit;

   700   // the initial value of _words_scanned_limit (i.e. what it was

   701   // before it was decreased).

   702   size_t                      _real_words_scanned_limit;

   703 

   704   // the number of references this task has visited

   705   size_t                      _refs_reached;

   706   // When _refs_reached reaches this limit, the regular clock is

   707   // called. Notice this this might be decreased under certain

   708   // circumstances (i.e. when we believe that we did an expensive

   709   // operation).

   710   size_t                      _refs_reached_limit;

   711   // the initial value of _refs_reached_limit (i.e. what it was before

   712   // it was decreased).

   713   size_t                      _real_refs_reached_limit;

   714 

   715   // used by the work stealing stuff

   716   int                         _hash_seed;

   717   // if this is true, then the task has aborted for some reason

   718   bool                        _has_aborted;

   719   // set when the task aborts because it has met its time quota

   720   bool                        _has_timed_out;

   721   // true when we're draining SATB buffers; this avoids the task

   722   // aborting due to SATB buffers being available (as we're already

   723   // dealing with them)

   724   bool                        _draining_satb_buffers;

   725 

   726   // number sequence of past step times

   727   NumberSeq                   _step_times_ms;

   728   // elapsed time of this task

   729   double                      _elapsed_time_ms;

   730   // termination time of this task

   731   double                      _termination_time_ms;

   732   // when this task got into the termination protocol

   733   double                      _termination_start_time_ms;

   734 

   735   // true when the task is during a concurrent phase, false when it is

   736   // in the remark phase (so, in the latter case, we do not have to

   737   // check all the things that we have to check during the concurrent

   738   // phase, i.e. SATB buffer availability...)

   739   bool                        _concurrent;

   740 

   741   TruncatedSeq                _marking_step_diffs_ms;

   742 

   743   // it updates the local fields after this task has claimed

   744   // a new region to scan

   745   void setup_for_region(HeapRegion* hr);

   746   // it brings up-to-date the limit of the region

   747   void update_region_limit();

   748 

   749   // called when either the words scanned or the refs visited limit

   750   // has been reached

   751   void reached_limit();

   752   // recalculates the words scanned and refs visited limits

   753   void recalculate_limits();

   754   // decreases the words scanned and refs visited limits when we reach

   755   // an expensive operation

   756   void decrease_limits();

   757   // it checks whether the words scanned or refs visited reached their

   758   // respective limit and calls reached_limit() if they have

   759   void check_limits() {

   760     if (_words_scanned >= _words_scanned_limit ||

   761         _refs_reached >= _refs_reached_limit) {

   762       reached_limit();

   763     }

   764   }

   765   // this is supposed to be called regularly during a marking step as

   766   // it checks a bunch of conditions that might cause the marking step

   767   // to abort

   768   void regular_clock_call();

   769   bool concurrent() { return _concurrent; }

   770 

   771   // Test whether obj might have already been passed over by the

   772   // mark bitmap scan, and so needs to be pushed onto the mark stack.

   773   bool is_below_finger(oop obj, HeapWord* global_finger) const;

   774 

   775   template<bool scan> void process_grey_task_entry(G1TaskQueueEntry task_entry);

   776 public:

   777   // Apply the closure on the given area of the objArray. Return the number of words

   778   // scanned.

   779   inline size_t scan_objArray(objArrayOop obj, MemRegion mr);

   780   // It resets the task; it should be called right at the beginning of

   781   // a marking phase.

   782   void reset(G1CMBitMap* _nextMarkBitMap);

   783   // it clears all the fields that correspond to a claimed region.

   784   void clear_region_fields();

   785 

   786   void set_concurrent(bool concurrent) { _concurrent = concurrent; }

   787 

   788   // The main method of this class which performs a marking step

   789   // trying not to exceed the given duration. However, it might exit

   790   // prematurely, according to some conditions (i.e. SATB buffers are

   791   // available for processing).

   792   void do_marking_step(double target_ms,

   793                        bool do_termination,

   794                        bool is_serial);

   795 

   796   // These two calls start and stop the timer

   797   void record_start_time() {

   798     _elapsed_time_ms = os::elapsedTime() * 1000.0;

   799   }

   800   void record_end_time() {

   801     _elapsed_time_ms = os::elapsedTime() * 1000.0 - _elapsed_time_ms;

   802   }

   803 

   804   // returns the worker ID associated with this task.

   805   uint worker_id() { return _worker_id; }

   806 

   807   // From TerminatorTerminator. It determines whether this task should

   808   // exit the termination protocol after it's entered it.

   809   virtual bool should_exit_termination();

   810 

   811   // Resets the local region fields after a task has finished scanning a

   812   // region; or when they have become stale as a result of the region

   813   // being evacuated.

   814   void giveup_current_region();

   815 

   816   HeapWord* finger()            { return _finger; }

   817 

   818   bool has_aborted()            { return _has_aborted; }

   819   void set_has_aborted()        { _has_aborted = true; }

   820   void clear_has_aborted()      { _has_aborted = false; }

   821   bool has_timed_out()          { return _has_timed_out; }

   822   bool claimed()                { return _claimed; }

   823 

   824   void set_cm_oop_closure(G1CMOopClosure* cm_oop_closure);

   825 

   826   // Increment the number of references this task has visited.

   827   void increment_refs_reached() { ++_refs_reached; }

   828 

   829   // Grey the object by marking it.  If not already marked, push it on

   830   // the local queue if below the finger.

   831   // obj is below its region's NTAMS.

   832   inline void make_reference_grey(oop obj);

   833 

   834   // Grey the object (by calling make_grey_reference) if required,

   835   // e.g. obj is below its containing region's NTAMS.

   836   // Precondition: obj is a valid heap object.

   837   inline void deal_with_reference(oop obj);

   838 

   839   // It scans an object and visits its children.

   840   inline void scan_task_entry(G1TaskQueueEntry task_entry);

   841 

   842   // It pushes an object on the local queue.

   843   inline void push(G1TaskQueueEntry task_entry);

   844 

   845   // Move entries to the global stack.

   846   void move_entries_to_global_stack();

   847   // Move entries from the global stack, return true if we were successful to do so.

   848   bool get_entries_from_global_stack();

   849 

   850   // It pops and scans objects from the local queue. If partially is

   851   // true, then it stops when the queue size is of a given limit. If

   852   // partially is false, then it stops when the queue is empty.

   853   void drain_local_queue(bool partially);

   854   // It moves entries from the global stack to the local queue and

   855   // drains the local queue. If partially is true, then it stops when

   856   // both the global stack and the local queue reach a given size. If

   857   // partially if false, it tries to empty them totally.

   858   void drain_global_stack(bool partially);

   859   // It keeps picking SATB buffers and processing them until no SATB

   860   // buffers are available.

   861   void drain_satb_buffers();

   862 

   863   // moves the local finger to a new location

   864   inline void move_finger_to(HeapWord* new_finger) {

   865     assert(new_finger >= _finger && new_finger < _region_limit, "invariant");

   866     _finger = new_finger;

   867   }

   868 

   869   G1CMTask(uint worker_id,

   870            G1ConcurrentMark *cm,

   871            G1CMTaskQueue* task_queue,

   872            G1CMTaskQueueSet* task_queues);

   873 

   874   // it prints statistics associated with this task

   875   void print_stats();

   876 };

   877 

   878 // Class that's used to to print out per-region liveness

   879 // information. It's currently used at the end of marking and also

   880 // after we sort the old regions at the end of the cleanup operation.

   881 class G1PrintRegionLivenessInfoClosure: public HeapRegionClosure {

   882 private:

   883   // Accumulators for these values.

   884   size_t _total_used_bytes;

   885   size_t _total_capacity_bytes;

   886   size_t _total_prev_live_bytes;

   887   size_t _total_next_live_bytes;

   888 

   889   // Accumulator for the remembered set size

   890   size_t _total_remset_bytes;

   891 

   892   // Accumulator for strong code roots memory size

   893   size_t _total_strong_code_roots_bytes;

   894 

   895   static double perc(size_t val, size_t total) {

   896     if (total == 0) {

   897       return 0.0;

   898     } else {

   899       return 100.0 * ((double) val / (double) total);

   900     }

   901   }

   902 

   903   static double bytes_to_mb(size_t val) {

   904     return (double) val / (double) M;

   905   }

   906 

   907 public:

   908   // The header and footer are printed in the constructor and

   909   // destructor respectively.

   910   G1PrintRegionLivenessInfoClosure(const char* phase_name);

   911   virtual bool doHeapRegion(HeapRegion* r);

   912   ~G1PrintRegionLivenessInfoClosure();

   913 };

   914 

   915 #endif // SHARE_VM_GC_G1_G1CONCURRENTMARK_HPP