6711316: Open source the Garbage-First garbage collector
Summary: First mercurial integration of the code for the Garbage-First garbage collector.
Reviewed-by: apetrusenko, iveresov, jmasa, sgoldman, tonyp, ysr
/*
* Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
* have any questions.
*
*/
class G1CollectedHeap;
class CMTask;
typedef GenericTaskQueue<oop> CMTaskQueue;
typedef GenericTaskQueueSet<oop> CMTaskQueueSet;
// A generic CM bit map. This is essentially a wrapper around the BitMap
// class, with one bit per (1<<_shifter) HeapWords.
class CMBitMapRO {
protected:
HeapWord* _bmStartWord; // base address of range covered by map
size_t _bmWordSize; // map size (in #HeapWords covered)
const int _shifter; // map to char or bit
VirtualSpace _virtual_space; // underlying the bit map
BitMap _bm; // the bit map itself
public:
// constructor
CMBitMapRO(ReservedSpace rs, int shifter);
enum { do_yield = true };
// inquiries
HeapWord* startWord() const { return _bmStartWord; }
size_t sizeInWords() const { return _bmWordSize; }
// the following is one past the last word in space
HeapWord* endWord() const { return _bmStartWord + _bmWordSize; }
// read marks
bool isMarked(HeapWord* addr) const {
assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
"outside underlying space?");
return _bm.at(heapWordToOffset(addr));
}
// iteration
bool iterate(BitMapClosure* cl) { return _bm.iterate(cl); }
bool iterate(BitMapClosure* cl, MemRegion mr);
// Return the address corresponding to the next marked bit at or after
// "addr", and before "limit", if "limit" is non-NULL. If there is no
// such bit, returns "limit" if that is non-NULL, or else "endWord()".
HeapWord* getNextMarkedWordAddress(HeapWord* addr,
HeapWord* limit = NULL) const;
// Return the address corresponding to the next unmarked bit at or after
// "addr", and before "limit", if "limit" is non-NULL. If there is no
// such bit, returns "limit" if that is non-NULL, or else "endWord()".
HeapWord* getNextUnmarkedWordAddress(HeapWord* addr,
HeapWord* limit = NULL) const;
// conversion utilities
// XXX Fix these so that offsets are size_t's...
HeapWord* offsetToHeapWord(size_t offset) const {
return _bmStartWord + (offset << _shifter);
}
size_t heapWordToOffset(HeapWord* addr) const {
return pointer_delta(addr, _bmStartWord) >> _shifter;
}
int heapWordDiffToOffsetDiff(size_t diff) const;
HeapWord* nextWord(HeapWord* addr) {
return offsetToHeapWord(heapWordToOffset(addr) + 1);
}
void mostly_disjoint_range_union(BitMap* from_bitmap,
size_t from_start_index,
HeapWord* to_start_word,
size_t word_num);
// debugging
NOT_PRODUCT(bool covers(ReservedSpace rs) const;)
};
class CMBitMap : public CMBitMapRO {
public:
// constructor
CMBitMap(ReservedSpace rs, int shifter) :
CMBitMapRO(rs, shifter) {}
// write marks
void mark(HeapWord* addr) {
assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
"outside underlying space?");
_bm.at_put(heapWordToOffset(addr), true);
}
void clear(HeapWord* addr) {
assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
"outside underlying space?");
_bm.at_put(heapWordToOffset(addr), false);
}
bool parMark(HeapWord* addr) {
assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
"outside underlying space?");
return _bm.par_at_put(heapWordToOffset(addr), true);
}
bool parClear(HeapWord* addr) {
assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
"outside underlying space?");
return _bm.par_at_put(heapWordToOffset(addr), false);
}
void markRange(MemRegion mr);
void clearAll();
void clearRange(MemRegion mr);
// Starting at the bit corresponding to "addr" (inclusive), find the next
// "1" bit, if any. This bit starts some run of consecutive "1"'s; find
// the end of this run (stopping at "end_addr"). Return the MemRegion
// covering from the start of the region corresponding to the first bit
// of the run to the end of the region corresponding to the last bit of
// the run. If there is no "1" bit at or after "addr", return an empty
// MemRegion.
MemRegion getAndClearMarkedRegion(HeapWord* addr, HeapWord* end_addr);
};
// Represents a marking stack used by the CM collector.
// Ideally this should be GrowableArray<> just like MSC's marking stack(s).
class CMMarkStack {
ConcurrentMark* _cm;
oop* _base; // bottom of stack
jint _index; // one more than last occupied index
jint _capacity; // max #elements
jint _oops_do_bound; // Number of elements to include in next iteration.
NOT_PRODUCT(jint _max_depth;) // max depth plumbed during run
bool _overflow;
DEBUG_ONLY(bool _drain_in_progress;)
DEBUG_ONLY(bool _drain_in_progress_yields;)
public:
CMMarkStack(ConcurrentMark* cm);
~CMMarkStack();
void allocate(size_t size);
oop pop() {
if (!isEmpty()) {
return _base[--_index] ;
}
return NULL;
}
// If overflow happens, don't do the push, and record the overflow.
// *Requires* that "ptr" is already marked.
void push(oop ptr) {
if (isFull()) {
// Record overflow.
_overflow = true;
return;
} else {
_base[_index++] = ptr;
NOT_PRODUCT(_max_depth = MAX2(_max_depth, _index));
}
}
// Non-block impl. Note: concurrency is allowed only with other
// "par_push" operations, not with "pop" or "drain". We would need
// parallel versions of them if such concurrency was desired.
void par_push(oop ptr);
// Pushes the first "n" elements of "ptr_arr" on the stack.
// Non-block impl. Note: concurrency is allowed only with other
// "par_adjoin_arr" or "push" operations, not with "pop" or "drain".
void par_adjoin_arr(oop* ptr_arr, int n);
// Pushes the first "n" elements of "ptr_arr" on the stack.
// Locking impl: concurrency is allowed only with
// "par_push_arr" and/or "par_pop_arr" operations, which use the same
// locking strategy.
void par_push_arr(oop* ptr_arr, int n);
// If returns false, the array was empty. Otherwise, removes up to "max"
// elements from the stack, and transfers them to "ptr_arr" in an
// unspecified order. The actual number transferred is given in "n" ("n
// == 0" is deliberately redundant with the return value.) Locking impl:
// concurrency is allowed only with "par_push_arr" and/or "par_pop_arr"
// operations, which use the same locking strategy.
bool par_pop_arr(oop* ptr_arr, int max, int* n);
// Drain the mark stack, applying the given closure to all fields of
// objects on the stack. (That is, continue until the stack is empty,
// even if closure applications add entries to the stack.) The "bm"
// argument, if non-null, may be used to verify that only marked objects
// are on the mark stack. If "yield_after" is "true", then the
// concurrent marker performing the drain offers to yield after
// processing each object. If a yield occurs, stops the drain operation
// and returns false. Otherwise, returns true.
template<class OopClosureClass>
bool drain(OopClosureClass* cl, CMBitMap* bm, bool yield_after = false);
bool isEmpty() { return _index == 0; }
bool isFull() { return _index == _capacity; }
int maxElems() { return _capacity; }
bool overflow() { return _overflow; }
void clear_overflow() { _overflow = false; }
int size() { return _index; }
void setEmpty() { _index = 0; clear_overflow(); }
// Record the current size; a subsequent "oops_do" will iterate only over
// indices valid at the time of this call.
void set_oops_do_bound(jint bound = -1) {
if (bound == -1) {
_oops_do_bound = _index;
} else {
_oops_do_bound = bound;
}
}
jint oops_do_bound() { return _oops_do_bound; }
// iterate over the oops in the mark stack, up to the bound recorded via
// the call above.
void oops_do(OopClosure* f);
};
class CMRegionStack {
MemRegion* _base;
jint _capacity;
jint _index;
jint _oops_do_bound;
bool _overflow;
public:
CMRegionStack();
~CMRegionStack();
void allocate(size_t size);
// This is lock-free; assumes that it will only be called in parallel
// with other "push" operations (no pops).
void push(MemRegion mr);
// Lock-free; assumes that it will only be called in parallel
// with other "pop" operations (no pushes).
MemRegion pop();
bool isEmpty() { return _index == 0; }
bool isFull() { return _index == _capacity; }
bool overflow() { return _overflow; }
void clear_overflow() { _overflow = false; }
int size() { return _index; }
// It iterates over the entries in the region stack and it
// invalidates (i.e. assigns MemRegion()) the ones that point to
// regions in the collection set.
bool invalidate_entries_into_cset();
// This gives an upper bound up to which the iteration in
// invalidate_entries_into_cset() will reach. This prevents
// newly-added entries to be unnecessarily scanned.
void set_oops_do_bound() {
_oops_do_bound = _index;
}
void setEmpty() { _index = 0; clear_overflow(); }
};
// this will enable a variety of different statistics per GC task
#define _MARKING_STATS_ 0
// this will enable the higher verbose levels
#define _MARKING_VERBOSE_ 0
#if _MARKING_STATS_
#define statsOnly(statement) \
do { \
statement ; \
} while (0)
#else // _MARKING_STATS_
#define statsOnly(statement) \
do { \
} while (0)
#endif // _MARKING_STATS_
// Some extra guarantees that I like to also enable in optimised mode
// when debugging. If you want to enable them, comment out the assert
// macro and uncomment out the guaratee macro
// #define tmp_guarantee_CM(expr, str) guarantee(expr, str)
#define tmp_guarantee_CM(expr, str) assert(expr, str)
typedef enum {
no_verbose = 0, // verbose turned off
stats_verbose, // only prints stats at the end of marking
low_verbose, // low verbose, mostly per region and per major event
medium_verbose, // a bit more detailed than low
high_verbose // per object verbose
} CMVerboseLevel;
class ConcurrentMarkThread;
class ConcurrentMark {
friend class ConcurrentMarkThread;
friend class CMTask;
friend class CMBitMapClosure;
friend class CSMarkOopClosure;
friend class CMGlobalObjectClosure;
friend class CMRemarkTask;
friend class CMConcurrentMarkingTask;
friend class G1ParNoteEndTask;
friend class CalcLiveObjectsClosure;
protected:
ConcurrentMarkThread* _cmThread; // the thread doing the work
G1CollectedHeap* _g1h; // the heap.
size_t _parallel_marking_threads; // the number of marking
// threads we'll use
double _sleep_factor; // how much we have to sleep, with
// respect to the work we just did, to
// meet the marking overhead goal
double _marking_task_overhead; // marking target overhead for
// a single task
// same as the two above, but for the cleanup task
double _cleanup_sleep_factor;
double _cleanup_task_overhead;
// Stuff related to age cohort processing.
struct ParCleanupThreadState {
char _pre[64];
UncleanRegionList list;
char _post[64];
};
ParCleanupThreadState** _par_cleanup_thread_state;
// CMS marking support structures
CMBitMap _markBitMap1;
CMBitMap _markBitMap2;
CMBitMapRO* _prevMarkBitMap; // completed mark bitmap
CMBitMap* _nextMarkBitMap; // under-construction mark bitmap
bool _at_least_one_mark_complete;
BitMap _region_bm;
BitMap _card_bm;
// Heap bounds
HeapWord* _heap_start;
HeapWord* _heap_end;
// For gray objects
CMMarkStack _markStack; // Grey objects behind global finger.
CMRegionStack _regionStack; // Grey regions behind global finger.
HeapWord* volatile _finger; // the global finger, region aligned,
// always points to the end of the
// last claimed region
// marking tasks
size_t _max_task_num; // maximum task number
size_t _active_tasks; // task num currently active
CMTask** _tasks; // task queue array (max_task_num len)
CMTaskQueueSet* _task_queues; // task queue set
ParallelTaskTerminator _terminator; // for termination
// Two sync barriers that are used to synchronise tasks when an
// overflow occurs. The algorithm is the following. All tasks enter
// the first one to ensure that they have all stopped manipulating
// the global data structures. After they exit it, they re-initialise
// their data structures and task 0 re-initialises the global data
// structures. Then, they enter the second sync barrier. This
// ensure, that no task starts doing work before all data
// structures (local and global) have been re-initialised. When they
// exit it, they are free to start working again.
WorkGangBarrierSync _first_overflow_barrier_sync;
WorkGangBarrierSync _second_overflow_barrier_sync;
// this is set by any task, when an overflow on the global data
// structures is detected.
volatile bool _has_overflown;
// true: marking is concurrent, false: we're in remark
volatile bool _concurrent;
// set at the end of a Full GC so that marking aborts
volatile bool _has_aborted;
// used when remark aborts due to an overflow to indicate that
// another concurrent marking phase should start
volatile bool _restart_for_overflow;
// This is true from the very start of concurrent marking until the
// point when all the tasks complete their work. It is really used
// to determine the points between the end of concurrent marking and
// time of remark.
volatile bool _concurrent_marking_in_progress;
// verbose level
CMVerboseLevel _verbose_level;
COTracker _cleanup_co_tracker;
// These two fields are used to implement the optimisation that
// avoids pushing objects on the global/region stack if there are
// no collection set regions above the lowest finger.
// This is the lowest finger (among the global and local fingers),
// which is calculated before a new collection set is chosen.
HeapWord* _min_finger;
// If this flag is true, objects/regions that are marked below the
// finger should be pushed on the stack(s). If this is flag is
// false, it is safe not to push them on the stack(s).
bool _should_gray_objects;
// All of these times are in ms.
NumberSeq _init_times;
NumberSeq _remark_times;
NumberSeq _remark_mark_times;
NumberSeq _remark_weak_ref_times;
NumberSeq _cleanup_times;
double _total_counting_time;
double _total_rs_scrub_time;
double* _accum_task_vtime; // accumulated task vtime
WorkGang* _parallel_workers;
void weakRefsWork(bool clear_all_soft_refs);
void swapMarkBitMaps();
// It resets the global marking data structures, as well as the
// task local ones; should be called during initial mark.
void reset();
// It resets all the marking data structures.
void clear_marking_state();
// It should be called to indicate which phase we're in (concurrent
// mark or remark) and how many threads are currently active.
void set_phase(size_t active_tasks, bool concurrent);
// We do this after we're done with marking so that the marking data
// structures are initialised to a sensible and predictable state.
void set_non_marking_state();
// prints all gathered CM-related statistics
void print_stats();
// accessor methods
size_t parallel_marking_threads() { return _parallel_marking_threads; }
double sleep_factor() { return _sleep_factor; }
double marking_task_overhead() { return _marking_task_overhead;}
double cleanup_sleep_factor() { return _cleanup_sleep_factor; }
double cleanup_task_overhead() { return _cleanup_task_overhead;}
HeapWord* finger() { return _finger; }
bool concurrent() { return _concurrent; }
size_t active_tasks() { return _active_tasks; }
ParallelTaskTerminator* terminator() { return &_terminator; }
// It claims the next available region to be scanned by a marking
// task. It might return NULL if the next region is empty or we have
// run out of regions. In the latter case, out_of_regions()
// determines whether we've really run out of regions or the task
// should call claim_region() again. This might seem a bit
// awkward. Originally, the code was written so that claim_region()
// either successfully returned with a non-empty region or there
// were no more regions to be claimed. The problem with this was
// that, in certain circumstances, it iterated over large chunks of
// the heap finding only empty regions and, while it was working, it
// was preventing the calling task to call its regular clock
// method. So, this way, each task will spend very little time in
// claim_region() and is allowed to call the regular clock method
// frequently.
HeapRegion* claim_region(int task);
// It determines whether we've run out of regions to scan.
bool out_of_regions() { return _finger == _heap_end; }
// Returns the task with the given id
CMTask* task(int id) {
guarantee( 0 <= id && id < (int) _active_tasks, "task id not within "
"active bounds" );
return _tasks[id];
}
// Returns the task queue with the given id
CMTaskQueue* task_queue(int id) {
guarantee( 0 <= id && id < (int) _active_tasks, "task queue id not within "
"active bounds" );
return (CMTaskQueue*) _task_queues->queue(id);
}
// Returns the task queue set
CMTaskQueueSet* task_queues() { return _task_queues; }
// Access / manipulation of the overflow flag which is set to
// indicate that the global stack or region stack has overflown
bool has_overflown() { return _has_overflown; }
void set_has_overflown() { _has_overflown = true; }
void clear_has_overflown() { _has_overflown = false; }
bool has_aborted() { return _has_aborted; }
bool restart_for_overflow() { return _restart_for_overflow; }
// Methods to enter the two overflow sync barriers
void enter_first_sync_barrier(int task_num);
void enter_second_sync_barrier(int task_num);
public:
// Manipulation of the global mark stack.
// Notice that the first mark_stack_push is CAS-based, whereas the
// two below are Mutex-based. This is OK since the first one is only
// called during evacuation pauses and doesn't compete with the
// other two (which are called by the marking tasks during
// concurrent marking or remark).
bool mark_stack_push(oop p) {
_markStack.par_push(p);
if (_markStack.overflow()) {
set_has_overflown();
return false;
}
return true;
}
bool mark_stack_push(oop* arr, int n) {
_markStack.par_push_arr(arr, n);
if (_markStack.overflow()) {
set_has_overflown();
return false;
}
return true;
}
void mark_stack_pop(oop* arr, int max, int* n) {
_markStack.par_pop_arr(arr, max, n);
}
size_t mark_stack_size() { return _markStack.size(); }
size_t partial_mark_stack_size_target() { return _markStack.maxElems()/3; }
bool mark_stack_overflow() { return _markStack.overflow(); }
bool mark_stack_empty() { return _markStack.isEmpty(); }
// Manipulation of the region stack
bool region_stack_push(MemRegion mr) {
_regionStack.push(mr);
if (_regionStack.overflow()) {
set_has_overflown();
return false;
}
return true;
}
MemRegion region_stack_pop() { return _regionStack.pop(); }
int region_stack_size() { return _regionStack.size(); }
bool region_stack_overflow() { return _regionStack.overflow(); }
bool region_stack_empty() { return _regionStack.isEmpty(); }
bool concurrent_marking_in_progress() {
return _concurrent_marking_in_progress;
}
void set_concurrent_marking_in_progress() {
_concurrent_marking_in_progress = true;
}
void clear_concurrent_marking_in_progress() {
_concurrent_marking_in_progress = false;
}
void update_accum_task_vtime(int i, double vtime) {
_accum_task_vtime[i] += vtime;
}
double all_task_accum_vtime() {
double ret = 0.0;
for (int i = 0; i < (int)_max_task_num; ++i)
ret += _accum_task_vtime[i];
return ret;
}
// Attempts to steal an object from the task queues of other tasks
bool try_stealing(int task_num, int* hash_seed, oop& obj) {
return _task_queues->steal(task_num, hash_seed, obj);
}
// It grays an object by first marking it. Then, if it's behind the
// global finger, it also pushes it on the global stack.
void deal_with_reference(oop obj);
ConcurrentMark(ReservedSpace rs, int max_regions);
~ConcurrentMark();
ConcurrentMarkThread* cmThread() { return _cmThread; }
CMBitMapRO* prevMarkBitMap() const { return _prevMarkBitMap; }
CMBitMap* nextMarkBitMap() const { return _nextMarkBitMap; }
// The following three are interaction between CM and
// G1CollectedHeap
// This notifies CM that a root during initial-mark needs to be
// grayed and it's MT-safe. Currently, we just mark it. But, in the
// future, we can experiment with pushing it on the stack and we can
// do this without changing G1CollectedHeap.
void grayRoot(oop p);
// It's used during evacuation pauses to gray a region, if
// necessary, and it's MT-safe. It assumes that the caller has
// marked any objects on that region. If _should_gray_objects is
// true and we're still doing concurrent marking, the region is
// pushed on the region stack, if it is located below the global
// finger, otherwise we do nothing.
void grayRegionIfNecessary(MemRegion mr);
// It's used during evacuation pauses to mark and, if necessary,
// gray a single object and it's MT-safe. It assumes the caller did
// not mark the object. If _should_gray_objects is true and we're
// still doing concurrent marking, the objects is pushed on the
// global stack, if it is located below the global finger, otherwise
// we do nothing.
void markAndGrayObjectIfNecessary(oop p);
// This iterates over the bitmap of the previous marking and prints
// out all objects that are marked on the bitmap and indicates
// whether what they point to is also marked or not.
void print_prev_bitmap_reachable();
// Clear the next marking bitmap (will be called concurrently).
void clearNextBitmap();
// main CMS steps and related support
void checkpointRootsInitial();
// These two do the work that needs to be done before and after the
// initial root checkpoint. Since this checkpoint can be done at two
// different points (i.e. an explicit pause or piggy-backed on a
// young collection), then it's nice to be able to easily share the
// pre/post code. It might be the case that we can put everything in
// the post method. TP
void checkpointRootsInitialPre();
void checkpointRootsInitialPost();
// Do concurrent phase of marking, to a tentative transitive closure.
void markFromRoots();
// Process all unprocessed SATB buffers. It is called at the
// beginning of an evacuation pause.
void drainAllSATBBuffers();
void checkpointRootsFinal(bool clear_all_soft_refs);
void checkpointRootsFinalWork();
void calcDesiredRegions();
void cleanup();
void completeCleanup();
// Mark in the previous bitmap. NB: this is usually read-only, so use
// this carefully!
void markPrev(oop p);
void clear(oop p);
// Clears marks for all objects in the given range, for both prev and
// next bitmaps. NB: the previous bitmap is usually read-only, so use
// this carefully!
void clearRangeBothMaps(MemRegion mr);
// Record the current top of the mark and region stacks; a
// subsequent oops_do() on the mark stack and
// invalidate_entries_into_cset() on the region stack will iterate
// only over indices valid at the time of this call.
void set_oops_do_bound() {
_markStack.set_oops_do_bound();
_regionStack.set_oops_do_bound();
}
// Iterate over the oops in the mark stack and all local queues. It
// also calls invalidate_entries_into_cset() on the region stack.
void oops_do(OopClosure* f);
// It is called at the end of an evacuation pause during marking so
// that CM is notified of where the new end of the heap is. It
// doesn't do anything if concurrent_marking_in_progress() is false,
// unless the force parameter is true.
void update_g1_committed(bool force = false);
void complete_marking_in_collection_set();
// It indicates that a new collection set is being chosen.
void newCSet();
// It registers a collection set heap region with CM. This is used
// to determine whether any heap regions are located above the finger.
void registerCSetRegion(HeapRegion* hr);
// Returns "true" if at least one mark has been completed.
bool at_least_one_mark_complete() { return _at_least_one_mark_complete; }
bool isMarked(oop p) const {
assert(p != NULL && p->is_oop(), "expected an oop");
HeapWord* addr = (HeapWord*)p;
assert(addr >= _nextMarkBitMap->startWord() ||
addr < _nextMarkBitMap->endWord(), "in a region");
return _nextMarkBitMap->isMarked(addr);
}
inline bool not_yet_marked(oop p) const;
// XXX Debug code
bool containing_card_is_marked(void* p);
bool containing_cards_are_marked(void* start, void* last);
bool isPrevMarked(oop p) const {
assert(p != NULL && p->is_oop(), "expected an oop");
HeapWord* addr = (HeapWord*)p;
assert(addr >= _prevMarkBitMap->startWord() ||
addr < _prevMarkBitMap->endWord(), "in a region");
return _prevMarkBitMap->isMarked(addr);
}
inline bool do_yield_check(int worker_i = 0);
inline bool should_yield();
// Called to abort the marking cycle after a Full GC takes palce.
void abort();
void disable_co_trackers();
// This prints the global/local fingers. It is used for debugging.
NOT_PRODUCT(void print_finger();)
void print_summary_info();
// The following indicate whether a given verbose level has been
// set. Notice that anything above stats is conditional to
// _MARKING_VERBOSE_ having been set to 1
bool verbose_stats()
{ return _verbose_level >= stats_verbose; }
bool verbose_low()
{ return _MARKING_VERBOSE_ && _verbose_level >= low_verbose; }
bool verbose_medium()
{ return _MARKING_VERBOSE_ && _verbose_level >= medium_verbose; }
bool verbose_high()
{ return _MARKING_VERBOSE_ && _verbose_level >= high_verbose; }
};
// A class representing a marking task.
class CMTask : public TerminatorTerminator {
private:
enum PrivateConstants {
// the regular clock call is called once the scanned words reaches
// this limit
words_scanned_period = 12*1024,
// the regular clock call is called once the number of visited
// references reaches this limit
refs_reached_period = 384,
// initial value for the hash seed, used in the work stealing code
init_hash_seed = 17,
// how many entries will be transferred between global stack and
// local queues
global_stack_transfer_size = 16
};
int _task_id;
G1CollectedHeap* _g1h;
ConcurrentMark* _cm;
CMBitMap* _nextMarkBitMap;
// the task queue of this task
CMTaskQueue* _task_queue;
// the task queue set---needed for stealing
CMTaskQueueSet* _task_queues;
// indicates whether the task has been claimed---this is only for
// debugging purposes
bool _claimed;
// number of calls to this task
int _calls;
// concurrent overhead over a single CPU for this task
COTracker _co_tracker;
// when the virtual timer reaches this time, the marking step should
// exit
double _time_target_ms;
// the start time of the current marking step
double _start_time_ms;
// the oop closure used for iterations over oops
OopClosure* _oop_closure;
// the region this task is scanning, NULL if we're not scanning any
HeapRegion* _curr_region;
// the local finger of this task, NULL if we're not scanning a region
HeapWord* _finger;
// limit of the region this task is scanning, NULL if we're not scanning one
HeapWord* _region_limit;
// This is used only when we scan regions popped from the region
// stack. It records what the last object on such a region we
// scanned was. It is used to ensure that, if we abort region
// iteration, we do not rescan the first part of the region. This
// should be NULL when we're not scanning a region from the region
// stack.
HeapWord* _region_finger;
// the number of words this task has scanned
size_t _words_scanned;
// When _words_scanned reaches this limit, the regular clock is
// called. Notice that this might be decreased under certain
// circumstances (i.e. when we believe that we did an expensive
// operation).
size_t _words_scanned_limit;
// the initial value of _words_scanned_limit (i.e. what it was
// before it was decreased).
size_t _real_words_scanned_limit;
// the number of references this task has visited
size_t _refs_reached;
// When _refs_reached reaches this limit, the regular clock is
// called. Notice this this might be decreased under certain
// circumstances (i.e. when we believe that we did an expensive
// operation).
size_t _refs_reached_limit;
// the initial value of _refs_reached_limit (i.e. what it was before
// it was decreased).
size_t _real_refs_reached_limit;
// used by the work stealing stuff
int _hash_seed;
// if this is true, then the task has aborted for some reason
bool _has_aborted;
// set when the task aborts because it has met its time quota
bool _has_aborted_timed_out;
// true when we're draining SATB buffers; this avoids the task
// aborting due to SATB buffers being available (as we're already
// dealing with them)
bool _draining_satb_buffers;
// number sequence of past step times
NumberSeq _step_times_ms;
// elapsed time of this task
double _elapsed_time_ms;
// termination time of this task
double _termination_time_ms;
// when this task got into the termination protocol
double _termination_start_time_ms;
// true when the task is during a concurrent phase, false when it is
// in the remark phase (so, in the latter case, we do not have to
// check all the things that we have to check during the concurrent
// phase, i.e. SATB buffer availability...)
bool _concurrent;
TruncatedSeq _marking_step_diffs_ms;
// LOTS of statistics related with this task
#if _MARKING_STATS_
NumberSeq _all_clock_intervals_ms;
double _interval_start_time_ms;
int _aborted;
int _aborted_overflow;
int _aborted_cm_aborted;
int _aborted_yield;
int _aborted_timed_out;
int _aborted_satb;
int _aborted_termination;
int _steal_attempts;
int _steals;
int _clock_due_to_marking;
int _clock_due_to_scanning;
int _local_pushes;
int _local_pops;
int _local_max_size;
int _objs_scanned;
int _global_pushes;
int _global_pops;
int _global_max_size;
int _global_transfers_to;
int _global_transfers_from;
int _region_stack_pops;
int _regions_claimed;
int _objs_found_on_bitmap;
int _satb_buffers_processed;
#endif // _MARKING_STATS_
// it updates the local fields after this task has claimed
// a new region to scan
void setup_for_region(HeapRegion* hr);
// it brings up-to-date the limit of the region
void update_region_limit();
// it resets the local fields after a task has finished scanning a
// region
void giveup_current_region();
// called when either the words scanned or the refs visited limit
// has been reached
void reached_limit();
// recalculates the words scanned and refs visited limits
void recalculate_limits();
// decreases the words scanned and refs visited limits when we reach
// an expensive operation
void decrease_limits();
// it checks whether the words scanned or refs visited reached their
// respective limit and calls reached_limit() if they have
void check_limits() {
if (_words_scanned >= _words_scanned_limit ||
_refs_reached >= _refs_reached_limit)
reached_limit();
}
// this is supposed to be called regularly during a marking step as
// it checks a bunch of conditions that might cause the marking step
// to abort
void regular_clock_call();
bool concurrent() { return _concurrent; }
public:
// It resets the task; it should be called right at the beginning of
// a marking phase.
void reset(CMBitMap* _nextMarkBitMap);
// it clears all the fields that correspond to a claimed region.
void clear_region_fields();
void set_concurrent(bool concurrent) { _concurrent = concurrent; }
void enable_co_tracker() {
guarantee( !_co_tracker.enabled(), "invariant" );
_co_tracker.enable();
}
void disable_co_tracker() {
guarantee( _co_tracker.enabled(), "invariant" );
_co_tracker.disable();
}
bool co_tracker_enabled() {
return _co_tracker.enabled();
}
void reset_co_tracker(double starting_conc_overhead = 0.0) {
_co_tracker.reset(starting_conc_overhead);
}
void start_co_tracker() {
_co_tracker.start();
}
void update_co_tracker(bool force_end = false) {
_co_tracker.update(force_end);
}
// The main method of this class which performs a marking step
// trying not to exceed the given duration. However, it might exit
// prematurely, according to some conditions (i.e. SATB buffers are
// available for processing).
void do_marking_step(double target_ms);
// These two calls start and stop the timer
void record_start_time() {
_elapsed_time_ms = os::elapsedTime() * 1000.0;
}
void record_end_time() {
_elapsed_time_ms = os::elapsedTime() * 1000.0 - _elapsed_time_ms;
}
// returns the task ID
int task_id() { return _task_id; }
// From TerminatorTerminator. It determines whether this task should
// exit the termination protocol after it's entered it.
virtual bool should_exit_termination();
HeapWord* finger() { return _finger; }
bool has_aborted() { return _has_aborted; }
void set_has_aborted() { _has_aborted = true; }
void clear_has_aborted() { _has_aborted = false; }
bool claimed() { return _claimed; }
void set_oop_closure(OopClosure* oop_closure) {
_oop_closure = oop_closure;
}
// It grays the object by marking it and, if necessary, pushing it
// on the local queue
void deal_with_reference(oop obj);
// It scans an object and visits its children.
void scan_object(oop obj) {
tmp_guarantee_CM( _nextMarkBitMap->isMarked((HeapWord*) obj),
"invariant" );
if (_cm->verbose_high())
gclog_or_tty->print_cr("[%d] we're scanning object "PTR_FORMAT,
_task_id, (void*) obj);
size_t obj_size = obj->size();
_words_scanned += obj_size;
obj->oop_iterate(_oop_closure);
statsOnly( ++_objs_scanned );
check_limits();
}
// It pushes an object on the local queue.
void push(oop obj);
// These two move entries to/from the global stack.
void move_entries_to_global_stack();
void get_entries_from_global_stack();
// It pops and scans objects from the local queue. If partially is
// true, then it stops when the queue size is of a given limit. If
// partially is false, then it stops when the queue is empty.
void drain_local_queue(bool partially);
// It moves entries from the global stack to the local queue and
// drains the local queue. If partially is true, then it stops when
// both the global stack and the local queue reach a given size. If
// partially if false, it tries to empty them totally.
void drain_global_stack(bool partially);
// It keeps picking SATB buffers and processing them until no SATB
// buffers are available.
void drain_satb_buffers();
// It keeps popping regions from the region stack and processing
// them until the region stack is empty.
void drain_region_stack(BitMapClosure* closure);
// moves the local finger to a new location
inline void move_finger_to(HeapWord* new_finger) {
tmp_guarantee_CM( new_finger >= _finger && new_finger < _region_limit,
"invariant" );
_finger = new_finger;
}
// moves the region finger to a new location
inline void move_region_finger_to(HeapWord* new_finger) {
tmp_guarantee_CM( new_finger < _cm->finger(), "invariant" );
_region_finger = new_finger;
}
CMTask(int task_num, ConcurrentMark *cm,
CMTaskQueue* task_queue, CMTaskQueueSet* task_queues);
// it prints statistics associated with this task
void print_stats();
#if _MARKING_STATS_
void increase_objs_found_on_bitmap() { ++_objs_found_on_bitmap; }
#endif // _MARKING_STATS_
};