8159422: Very high Concurrent Mark mark stack contention
Summary: Decrease contention on mark stack by splitting locks, and minimizing the amount of time these locks are held. Improve mark stack management.
Reviewed-by: kbarrett, mgerdin, eosterlund
/*
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#ifndef SHARE_VM_GC_G1_G1CONCURRENTMARK_HPP
#define SHARE_VM_GC_G1_G1CONCURRENTMARK_HPP
#include "classfile/javaClasses.hpp"
#include "gc/g1/g1RegionToSpaceMapper.hpp"
#include "gc/g1/heapRegionSet.hpp"
#include "gc/shared/taskqueue.hpp"
class G1CollectedHeap;
class G1CMBitMap;
class G1CMTask;
class G1ConcurrentMark;
class ConcurrentGCTimer;
class G1OldTracer;
class G1SurvivorRegions;
typedef GenericTaskQueue<oop, mtGC> G1CMTaskQueue;
typedef GenericTaskQueueSet<G1CMTaskQueue, mtGC> G1CMTaskQueueSet;
// Closure used by CM during concurrent reference discovery
// and reference processing (during remarking) to determine
// if a particular object is alive. It is primarily used
// to determine if referents of discovered reference objects
// are alive. An instance is also embedded into the
// reference processor as the _is_alive_non_header field
class G1CMIsAliveClosure: public BoolObjectClosure {
G1CollectedHeap* _g1;
public:
G1CMIsAliveClosure(G1CollectedHeap* g1) : _g1(g1) { }
bool do_object_b(oop obj);
};
// A generic CM bit map. This is essentially a wrapper around the BitMap
// class, with one bit per (1<<_shifter) HeapWords.
class G1CMBitMapRO VALUE_OBJ_CLASS_SPEC {
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
BitMapView _bm; // the bit map itself
public:
// constructor
G1CMBitMapRO(int shifter);
// inquiries
HeapWord* startWord() const { return _bmStartWord; }
// 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
inline 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(const HeapWord* addr,
const HeapWord* limit = NULL) const;
// conversion utilities
HeapWord* offsetToHeapWord(size_t offset) const {
return _bmStartWord + (offset << _shifter);
}
size_t heapWordToOffset(const HeapWord* addr) const {
return pointer_delta(addr, _bmStartWord) >> _shifter;
}
// The argument addr should be the start address of a valid object
inline HeapWord* nextObject(HeapWord* addr);
void print_on_error(outputStream* st, const char* prefix) const;
// debugging
NOT_PRODUCT(bool covers(MemRegion rs) const;)
};
class G1CMBitMapMappingChangedListener : public G1MappingChangedListener {
private:
G1CMBitMap* _bm;
public:
G1CMBitMapMappingChangedListener() : _bm(NULL) {}
void set_bitmap(G1CMBitMap* bm) { _bm = bm; }
virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled);
};
class G1CMBitMap : public G1CMBitMapRO {
private:
G1CMBitMapMappingChangedListener _listener;
public:
static size_t compute_size(size_t heap_size);
// Returns the amount of bytes on the heap between two marks in the bitmap.
static size_t mark_distance();
// Returns how many bytes (or bits) of the heap a single byte (or bit) of the
// mark bitmap corresponds to. This is the same as the mark distance above.
static size_t heap_map_factor() {
return mark_distance();
}
G1CMBitMap() : G1CMBitMapRO(LogMinObjAlignment), _listener() { _listener.set_bitmap(this); }
// Initializes the underlying BitMap to cover the given area.
void initialize(MemRegion heap, G1RegionToSpaceMapper* storage);
// Write marks.
inline void mark(HeapWord* addr);
inline void clear(HeapWord* addr);
inline bool parMark(HeapWord* addr);
void clear_range(MemRegion mr);
};
// Represents the overflow mark stack used by concurrent marking.
//
// Stores oops in a huge buffer in virtual memory that is always fully committed.
// Resizing may only happen during a STW pause when the stack is empty.
//
// Memory is allocated on a "chunk" basis, i.e. a set of oops. For this, the mark
// stack memory is split into evenly sized chunks of oops. Users can only
// add or remove entries on that basis.
// Chunks are filled in increasing address order. Not completely filled chunks
// have a NULL element as a terminating element.
//
// Every chunk has a header containing a single pointer element used for memory
// management. This wastes some space, but is negligible (< .1% with current sizing).
//
// Memory management is done using a mix of tracking a high water-mark indicating
// that all chunks at a lower address are valid chunks, and a singly linked free
// list connecting all empty chunks.
class G1CMMarkStack VALUE_OBJ_CLASS_SPEC {
public:
// Number of oops that can fit in a single chunk.
static const size_t OopsPerChunk = 1024 - 1 /* One reference for the next pointer */;
private:
struct OopChunk {
OopChunk* next;
oop data[OopsPerChunk];
};
size_t _max_chunk_capacity; // Maximum number of OopChunk elements on the stack.
OopChunk* _base; // Bottom address of allocated memory area.
size_t _chunk_capacity; // Current maximum number of OopChunk elements.
char _pad0[DEFAULT_CACHE_LINE_SIZE];
OopChunk* volatile _free_list; // Linked list of free chunks that can be allocated by users.
char _pad1[DEFAULT_CACHE_LINE_SIZE - sizeof(OopChunk*)];
OopChunk* volatile _chunk_list; // List of chunks currently containing data.
volatile size_t _chunks_in_chunk_list;
char _pad2[DEFAULT_CACHE_LINE_SIZE - sizeof(OopChunk*) - sizeof(size_t)];
volatile size_t _hwm; // High water mark within the reserved space.
char _pad4[DEFAULT_CACHE_LINE_SIZE - sizeof(size_t)];
// Allocate a new chunk from the reserved memory, using the high water mark. Returns
// NULL if out of memory.
OopChunk* allocate_new_chunk();
volatile bool _out_of_memory;
// Atomically add the given chunk to the list.
void add_chunk_to_list(OopChunk* volatile* list, OopChunk* elem);
// Atomically remove and return a chunk from the given list. Returns NULL if the
// list is empty.
OopChunk* remove_chunk_from_list(OopChunk* volatile* list);
void add_chunk_to_chunk_list(OopChunk* elem);
void add_chunk_to_free_list(OopChunk* elem);
OopChunk* remove_chunk_from_chunk_list();
OopChunk* remove_chunk_from_free_list();
bool _should_expand;
// Resizes the mark stack to the given new capacity. Releases any previous
// memory if successful.
bool resize(size_t new_capacity);
public:
G1CMMarkStack();
~G1CMMarkStack();
// Alignment and minimum capacity of this mark stack in number of oops.
static size_t capacity_alignment();
// Allocate and initialize the mark stack with the given number of oops.
bool initialize(size_t initial_capacity, size_t max_capacity);
// Pushes the given buffer containing at most OopsPerChunk elements on the mark
// stack. If less than OopsPerChunk elements are to be pushed, the array must
// be terminated with a NULL.
// Returns whether the buffer contents were successfully pushed to the global mark
// stack.
bool par_push_chunk(oop* buffer);
// Pops a chunk from this mark stack, copying them into the given buffer. This
// chunk may contain up to OopsPerChunk elements. If there are less, the last
// element in the array is a NULL pointer.
bool par_pop_chunk(oop* buffer);
// Return whether the chunk list is empty. Racy due to unsynchronized access to
// _chunk_list.
bool is_empty() const { return _chunk_list == NULL; }
size_t capacity() const { return _chunk_capacity; }
bool is_out_of_memory() const { return _out_of_memory; }
void clear_out_of_memory() { _out_of_memory = false; }
bool should_expand() const { return _should_expand; }
void set_should_expand(bool value) { _should_expand = value; }
// Expand the stack, typically in response to an overflow condition
void expand();
// Return the approximate number of oops on this mark stack. Racy due to
// unsynchronized access to _chunks_in_chunk_list.
size_t size() const { return _chunks_in_chunk_list * OopsPerChunk; }
void set_empty();
// Apply Fn to every oop on the mark stack. The mark stack must not
// be modified while iterating.
template<typename Fn> void iterate(Fn fn) const PRODUCT_RETURN;
};
// Root Regions are regions that are not empty at the beginning of a
// marking cycle and which we might collect during an evacuation pause
// while the cycle is active. Given that, during evacuation pauses, we
// do not copy objects that are explicitly marked, what we have to do
// for the root regions is to scan them and mark all objects reachable
// from them. According to the SATB assumptions, we only need to visit
// each object once during marking. So, as long as we finish this scan
// before the next evacuation pause, we can copy the objects from the
// root regions without having to mark them or do anything else to them.
//
// Currently, we only support root region scanning once (at the start
// of the marking cycle) and the root regions are all the survivor
// regions populated during the initial-mark pause.
class G1CMRootRegions VALUE_OBJ_CLASS_SPEC {
private:
const G1SurvivorRegions* _survivors;
G1ConcurrentMark* _cm;
volatile bool _scan_in_progress;
volatile bool _should_abort;
volatile int _claimed_survivor_index;
void notify_scan_done();
public:
G1CMRootRegions();
// We actually do most of the initialization in this method.
void init(const G1SurvivorRegions* survivors, G1ConcurrentMark* cm);
// Reset the claiming / scanning of the root regions.
void prepare_for_scan();
// Forces get_next() to return NULL so that the iteration aborts early.
void abort() { _should_abort = true; }
// Return true if the CM thread are actively scanning root regions,
// false otherwise.
bool scan_in_progress() { return _scan_in_progress; }
// Claim the next root region to scan atomically, or return NULL if
// all have been claimed.
HeapRegion* claim_next();
// The number of root regions to scan.
uint num_root_regions() const;
void cancel_scan();
// Flag that we're done with root region scanning and notify anyone
// who's waiting on it. If aborted is false, assume that all regions
// have been claimed.
void scan_finished();
// If CM threads are still scanning root regions, wait until they
// are done. Return true if we had to wait, false otherwise.
bool wait_until_scan_finished();
};
class ConcurrentMarkThread;
class G1ConcurrentMark: public CHeapObj<mtGC> {
friend class ConcurrentMarkThread;
friend class G1ParNoteEndTask;
friend class G1VerifyLiveDataClosure;
friend class G1CMRefProcTaskProxy;
friend class G1CMRefProcTaskExecutor;
friend class G1CMKeepAliveAndDrainClosure;
friend class G1CMDrainMarkingStackClosure;
friend class G1CMBitMapClosure;
friend class G1CMConcurrentMarkingTask;
friend class G1CMRemarkTask;
friend class G1CMTask;
protected:
ConcurrentMarkThread* _cmThread; // The thread doing the work
G1CollectedHeap* _g1h; // The heap
uint _parallel_marking_threads; // The number of marking
// threads we're using
uint _max_parallel_marking_threads; // Max number of marking
// threads we'll ever 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
FreeRegionList _cleanup_list;
// Concurrent marking support structures
G1CMBitMap _markBitMap1;
G1CMBitMap _markBitMap2;
G1CMBitMapRO* _prevMarkBitMap; // Completed mark bitmap
G1CMBitMap* _nextMarkBitMap; // Under-construction mark bitmap
// Heap bounds
HeapWord* _heap_start;
HeapWord* _heap_end;
// Root region tracking and claiming
G1CMRootRegions _root_regions;
// For gray objects
G1CMMarkStack _global_mark_stack; // Grey objects behind global finger
HeapWord* volatile _finger; // The global finger, region aligned,
// always points to the end of the
// last claimed region
// Marking tasks
uint _max_worker_id;// Maximum worker id
uint _active_tasks; // Task num currently active
G1CMTask** _tasks; // Task queue array (max_worker_id len)
G1CMTaskQueueSet* _task_queues; // Task queue set
ParallelTaskTerminator _terminator; // For termination
// Two sync barriers that are used to synchronize 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-initialize
// their data structures and task 0 re-initializes 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-initialized. 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;
ConcurrentGCTimer* _gc_timer_cm;
G1OldTracer* _gc_tracer_cm;
// 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 weakRefsWorkParallelPart(BoolObjectClosure* is_alive, bool purged_classes);
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();
// Resets all the marking data structures. Called when we have to restart
// marking or when marking completes (via set_non_marking_state below).
void reset_marking_state(bool clear_overflow = true);
// We do this after we're done with marking so that the marking data
// structures are initialized to a sensible and predictable state.
void set_non_marking_state();
// Called to indicate how many threads are currently active.
void set_concurrency(uint active_tasks);
// It should be called to indicate which phase we're in (concurrent
// mark or remark) and how many threads are currently active.
void set_concurrency_and_phase(uint active_tasks, bool concurrent);
// Prints all gathered CM-related statistics
void print_stats();
bool cleanup_list_is_empty() {
return _cleanup_list.is_empty();
}
// Accessor methods
uint parallel_marking_threads() const { return _parallel_marking_threads; }
uint max_parallel_marking_threads() const { return _max_parallel_marking_threads;}
double sleep_factor() { return _sleep_factor; }
double marking_task_overhead() { return _marking_task_overhead;}
HeapWord* finger() { return _finger; }
bool concurrent() { return _concurrent; }
uint active_tasks() { return _active_tasks; }
ParallelTaskTerminator* terminator() { return &_terminator; }
// It claims the next available region to be scanned by a marking
// task/thread. 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(uint worker_id);
// It determines whether we've run out of regions to scan. Note that
// the finger can point past the heap end in case the heap was expanded
// to satisfy an allocation without doing a GC. This is fine, because all
// objects in those regions will be considered live anyway because of
// SATB guarantees (i.e. their TAMS will be equal to bottom).
bool out_of_regions() { return _finger >= _heap_end; }
// Returns the task with the given id
G1CMTask* task(int id) {
assert(0 <= id && id < (int) _active_tasks,
"task id not within active bounds");
return _tasks[id];
}
// Returns the task queue with the given id
G1CMTaskQueue* task_queue(int id) {
assert(0 <= id && id < (int) _active_tasks,
"task queue id not within active bounds");
return (G1CMTaskQueue*) _task_queues->queue(id);
}
// Returns the task queue set
G1CMTaskQueueSet* task_queues() { return _task_queues; }
// Access / manipulation of the overflow flag which is set to
// indicate that the global stack has overflown
bool has_overflown() { return _has_overflown; }
void set_has_overflown() { _has_overflown = true; }
void clear_has_overflown() { _has_overflown = false; }
bool restart_for_overflow() { return _restart_for_overflow; }
// Methods to enter the two overflow sync barriers
void enter_first_sync_barrier(uint worker_id);
void enter_second_sync_barrier(uint worker_id);
// Card index of the bottom of the G1 heap. Used for biasing indices into
// the card bitmaps.
intptr_t _heap_bottom_card_num;
// Set to true when initialization is complete
bool _completed_initialization;
// end_timer, true to end gc timer after ending concurrent phase.
void register_concurrent_phase_end_common(bool end_timer);
// Clear the given bitmap in parallel using the given WorkGang. If may_yield is
// true, periodically insert checks to see if this method should exit prematurely.
void clear_bitmap(G1CMBitMap* bitmap, WorkGang* workers, bool may_yield);
public:
// Manipulation of the global mark stack.
// The push and pop operations are used by tasks for transfers
// between task-local queues and the global mark stack.
bool mark_stack_push(oop* arr) {
if (!_global_mark_stack.par_push_chunk(arr)) {
set_has_overflown();
return false;
}
return true;
}
bool mark_stack_pop(oop* arr) {
return _global_mark_stack.par_pop_chunk(arr);
}
size_t mark_stack_size() { return _global_mark_stack.size(); }
size_t partial_mark_stack_size_target() { return _global_mark_stack.capacity()/3; }
bool mark_stack_overflow() { return _global_mark_stack.is_out_of_memory(); }
bool mark_stack_empty() { return _global_mark_stack.is_empty(); }
G1CMRootRegions* root_regions() { return &_root_regions; }
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 concurrent_cycle_start();
void concurrent_cycle_end();
void update_accum_task_vtime(int i, double vtime) {
_accum_task_vtime[i] += vtime;
}
double all_task_accum_vtime() {
double ret = 0.0;
for (uint i = 0; i < _max_worker_id; ++i)
ret += _accum_task_vtime[i];
return ret;
}
// Attempts to steal an object from the task queues of other tasks
bool try_stealing(uint worker_id, int* hash_seed, oop& obj);
G1ConcurrentMark(G1CollectedHeap* g1h,
G1RegionToSpaceMapper* prev_bitmap_storage,
G1RegionToSpaceMapper* next_bitmap_storage);
~G1ConcurrentMark();
ConcurrentMarkThread* cmThread() { return _cmThread; }
G1CMBitMapRO* prevMarkBitMap() const { return _prevMarkBitMap; }
G1CMBitMap* nextMarkBitMap() const { return _nextMarkBitMap; }
// Returns the number of GC threads to be used in a concurrent
// phase based on the number of GC threads being used in a STW
// phase.
uint scale_parallel_threads(uint n_par_threads);
// Calculates the number of GC threads to be used in a concurrent phase.
uint calc_parallel_marking_threads();
// The following three are interaction between CM and
// G1CollectedHeap
// This notifies CM that a root during initial-mark needs to be
// grayed. It is MT-safe. hr is the region that
// contains the object and it's passed optionally from callers who
// might already have it (no point in recalculating it).
inline void grayRoot(oop obj,
HeapRegion* hr = NULL);
// Prepare internal data structures for the next mark cycle. This includes clearing
// the next mark bitmap and some internal data structures. This method is intended
// to be called concurrently to the mutator. It will yield to safepoint requests.
void cleanup_for_next_mark();
// Clear the previous marking bitmap during safepoint.
void clear_prev_bitmap(WorkGang* workers);
// Return whether the next mark bitmap has no marks set. To be used for assertions
// only. Will not yield to pause requests.
bool nextMarkBitmapIsClear();
// 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();
// Scan all the root regions and mark everything reachable from
// them.
void scan_root_regions();
// Scan a single root region and mark everything reachable from it.
void scanRootRegion(HeapRegion* hr);
// Do concurrent phase of marking, to a tentative transitive closure.
void mark_from_roots();
void checkpointRootsFinal(bool clear_all_soft_refs);
void checkpointRootsFinalWork();
void cleanup();
void complete_cleanup();
// Mark in the previous bitmap. NB: this is usually read-only, so use
// this carefully!
inline void markPrev(oop p);
// Clears marks for all objects in the given range, for the prev or
// next bitmaps. NB: the previous bitmap is usually
// read-only, so use this carefully!
void clearRangePrevBitmap(MemRegion mr);
// Verify that there are no CSet oops on the stacks (taskqueues /
// global mark stack) and fingers (global / per-task).
// If marking is not in progress, it's a no-op.
void verify_no_cset_oops() PRODUCT_RETURN;
inline bool isPrevMarked(oop p) const;
inline bool do_yield_check();
// Abandon current marking iteration due to a Full GC.
void abort();
bool has_aborted() { return _has_aborted; }
void print_summary_info();
void print_worker_threads_on(outputStream* st) const;
void threads_do(ThreadClosure* tc) const;
void print_on_error(outputStream* st) const;
// Attempts to mark the given object on the next mark bitmap.
inline bool par_mark(oop obj);
// Returns true if initialization was successfully completed.
bool completed_initialization() const {
return _completed_initialization;
}
ConcurrentGCTimer* gc_timer_cm() const { return _gc_timer_cm; }
G1OldTracer* gc_tracer_cm() const { return _gc_tracer_cm; }
private:
// Clear (Reset) all liveness count data.
void clear_live_data(WorkGang* workers);
#ifdef ASSERT
// Verify all of the above data structures that they are in initial state.
void verify_live_data_clear();
#endif
// Aggregates the per-card liveness data based on the current marking. Also sets
// the amount of marked bytes for each region.
void create_live_data();
void finalize_live_data();
void verify_live_data();
};
// A class representing a marking task.
class G1CMTask : 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
};
uint _worker_id;
G1CollectedHeap* _g1h;
G1ConcurrentMark* _cm;
G1CMBitMap* _nextMarkBitMap;
// the task queue of this task
G1CMTaskQueue* _task_queue;
private:
// the task queue set---needed for stealing
G1CMTaskQueueSet* _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;
// 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
G1CMOopClosure* _cm_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;
// 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_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;
// 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();
// 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; }
// Test whether obj might have already been passed over by the
// mark bitmap scan, and so needs to be pushed onto the mark stack.
bool is_below_finger(oop obj, HeapWord* global_finger) const;
template<bool scan> void process_grey_object(oop obj);
public:
// It resets the task; it should be called right at the beginning of
// a marking phase.
void reset(G1CMBitMap* _nextMarkBitMap);
// it clears all the fields that correspond to a claimed region.
void clear_region_fields();
void set_concurrent(bool concurrent) { _concurrent = concurrent; }
// 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,
bool do_termination,
bool is_serial);
// 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 worker ID associated with this task.
uint worker_id() { return _worker_id; }
// From TerminatorTerminator. It determines whether this task should
// exit the termination protocol after it's entered it.
virtual bool should_exit_termination();
// Resets the local region fields after a task has finished scanning a
// region; or when they have become stale as a result of the region
// being evacuated.
void giveup_current_region();
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 has_timed_out() { return _has_timed_out; }
bool claimed() { return _claimed; }
void set_cm_oop_closure(G1CMOopClosure* cm_oop_closure);
// Increment the number of references this task has visited.
void increment_refs_reached() { ++_refs_reached; }
// Grey the object by marking it. If not already marked, push it on
// the local queue if below the finger.
// obj is below its region's NTAMS.
inline void make_reference_grey(oop obj);
// Grey the object (by calling make_grey_reference) if required,
// e.g. obj is below its containing region's NTAMS.
// Precondition: obj is a valid heap object.
inline void deal_with_reference(oop obj);
// It scans an object and visits its children.
inline void scan_object(oop obj);
// It pushes an object on the local queue.
inline void push(oop obj);
// Move entries to the global stack.
void move_entries_to_global_stack();
// Move entries from the global stack, return true if we were successful to do so.
bool 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();
// moves the local finger to a new location
inline void move_finger_to(HeapWord* new_finger) {
assert(new_finger >= _finger && new_finger < _region_limit, "invariant");
_finger = new_finger;
}
G1CMTask(uint worker_id,
G1ConcurrentMark *cm,
G1CMTaskQueue* task_queue,
G1CMTaskQueueSet* task_queues);
// it prints statistics associated with this task
void print_stats();
};
// Class that's used to to print out per-region liveness
// information. It's currently used at the end of marking and also
// after we sort the old regions at the end of the cleanup operation.
class G1PrintRegionLivenessInfoClosure: public HeapRegionClosure {
private:
// Accumulators for these values.
size_t _total_used_bytes;
size_t _total_capacity_bytes;
size_t _total_prev_live_bytes;
size_t _total_next_live_bytes;
// Accumulator for the remembered set size
size_t _total_remset_bytes;
// Accumulator for strong code roots memory size
size_t _total_strong_code_roots_bytes;
static double perc(size_t val, size_t total) {
if (total == 0) {
return 0.0;
} else {
return 100.0 * ((double) val / (double) total);
}
}
static double bytes_to_mb(size_t val) {
return (double) val / (double) M;
}
public:
// The header and footer are printed in the constructor and
// destructor respectively.
G1PrintRegionLivenessInfoClosure(const char* phase_name);
virtual bool doHeapRegion(HeapRegion* r);
~G1PrintRegionLivenessInfoClosure();
};
#endif // SHARE_VM_GC_G1_G1CONCURRENTMARK_HPP