6994297: G1: do first-level slow-path allocations with a CAS
Summary: First attempt to allocate out the current alloc region using a CAS instead of taking the Heap_lock (first level of G1's slow allocation path). Only if that fails and it's necessary to replace the current alloc region take the Heap_lock (that's the second level of G1's slow allocation path).
Reviewed-by: johnc, brutisso, ysr
/*
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* 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.
*
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* 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).
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* 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
#ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTEDHEAP_HPP
#define SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTEDHEAP_HPP
#include "gc_implementation/g1/concurrentMark.hpp"
#include "gc_implementation/g1/g1RemSet.hpp"
#include "gc_implementation/g1/heapRegion.hpp"
#include "gc_implementation/parNew/parGCAllocBuffer.hpp"
#include "memory/barrierSet.hpp"
#include "memory/memRegion.hpp"
#include "memory/sharedHeap.hpp"
// A "G1CollectedHeap" is an implementation of a java heap for HotSpot.
// It uses the "Garbage First" heap organization and algorithm, which
// may combine concurrent marking with parallel, incremental compaction of
// heap subsets that will yield large amounts of garbage.
class HeapRegion;
class HeapRegionSeq;
class PermanentGenerationSpec;
class GenerationSpec;
class OopsInHeapRegionClosure;
class G1ScanHeapEvacClosure;
class ObjectClosure;
class SpaceClosure;
class CompactibleSpaceClosure;
class Space;
class G1CollectorPolicy;
class GenRemSet;
class G1RemSet;
class HeapRegionRemSetIterator;
class ConcurrentMark;
class ConcurrentMarkThread;
class ConcurrentG1Refine;
class ConcurrentZFThread;
typedef OverflowTaskQueue<StarTask> RefToScanQueue;
typedef GenericTaskQueueSet<RefToScanQueue> RefToScanQueueSet;
typedef int RegionIdx_t; // needs to hold [ 0..max_regions() )
typedef int CardIdx_t; // needs to hold [ 0..CardsPerRegion )
enum G1GCThreadGroups {
G1CRGroup = 0,
G1ZFGroup = 1,
G1CMGroup = 2,
G1CLGroup = 3
};
enum GCAllocPurpose {
GCAllocForTenured,
GCAllocForSurvived,
GCAllocPurposeCount
};
class YoungList : public CHeapObj {
private:
G1CollectedHeap* _g1h;
HeapRegion* _head;
HeapRegion* _survivor_head;
HeapRegion* _survivor_tail;
HeapRegion* _curr;
size_t _length;
size_t _survivor_length;
size_t _last_sampled_rs_lengths;
size_t _sampled_rs_lengths;
void empty_list(HeapRegion* list);
public:
YoungList(G1CollectedHeap* g1h);
void push_region(HeapRegion* hr);
void add_survivor_region(HeapRegion* hr);
void empty_list();
bool is_empty() { return _length == 0; }
size_t length() { return _length; }
size_t survivor_length() { return _survivor_length; }
void rs_length_sampling_init();
bool rs_length_sampling_more();
void rs_length_sampling_next();
void reset_sampled_info() {
_last_sampled_rs_lengths = 0;
}
size_t sampled_rs_lengths() { return _last_sampled_rs_lengths; }
// for development purposes
void reset_auxilary_lists();
void clear() { _head = NULL; _length = 0; }
void clear_survivors() {
_survivor_head = NULL;
_survivor_tail = NULL;
_survivor_length = 0;
}
HeapRegion* first_region() { return _head; }
HeapRegion* first_survivor_region() { return _survivor_head; }
HeapRegion* last_survivor_region() { return _survivor_tail; }
// debugging
bool check_list_well_formed();
bool check_list_empty(bool check_sample = true);
void print();
};
class RefineCardTableEntryClosure;
class G1CollectedHeap : public SharedHeap {
friend class VM_G1CollectForAllocation;
friend class VM_GenCollectForPermanentAllocation;
friend class VM_G1CollectFull;
friend class VM_G1IncCollectionPause;
friend class VMStructs;
// Closures used in implementation.
friend class G1ParCopyHelper;
friend class G1IsAliveClosure;
friend class G1EvacuateFollowersClosure;
friend class G1ParScanThreadState;
friend class G1ParScanClosureSuper;
friend class G1ParEvacuateFollowersClosure;
friend class G1ParTask;
friend class G1FreeGarbageRegionClosure;
friend class RefineCardTableEntryClosure;
friend class G1PrepareCompactClosure;
friend class RegionSorter;
friend class CountRCClosure;
friend class EvacPopObjClosure;
friend class G1ParCleanupCTTask;
// Other related classes.
friend class G1MarkSweep;
private:
// The one and only G1CollectedHeap, so static functions can find it.
static G1CollectedHeap* _g1h;
static size_t _humongous_object_threshold_in_words;
// Storage for the G1 heap (excludes the permanent generation).
VirtualSpace _g1_storage;
MemRegion _g1_reserved;
// The part of _g1_storage that is currently committed.
MemRegion _g1_committed;
// The maximum part of _g1_storage that has ever been committed.
MemRegion _g1_max_committed;
// The number of regions that are completely free.
size_t _free_regions;
// The number of regions we could create by expansion.
size_t _expansion_regions;
// Return the number of free regions in the heap (by direct counting.)
size_t count_free_regions();
// Return the number of free regions on the free and unclean lists.
size_t count_free_regions_list();
// The block offset table for the G1 heap.
G1BlockOffsetSharedArray* _bot_shared;
// Move all of the regions off the free lists, then rebuild those free
// lists, before and after full GC.
void tear_down_region_lists();
void rebuild_region_lists();
// This sets all non-empty regions to need zero-fill (which they will if
// they are empty after full collection.)
void set_used_regions_to_need_zero_fill();
// The sequence of all heap regions in the heap.
HeapRegionSeq* _hrs;
// The region from which normal-sized objects are currently being
// allocated. May be NULL.
HeapRegion* _cur_alloc_region;
// Postcondition: cur_alloc_region == NULL.
void abandon_cur_alloc_region();
void abandon_gc_alloc_regions();
// The to-space memory regions into which objects are being copied during
// a GC.
HeapRegion* _gc_alloc_regions[GCAllocPurposeCount];
size_t _gc_alloc_region_counts[GCAllocPurposeCount];
// These are the regions, one per GCAllocPurpose, that are half-full
// at the end of a collection and that we want to reuse during the
// next collection.
HeapRegion* _retained_gc_alloc_regions[GCAllocPurposeCount];
// This specifies whether we will keep the last half-full region at
// the end of a collection so that it can be reused during the next
// collection (this is specified per GCAllocPurpose)
bool _retain_gc_alloc_region[GCAllocPurposeCount];
// A list of the regions that have been set to be alloc regions in the
// current collection.
HeapRegion* _gc_alloc_region_list;
// Determines PLAB size for a particular allocation purpose.
static size_t desired_plab_sz(GCAllocPurpose purpose);
// When called by par thread, require par_alloc_during_gc_lock() to be held.
void push_gc_alloc_region(HeapRegion* hr);
// This should only be called single-threaded. Undeclares all GC alloc
// regions.
void forget_alloc_region_list();
// Should be used to set an alloc region, because there's other
// associated bookkeeping.
void set_gc_alloc_region(int purpose, HeapRegion* r);
// Check well-formedness of alloc region list.
bool check_gc_alloc_regions();
// Outside of GC pauses, the number of bytes used in all regions other
// than the current allocation region.
size_t _summary_bytes_used;
// This is used for a quick test on whether a reference points into
// the collection set or not. Basically, we have an array, with one
// byte per region, and that byte denotes whether the corresponding
// region is in the collection set or not. The entry corresponding
// the bottom of the heap, i.e., region 0, is pointed to by
// _in_cset_fast_test_base. The _in_cset_fast_test field has been
// biased so that it actually points to address 0 of the address
// space, to make the test as fast as possible (we can simply shift
// the address to address into it, instead of having to subtract the
// bottom of the heap from the address before shifting it; basically
// it works in the same way the card table works).
bool* _in_cset_fast_test;
// The allocated array used for the fast test on whether a reference
// points into the collection set or not. This field is also used to
// free the array.
bool* _in_cset_fast_test_base;
// The length of the _in_cset_fast_test_base array.
size_t _in_cset_fast_test_length;
volatile unsigned _gc_time_stamp;
size_t* _surviving_young_words;
void setup_surviving_young_words();
void update_surviving_young_words(size_t* surv_young_words);
void cleanup_surviving_young_words();
// It decides whether an explicit GC should start a concurrent cycle
// instead of doing a STW GC. Currently, a concurrent cycle is
// explicitly started if:
// (a) cause == _gc_locker and +GCLockerInvokesConcurrent, or
// (b) cause == _java_lang_system_gc and +ExplicitGCInvokesConcurrent.
bool should_do_concurrent_full_gc(GCCause::Cause cause);
// Keeps track of how many "full collections" (i.e., Full GCs or
// concurrent cycles) we have completed. The number of them we have
// started is maintained in _total_full_collections in CollectedHeap.
volatile unsigned int _full_collections_completed;
// These are macros so that, if the assert fires, we get the correct
// line number, file, etc.
#define heap_locking_asserts_err_msg(__extra_message) \
err_msg("%s : Heap_lock %slocked, %sat a safepoint", \
(__extra_message), \
(!Heap_lock->owned_by_self()) ? "NOT " : "", \
(!SafepointSynchronize::is_at_safepoint()) ? "NOT " : "")
#define assert_heap_locked() \
do { \
assert(Heap_lock->owned_by_self(), \
heap_locking_asserts_err_msg("should be holding the Heap_lock")); \
} while (0)
#define assert_heap_locked_or_at_safepoint() \
do { \
assert(Heap_lock->owned_by_self() || \
SafepointSynchronize::is_at_safepoint(), \
heap_locking_asserts_err_msg("should be holding the Heap_lock or " \
"should be at a safepoint")); \
} while (0)
#define assert_heap_locked_and_not_at_safepoint() \
do { \
assert(Heap_lock->owned_by_self() && \
!SafepointSynchronize::is_at_safepoint(), \
heap_locking_asserts_err_msg("should be holding the Heap_lock and " \
"should not be at a safepoint")); \
} while (0)
#define assert_heap_not_locked() \
do { \
assert(!Heap_lock->owned_by_self(), \
heap_locking_asserts_err_msg("should not be holding the Heap_lock")); \
} while (0)
#define assert_heap_not_locked_and_not_at_safepoint() \
do { \
assert(!Heap_lock->owned_by_self() && \
!SafepointSynchronize::is_at_safepoint(), \
heap_locking_asserts_err_msg("should not be holding the Heap_lock and " \
"should not be at a safepoint")); \
} while (0)
#define assert_at_safepoint() \
do { \
assert(SafepointSynchronize::is_at_safepoint(), \
heap_locking_asserts_err_msg("should be at a safepoint")); \
} while (0)
#define assert_not_at_safepoint() \
do { \
assert(!SafepointSynchronize::is_at_safepoint(), \
heap_locking_asserts_err_msg("should not be at a safepoint")); \
} while (0)
protected:
// Returns "true" iff none of the gc alloc regions have any allocations
// since the last call to "save_marks".
bool all_alloc_regions_no_allocs_since_save_marks();
// Perform finalization stuff on all allocation regions.
void retire_all_alloc_regions();
// The number of regions allocated to hold humongous objects.
int _num_humongous_regions;
YoungList* _young_list;
// The current policy object for the collector.
G1CollectorPolicy* _g1_policy;
// Parallel allocation lock to protect the current allocation region.
Mutex _par_alloc_during_gc_lock;
Mutex* par_alloc_during_gc_lock() { return &_par_alloc_during_gc_lock; }
// If possible/desirable, allocate a new HeapRegion for normal object
// allocation sufficient for an allocation of the given "word_size".
// If "do_expand" is true, will attempt to expand the heap if necessary
// to to satisfy the request. If "zero_filled" is true, requires a
// zero-filled region.
// (Returning NULL will trigger a GC.)
virtual HeapRegion* newAllocRegion_work(size_t word_size,
bool do_expand,
bool zero_filled);
virtual HeapRegion* newAllocRegion(size_t word_size,
bool zero_filled = true) {
return newAllocRegion_work(word_size, false, zero_filled);
}
virtual HeapRegion* newAllocRegionWithExpansion(int purpose,
size_t word_size,
bool zero_filled = true);
// Attempt to allocate an object of the given (very large) "word_size".
// Returns "NULL" on failure.
virtual HeapWord* humongous_obj_allocate(size_t word_size);
// The following two methods, allocate_new_tlab() and
// mem_allocate(), are the two main entry points from the runtime
// into the G1's allocation routines. They have the following
// assumptions:
//
// * They should both be called outside safepoints.
//
// * They should both be called without holding the Heap_lock.
//
// * All allocation requests for new TLABs should go to
// allocate_new_tlab().
//
// * All non-TLAB allocation requests should go to mem_allocate()
// and mem_allocate() should never be called with is_tlab == true.
//
// * If the GC locker is active we currently stall until we can
// allocate a new young region. This will be changed in the
// near future (see CR 6994056).
//
// * If either call cannot satisfy the allocation request using the
// current allocating region, they will try to get a new one. If
// this fails, they will attempt to do an evacuation pause and
// retry the allocation.
//
// * If all allocation attempts fail, even after trying to schedule
// an evacuation pause, allocate_new_tlab() will return NULL,
// whereas mem_allocate() will attempt a heap expansion and/or
// schedule a Full GC.
//
// * We do not allow humongous-sized TLABs. So, allocate_new_tlab
// should never be called with word_size being humongous. All
// humongous allocation requests should go to mem_allocate() which
// will satisfy them with a special path.
virtual HeapWord* allocate_new_tlab(size_t word_size);
virtual HeapWord* mem_allocate(size_t word_size,
bool is_noref,
bool is_tlab, /* expected to be false */
bool* gc_overhead_limit_was_exceeded);
// The following methods, allocate_from_cur_allocation_region(),
// attempt_allocation(), attempt_allocation_locked(),
// replace_cur_alloc_region_and_allocate(),
// attempt_allocation_slow(), and attempt_allocation_humongous()
// have very awkward pre- and post-conditions with respect to
// locking:
//
// If they are called outside a safepoint they assume the caller
// holds the Heap_lock when it calls them. However, on exit they
// will release the Heap_lock if they return a non-NULL result, but
// keep holding the Heap_lock if they return a NULL result. The
// reason for this is that we need to dirty the cards that span
// allocated blocks on young regions to avoid having to take the
// slow path of the write barrier (for performance reasons we don't
// update RSets for references whose source is a young region, so we
// don't need to look at dirty cards on young regions). But, doing
// this card dirtying while holding the Heap_lock can be a
// scalability bottleneck, especially given that some allocation
// requests might be of non-trivial size (and the larger the region
// size is, the fewer allocations requests will be considered
// humongous, as the humongous size limit is a fraction of the
// region size). So, when one of these calls succeeds in allocating
// a block it does the card dirtying after it releases the Heap_lock
// which is why it will return without holding it.
//
// The above assymetry is the reason why locking / unlocking is done
// explicitly (i.e., with Heap_lock->lock() and
// Heap_lock->unlocked()) instead of using MutexLocker and
// MutexUnlocker objects. The latter would ensure that the lock is
// unlocked / re-locked at every possible exit out of the basic
// block. However, we only want that action to happen in selected
// places.
//
// Further, if the above methods are called during a safepoint, then
// naturally there's no assumption about the Heap_lock being held or
// there's no attempt to unlock it. The parameter at_safepoint
// indicates whether the call is made during a safepoint or not (as
// an optimization, to avoid reading the global flag with
// SafepointSynchronize::is_at_safepoint()).
//
// The methods share these parameters:
//
// * word_size : the size of the allocation request in words
// * at_safepoint : whether the call is done at a safepoint; this
// also determines whether a GC is permitted
// (at_safepoint == false) or not (at_safepoint == true)
// * do_dirtying : whether the method should dirty the allocated
// block before returning
//
// They all return either the address of the block, if they
// successfully manage to allocate it, or NULL.
// It tries to satisfy an allocation request out of the current
// alloc region, which is passed as a parameter. It assumes that the
// caller has checked that the current alloc region is not NULL.
// Given that the caller has to check the current alloc region for
// at least NULL, it might as well pass it as the first parameter so
// that the method doesn't have to read it from the
// _cur_alloc_region field again. It is called from both
// attempt_allocation() and attempt_allocation_locked() and the
// with_heap_lock parameter indicates whether the caller was holding
// the heap lock when it called it or not.
inline HeapWord* allocate_from_cur_alloc_region(HeapRegion* cur_alloc_region,
size_t word_size,
bool with_heap_lock);
// First-level of allocation slow path: it attempts to allocate out
// of the current alloc region in a lock-free manner using a CAS. If
// that fails it takes the Heap_lock and calls
// attempt_allocation_locked() for the second-level slow path.
inline HeapWord* attempt_allocation(size_t word_size);
// Second-level of allocation slow path: while holding the Heap_lock
// it tries to allocate out of the current alloc region and, if that
// fails, tries to allocate out of a new current alloc region.
inline HeapWord* attempt_allocation_locked(size_t word_size);
// It assumes that the current alloc region has been retired and
// tries to allocate a new one. If it's successful, it performs the
// allocation out of the new current alloc region and updates
// _cur_alloc_region. Normally, it would try to allocate a new
// region if the young gen is not full, unless can_expand is true in
// which case it would always try to allocate a new region.
HeapWord* replace_cur_alloc_region_and_allocate(size_t word_size,
bool at_safepoint,
bool do_dirtying,
bool can_expand);
// Third-level of allocation slow path: when we are unable to
// allocate a new current alloc region to satisfy an allocation
// request (i.e., when attempt_allocation_locked() fails). It will
// try to do an evacuation pause, which might stall due to the GC
// locker, and retry the allocation attempt when appropriate.
HeapWord* attempt_allocation_slow(size_t word_size);
// The method that tries to satisfy a humongous allocation
// request. If it cannot satisfy it it will try to do an evacuation
// pause to perhaps reclaim enough space to be able to satisfy the
// allocation request afterwards.
HeapWord* attempt_allocation_humongous(size_t word_size,
bool at_safepoint);
// It does the common work when we are retiring the current alloc region.
inline void retire_cur_alloc_region_common(HeapRegion* cur_alloc_region);
// It retires the current alloc region, which is passed as a
// parameter (since, typically, the caller is already holding on to
// it). It sets _cur_alloc_region to NULL.
void retire_cur_alloc_region(HeapRegion* cur_alloc_region);
// It attempts to do an allocation immediately before or after an
// evacuation pause and can only be called by the VM thread. It has
// slightly different assumptions that the ones before (i.e.,
// assumes that the current alloc region has been retired).
HeapWord* attempt_allocation_at_safepoint(size_t word_size,
bool expect_null_cur_alloc_region);
// It dirties the cards that cover the block so that so that the post
// write barrier never queues anything when updating objects on this
// block. It is assumed (and in fact we assert) that the block
// belongs to a young region.
inline void dirty_young_block(HeapWord* start, size_t word_size);
// Allocate blocks during garbage collection. Will ensure an
// allocation region, either by picking one or expanding the
// heap, and then allocate a block of the given size. The block
// may not be a humongous - it must fit into a single heap region.
HeapWord* par_allocate_during_gc(GCAllocPurpose purpose, size_t word_size);
HeapWord* allocate_during_gc_slow(GCAllocPurpose purpose,
HeapRegion* alloc_region,
bool par,
size_t word_size);
// Ensure that no further allocations can happen in "r", bearing in mind
// that parallel threads might be attempting allocations.
void par_allocate_remaining_space(HeapRegion* r);
// Retires an allocation region when it is full or at the end of a
// GC pause.
void retire_alloc_region(HeapRegion* alloc_region, bool par);
// - if explicit_gc is true, the GC is for a System.gc() or a heap
// inspection request and should collect the entire heap
// - if clear_all_soft_refs is true, all soft references should be
// cleared during the GC
// - if explicit_gc is false, word_size describes the allocation that
// the GC should attempt (at least) to satisfy
// - it returns false if it is unable to do the collection due to the
// GC locker being active, true otherwise
bool do_collection(bool explicit_gc,
bool clear_all_soft_refs,
size_t word_size);
// Callback from VM_G1CollectFull operation.
// Perform a full collection.
void do_full_collection(bool clear_all_soft_refs);
// Resize the heap if necessary after a full collection. If this is
// after a collect-for allocation, "word_size" is the allocation size,
// and will be considered part of the used portion of the heap.
void resize_if_necessary_after_full_collection(size_t word_size);
// Callback from VM_G1CollectForAllocation operation.
// This function does everything necessary/possible to satisfy a
// failed allocation request (including collection, expansion, etc.)
HeapWord* satisfy_failed_allocation(size_t word_size, bool* succeeded);
// Attempting to expand the heap sufficiently
// to support an allocation of the given "word_size". If
// successful, perform the allocation and return the address of the
// allocated block, or else "NULL".
HeapWord* expand_and_allocate(size_t word_size);
public:
// Expand the garbage-first heap by at least the given size (in bytes!).
// (Rounds up to a HeapRegion boundary.)
virtual void expand(size_t expand_bytes);
// Do anything common to GC's.
virtual void gc_prologue(bool full);
virtual void gc_epilogue(bool full);
// We register a region with the fast "in collection set" test. We
// simply set to true the array slot corresponding to this region.
void register_region_with_in_cset_fast_test(HeapRegion* r) {
assert(_in_cset_fast_test_base != NULL, "sanity");
assert(r->in_collection_set(), "invariant");
int index = r->hrs_index();
assert(0 <= index && (size_t) index < _in_cset_fast_test_length, "invariant");
assert(!_in_cset_fast_test_base[index], "invariant");
_in_cset_fast_test_base[index] = true;
}
// This is a fast test on whether a reference points into the
// collection set or not. It does not assume that the reference
// points into the heap; if it doesn't, it will return false.
bool in_cset_fast_test(oop obj) {
assert(_in_cset_fast_test != NULL, "sanity");
if (_g1_committed.contains((HeapWord*) obj)) {
// no need to subtract the bottom of the heap from obj,
// _in_cset_fast_test is biased
size_t index = ((size_t) obj) >> HeapRegion::LogOfHRGrainBytes;
bool ret = _in_cset_fast_test[index];
// let's make sure the result is consistent with what the slower
// test returns
assert( ret || !obj_in_cs(obj), "sanity");
assert(!ret || obj_in_cs(obj), "sanity");
return ret;
} else {
return false;
}
}
void clear_cset_fast_test() {
assert(_in_cset_fast_test_base != NULL, "sanity");
memset(_in_cset_fast_test_base, false,
_in_cset_fast_test_length * sizeof(bool));
}
// This is called at the end of either a concurrent cycle or a Full
// GC to update the number of full collections completed. Those two
// can happen in a nested fashion, i.e., we start a concurrent
// cycle, a Full GC happens half-way through it which ends first,
// and then the cycle notices that a Full GC happened and ends
// too. The concurrent parameter is a boolean to help us do a bit
// tighter consistency checking in the method. If concurrent is
// false, the caller is the inner caller in the nesting (i.e., the
// Full GC). If concurrent is true, the caller is the outer caller
// in this nesting (i.e., the concurrent cycle). Further nesting is
// not currently supported. The end of the this call also notifies
// the FullGCCount_lock in case a Java thread is waiting for a full
// GC to happen (e.g., it called System.gc() with
// +ExplicitGCInvokesConcurrent).
void increment_full_collections_completed(bool concurrent);
unsigned int full_collections_completed() {
return _full_collections_completed;
}
protected:
// Shrink the garbage-first heap by at most the given size (in bytes!).
// (Rounds down to a HeapRegion boundary.)
virtual void shrink(size_t expand_bytes);
void shrink_helper(size_t expand_bytes);
#if TASKQUEUE_STATS
static void print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty);
void print_taskqueue_stats(outputStream* const st = gclog_or_tty) const;
void reset_taskqueue_stats();
#endif // TASKQUEUE_STATS
// Schedule the VM operation that will do an evacuation pause to
// satisfy an allocation request of word_size. *succeeded will
// return whether the VM operation was successful (it did do an
// evacuation pause) or not (another thread beat us to it or the GC
// locker was active). Given that we should not be holding the
// Heap_lock when we enter this method, we will pass the
// gc_count_before (i.e., total_collections()) as a parameter since
// it has to be read while holding the Heap_lock. Currently, both
// methods that call do_collection_pause() release the Heap_lock
// before the call, so it's easy to read gc_count_before just before.
HeapWord* do_collection_pause(size_t word_size,
unsigned int gc_count_before,
bool* succeeded);
// The guts of the incremental collection pause, executed by the vm
// thread. It returns false if it is unable to do the collection due
// to the GC locker being active, true otherwise
bool do_collection_pause_at_safepoint(double target_pause_time_ms);
// Actually do the work of evacuating the collection set.
void evacuate_collection_set();
// The g1 remembered set of the heap.
G1RemSet* _g1_rem_set;
// And it's mod ref barrier set, used to track updates for the above.
ModRefBarrierSet* _mr_bs;
// A set of cards that cover the objects for which the Rsets should be updated
// concurrently after the collection.
DirtyCardQueueSet _dirty_card_queue_set;
// The Heap Region Rem Set Iterator.
HeapRegionRemSetIterator** _rem_set_iterator;
// The closure used to refine a single card.
RefineCardTableEntryClosure* _refine_cte_cl;
// A function to check the consistency of dirty card logs.
void check_ct_logs_at_safepoint();
// A DirtyCardQueueSet that is used to hold cards that contain
// references into the current collection set. This is used to
// update the remembered sets of the regions in the collection
// set in the event of an evacuation failure.
DirtyCardQueueSet _into_cset_dirty_card_queue_set;
// After a collection pause, make the regions in the CS into free
// regions.
void free_collection_set(HeapRegion* cs_head);
// Abandon the current collection set without recording policy
// statistics or updating free lists.
void abandon_collection_set(HeapRegion* cs_head);
// Applies "scan_non_heap_roots" to roots outside the heap,
// "scan_rs" to roots inside the heap (having done "set_region" to
// indicate the region in which the root resides), and does "scan_perm"
// (setting the generation to the perm generation.) If "scan_rs" is
// NULL, then this step is skipped. The "worker_i"
// param is for use with parallel roots processing, and should be
// the "i" of the calling parallel worker thread's work(i) function.
// In the sequential case this param will be ignored.
void g1_process_strong_roots(bool collecting_perm_gen,
SharedHeap::ScanningOption so,
OopClosure* scan_non_heap_roots,
OopsInHeapRegionClosure* scan_rs,
OopsInGenClosure* scan_perm,
int worker_i);
// Apply "blk" to all the weak roots of the system. These include
// JNI weak roots, the code cache, system dictionary, symbol table,
// string table, and referents of reachable weak refs.
void g1_process_weak_roots(OopClosure* root_closure,
OopClosure* non_root_closure);
// Invoke "save_marks" on all heap regions.
void save_marks();
// Free a heap region.
void free_region(HeapRegion* hr);
// A component of "free_region", exposed for 'batching'.
// All the params after "hr" are out params: the used bytes of the freed
// region(s), the number of H regions cleared, the number of regions
// freed, and pointers to the head and tail of a list of freed contig
// regions, linked throught the "next_on_unclean_list" field.
void free_region_work(HeapRegion* hr,
size_t& pre_used,
size_t& cleared_h,
size_t& freed_regions,
UncleanRegionList* list,
bool par = false);
// The concurrent marker (and the thread it runs in.)
ConcurrentMark* _cm;
ConcurrentMarkThread* _cmThread;
bool _mark_in_progress;
// The concurrent refiner.
ConcurrentG1Refine* _cg1r;
// The concurrent zero-fill thread.
ConcurrentZFThread* _czft;
// The parallel task queues
RefToScanQueueSet *_task_queues;
// True iff a evacuation has failed in the current collection.
bool _evacuation_failed;
// Set the attribute indicating whether evacuation has failed in the
// current collection.
void set_evacuation_failed(bool b) { _evacuation_failed = b; }
// Failed evacuations cause some logical from-space objects to have
// forwarding pointers to themselves. Reset them.
void remove_self_forwarding_pointers();
// When one is non-null, so is the other. Together, they each pair is
// an object with a preserved mark, and its mark value.
GrowableArray<oop>* _objs_with_preserved_marks;
GrowableArray<markOop>* _preserved_marks_of_objs;
// Preserve the mark of "obj", if necessary, in preparation for its mark
// word being overwritten with a self-forwarding-pointer.
void preserve_mark_if_necessary(oop obj, markOop m);
// The stack of evac-failure objects left to be scanned.
GrowableArray<oop>* _evac_failure_scan_stack;
// The closure to apply to evac-failure objects.
OopsInHeapRegionClosure* _evac_failure_closure;
// Set the field above.
void
set_evac_failure_closure(OopsInHeapRegionClosure* evac_failure_closure) {
_evac_failure_closure = evac_failure_closure;
}
// Push "obj" on the scan stack.
void push_on_evac_failure_scan_stack(oop obj);
// Process scan stack entries until the stack is empty.
void drain_evac_failure_scan_stack();
// True iff an invocation of "drain_scan_stack" is in progress; to
// prevent unnecessary recursion.
bool _drain_in_progress;
// Do any necessary initialization for evacuation-failure handling.
// "cl" is the closure that will be used to process evac-failure
// objects.
void init_for_evac_failure(OopsInHeapRegionClosure* cl);
// Do any necessary cleanup for evacuation-failure handling data
// structures.
void finalize_for_evac_failure();
// An attempt to evacuate "obj" has failed; take necessary steps.
oop handle_evacuation_failure_par(OopsInHeapRegionClosure* cl, oop obj);
void handle_evacuation_failure_common(oop obj, markOop m);
// Ensure that the relevant gc_alloc regions are set.
void get_gc_alloc_regions();
// We're done with GC alloc regions. We are going to tear down the
// gc alloc list and remove the gc alloc tag from all the regions on
// that list. However, we will also retain the last (i.e., the one
// that is half-full) GC alloc region, per GCAllocPurpose, for
// possible reuse during the next collection, provided
// _retain_gc_alloc_region[] indicates that it should be the
// case. Said regions are kept in the _retained_gc_alloc_regions[]
// array. If the parameter totally is set, we will not retain any
// regions, irrespective of what _retain_gc_alloc_region[]
// indicates.
void release_gc_alloc_regions(bool totally);
#ifndef PRODUCT
// Useful for debugging.
void print_gc_alloc_regions();
#endif // !PRODUCT
// Instance of the concurrent mark is_alive closure for embedding
// into the reference processor as the is_alive_non_header. This
// prevents unnecessary additions to the discovered lists during
// concurrent discovery.
G1CMIsAliveClosure _is_alive_closure;
// ("Weak") Reference processing support
ReferenceProcessor* _ref_processor;
enum G1H_process_strong_roots_tasks {
G1H_PS_mark_stack_oops_do,
G1H_PS_refProcessor_oops_do,
// Leave this one last.
G1H_PS_NumElements
};
SubTasksDone* _process_strong_tasks;
// List of regions which require zero filling.
UncleanRegionList _unclean_region_list;
bool _unclean_regions_coming;
public:
SubTasksDone* process_strong_tasks() { return _process_strong_tasks; }
void set_refine_cte_cl_concurrency(bool concurrent);
RefToScanQueue *task_queue(int i) const;
// A set of cards where updates happened during the GC
DirtyCardQueueSet& dirty_card_queue_set() { return _dirty_card_queue_set; }
// A DirtyCardQueueSet that is used to hold cards that contain
// references into the current collection set. This is used to
// update the remembered sets of the regions in the collection
// set in the event of an evacuation failure.
DirtyCardQueueSet& into_cset_dirty_card_queue_set()
{ return _into_cset_dirty_card_queue_set; }
// Create a G1CollectedHeap with the specified policy.
// Must call the initialize method afterwards.
// May not return if something goes wrong.
G1CollectedHeap(G1CollectorPolicy* policy);
// Initialize the G1CollectedHeap to have the initial and
// maximum sizes, permanent generation, and remembered and barrier sets
// specified by the policy object.
jint initialize();
virtual void ref_processing_init();
void set_par_threads(int t) {
SharedHeap::set_par_threads(t);
_process_strong_tasks->set_n_threads(t);
}
virtual CollectedHeap::Name kind() const {
return CollectedHeap::G1CollectedHeap;
}
// The current policy object for the collector.
G1CollectorPolicy* g1_policy() const { return _g1_policy; }
// Adaptive size policy. No such thing for g1.
virtual AdaptiveSizePolicy* size_policy() { return NULL; }
// The rem set and barrier set.
G1RemSet* g1_rem_set() const { return _g1_rem_set; }
ModRefBarrierSet* mr_bs() const { return _mr_bs; }
// The rem set iterator.
HeapRegionRemSetIterator* rem_set_iterator(int i) {
return _rem_set_iterator[i];
}
HeapRegionRemSetIterator* rem_set_iterator() {
return _rem_set_iterator[0];
}
unsigned get_gc_time_stamp() {
return _gc_time_stamp;
}
void reset_gc_time_stamp() {
_gc_time_stamp = 0;
OrderAccess::fence();
}
void increment_gc_time_stamp() {
++_gc_time_stamp;
OrderAccess::fence();
}
void iterate_dirty_card_closure(CardTableEntryClosure* cl,
DirtyCardQueue* into_cset_dcq,
bool concurrent, int worker_i);
// The shared block offset table array.
G1BlockOffsetSharedArray* bot_shared() const { return _bot_shared; }
// Reference Processing accessor
ReferenceProcessor* ref_processor() { return _ref_processor; }
// Reserved (g1 only; super method includes perm), capacity and the used
// portion in bytes.
size_t g1_reserved_obj_bytes() const { return _g1_reserved.byte_size(); }
virtual size_t capacity() const;
virtual size_t used() const;
// This should be called when we're not holding the heap lock. The
// result might be a bit inaccurate.
size_t used_unlocked() const;
size_t recalculate_used() const;
#ifndef PRODUCT
size_t recalculate_used_regions() const;
#endif // PRODUCT
// These virtual functions do the actual allocation.
// Some heaps may offer a contiguous region for shared non-blocking
// allocation, via inlined code (by exporting the address of the top and
// end fields defining the extent of the contiguous allocation region.)
// But G1CollectedHeap doesn't yet support this.
// Return an estimate of the maximum allocation that could be performed
// without triggering any collection or expansion activity. In a
// generational collector, for example, this is probably the largest
// allocation that could be supported (without expansion) in the youngest
// generation. It is "unsafe" because no locks are taken; the result
// should be treated as an approximation, not a guarantee, for use in
// heuristic resizing decisions.
virtual size_t unsafe_max_alloc();
virtual bool is_maximal_no_gc() const {
return _g1_storage.uncommitted_size() == 0;
}
// The total number of regions in the heap.
size_t n_regions();
// The number of regions that are completely free.
size_t max_regions();
// The number of regions that are completely free.
size_t free_regions();
// The number of regions that are not completely free.
size_t used_regions() { return n_regions() - free_regions(); }
// True iff the ZF thread should run.
bool should_zf();
// The number of regions available for "regular" expansion.
size_t expansion_regions() { return _expansion_regions; }
#ifndef PRODUCT
bool regions_accounted_for();
bool print_region_accounting_info();
void print_region_counts();
#endif
HeapRegion* alloc_region_from_unclean_list(bool zero_filled);
HeapRegion* alloc_region_from_unclean_list_locked(bool zero_filled);
void put_region_on_unclean_list(HeapRegion* r);
void put_region_on_unclean_list_locked(HeapRegion* r);
void prepend_region_list_on_unclean_list(UncleanRegionList* list);
void prepend_region_list_on_unclean_list_locked(UncleanRegionList* list);
void set_unclean_regions_coming(bool b);
void set_unclean_regions_coming_locked(bool b);
// Wait for cleanup to be complete.
void wait_for_cleanup_complete();
// Like above, but assumes that the calling thread owns the Heap_lock.
void wait_for_cleanup_complete_locked();
// Return the head of the unclean list.
HeapRegion* peek_unclean_region_list_locked();
// Remove and return the head of the unclean list.
HeapRegion* pop_unclean_region_list_locked();
// List of regions which are zero filled and ready for allocation.
HeapRegion* _free_region_list;
// Number of elements on the free list.
size_t _free_region_list_size;
// If the head of the unclean list is ZeroFilled, move it to the free
// list.
bool move_cleaned_region_to_free_list_locked();
bool move_cleaned_region_to_free_list();
void put_free_region_on_list_locked(HeapRegion* r);
void put_free_region_on_list(HeapRegion* r);
// Remove and return the head element of the free list.
HeapRegion* pop_free_region_list_locked();
// If "zero_filled" is true, we first try the free list, then we try the
// unclean list, zero-filling the result. If "zero_filled" is false, we
// first try the unclean list, then the zero-filled list.
HeapRegion* alloc_free_region_from_lists(bool zero_filled);
// Verify the integrity of the region lists.
void remove_allocated_regions_from_lists();
bool verify_region_lists();
bool verify_region_lists_locked();
size_t unclean_region_list_length();
size_t free_region_list_length();
// Perform a collection of the heap; intended for use in implementing
// "System.gc". This probably implies as full a collection as the
// "CollectedHeap" supports.
virtual void collect(GCCause::Cause cause);
// The same as above but assume that the caller holds the Heap_lock.
void collect_locked(GCCause::Cause cause);
// This interface assumes that it's being called by the
// vm thread. It collects the heap assuming that the
// heap lock is already held and that we are executing in
// the context of the vm thread.
virtual void collect_as_vm_thread(GCCause::Cause cause);
// True iff a evacuation has failed in the most-recent collection.
bool evacuation_failed() { return _evacuation_failed; }
// Free a region if it is totally full of garbage. Returns the number of
// bytes freed (0 ==> didn't free it).
size_t free_region_if_totally_empty(HeapRegion *hr);
void free_region_if_totally_empty_work(HeapRegion *hr,
size_t& pre_used,
size_t& cleared_h_regions,
size_t& freed_regions,
UncleanRegionList* list,
bool par = false);
// If we've done free region work that yields the given changes, update
// the relevant global variables.
void finish_free_region_work(size_t pre_used,
size_t cleared_h_regions,
size_t freed_regions,
UncleanRegionList* list);
// Returns "TRUE" iff "p" points into the allocated area of the heap.
virtual bool is_in(const void* p) const;
// Return "TRUE" iff the given object address is within the collection
// set.
inline bool obj_in_cs(oop obj);
// Return "TRUE" iff the given object address is in the reserved
// region of g1 (excluding the permanent generation).
bool is_in_g1_reserved(const void* p) const {
return _g1_reserved.contains(p);
}
// Returns a MemRegion that corresponds to the space that has been
// committed in the heap
MemRegion g1_committed() {
return _g1_committed;
}
NOT_PRODUCT(bool is_in_closed_subset(const void* p) const;)
// Dirty card table entries covering a list of young regions.
void dirtyCardsForYoungRegions(CardTableModRefBS* ct_bs, HeapRegion* list);
// This resets the card table to all zeros. It is used after
// a collection pause which used the card table to claim cards.
void cleanUpCardTable();
// Iteration functions.
// Iterate over all the ref-containing fields of all objects, calling
// "cl.do_oop" on each.
virtual void oop_iterate(OopClosure* cl) {
oop_iterate(cl, true);
}
void oop_iterate(OopClosure* cl, bool do_perm);
// Same as above, restricted to a memory region.
virtual void oop_iterate(MemRegion mr, OopClosure* cl) {
oop_iterate(mr, cl, true);
}
void oop_iterate(MemRegion mr, OopClosure* cl, bool do_perm);
// Iterate over all objects, calling "cl.do_object" on each.
virtual void object_iterate(ObjectClosure* cl) {
object_iterate(cl, true);
}
virtual void safe_object_iterate(ObjectClosure* cl) {
object_iterate(cl, true);
}
void object_iterate(ObjectClosure* cl, bool do_perm);
// Iterate over all objects allocated since the last collection, calling
// "cl.do_object" on each. The heap must have been initialized properly
// to support this function, or else this call will fail.
virtual void object_iterate_since_last_GC(ObjectClosure* cl);
// Iterate over all spaces in use in the heap, in ascending address order.
virtual void space_iterate(SpaceClosure* cl);
// Iterate over heap regions, in address order, terminating the
// iteration early if the "doHeapRegion" method returns "true".
void heap_region_iterate(HeapRegionClosure* blk);
// Iterate over heap regions starting with r (or the first region if "r"
// is NULL), in address order, terminating early if the "doHeapRegion"
// method returns "true".
void heap_region_iterate_from(HeapRegion* r, HeapRegionClosure* blk);
// As above but starting from the region at index idx.
void heap_region_iterate_from(int idx, HeapRegionClosure* blk);
HeapRegion* region_at(size_t idx);
// Divide the heap region sequence into "chunks" of some size (the number
// of regions divided by the number of parallel threads times some
// overpartition factor, currently 4). Assumes that this will be called
// in parallel by ParallelGCThreads worker threads with discinct worker
// ids in the range [0..max(ParallelGCThreads-1, 1)], that all parallel
// calls will use the same "claim_value", and that that claim value is
// different from the claim_value of any heap region before the start of
// the iteration. Applies "blk->doHeapRegion" to each of the regions, by
// attempting to claim the first region in each chunk, and, if
// successful, applying the closure to each region in the chunk (and
// setting the claim value of the second and subsequent regions of the
// chunk.) For now requires that "doHeapRegion" always returns "false",
// i.e., that a closure never attempt to abort a traversal.
void heap_region_par_iterate_chunked(HeapRegionClosure* blk,
int worker,
jint claim_value);
// It resets all the region claim values to the default.
void reset_heap_region_claim_values();
#ifdef ASSERT
bool check_heap_region_claim_values(jint claim_value);
#endif // ASSERT
// Iterate over the regions (if any) in the current collection set.
void collection_set_iterate(HeapRegionClosure* blk);
// As above but starting from region r
void collection_set_iterate_from(HeapRegion* r, HeapRegionClosure *blk);
// Returns the first (lowest address) compactible space in the heap.
virtual CompactibleSpace* first_compactible_space();
// A CollectedHeap will contain some number of spaces. This finds the
// space containing a given address, or else returns NULL.
virtual Space* space_containing(const void* addr) const;
// A G1CollectedHeap will contain some number of heap regions. This
// finds the region containing a given address, or else returns NULL.
HeapRegion* heap_region_containing(const void* addr) const;
// Like the above, but requires "addr" to be in the heap (to avoid a
// null-check), and unlike the above, may return an continuing humongous
// region.
HeapRegion* heap_region_containing_raw(const void* addr) const;
// A CollectedHeap is divided into a dense sequence of "blocks"; that is,
// each address in the (reserved) heap is a member of exactly
// one block. The defining characteristic of a block is that it is
// possible to find its size, and thus to progress forward to the next
// block. (Blocks may be of different sizes.) Thus, blocks may
// represent Java objects, or they might be free blocks in a
// free-list-based heap (or subheap), as long as the two kinds are
// distinguishable and the size of each is determinable.
// Returns the address of the start of the "block" that contains the
// address "addr". We say "blocks" instead of "object" since some heaps
// may not pack objects densely; a chunk may either be an object or a
// non-object.
virtual HeapWord* block_start(const void* addr) const;
// Requires "addr" to be the start of a chunk, and returns its size.
// "addr + size" is required to be the start of a new chunk, or the end
// of the active area of the heap.
virtual size_t block_size(const HeapWord* addr) const;
// Requires "addr" to be the start of a block, and returns "TRUE" iff
// the block is an object.
virtual bool block_is_obj(const HeapWord* addr) const;
// Does this heap support heap inspection? (+PrintClassHistogram)
virtual bool supports_heap_inspection() const { return true; }
// Section on thread-local allocation buffers (TLABs)
// See CollectedHeap for semantics.
virtual bool supports_tlab_allocation() const;
virtual size_t tlab_capacity(Thread* thr) const;
virtual size_t unsafe_max_tlab_alloc(Thread* thr) const;
// Can a compiler initialize a new object without store barriers?
// This permission only extends from the creation of a new object
// via a TLAB up to the first subsequent safepoint. If such permission
// is granted for this heap type, the compiler promises to call
// defer_store_barrier() below on any slow path allocation of
// a new object for which such initializing store barriers will
// have been elided. G1, like CMS, allows this, but should be
// ready to provide a compensating write barrier as necessary
// if that storage came out of a non-young region. The efficiency
// of this implementation depends crucially on being able to
// answer very efficiently in constant time whether a piece of
// storage in the heap comes from a young region or not.
// See ReduceInitialCardMarks.
virtual bool can_elide_tlab_store_barriers() const {
// 6920090: Temporarily disabled, because of lingering
// instabilities related to RICM with G1. In the
// interim, the option ReduceInitialCardMarksForG1
// below is left solely as a debugging device at least
// until 6920109 fixes the instabilities.
return ReduceInitialCardMarksForG1;
}
virtual bool card_mark_must_follow_store() const {
return true;
}
bool is_in_young(oop obj) {
HeapRegion* hr = heap_region_containing(obj);
return hr != NULL && hr->is_young();
}
// We don't need barriers for initializing stores to objects
// in the young gen: for the SATB pre-barrier, there is no
// pre-value that needs to be remembered; for the remembered-set
// update logging post-barrier, we don't maintain remembered set
// information for young gen objects. Note that non-generational
// G1 does not have any "young" objects, should not elide
// the rs logging barrier and so should always answer false below.
// However, non-generational G1 (-XX:-G1Gen) appears to have
// bit-rotted so was not tested below.
virtual bool can_elide_initializing_store_barrier(oop new_obj) {
// Re 6920090, 6920109 above.
assert(ReduceInitialCardMarksForG1, "Else cannot be here");
assert(G1Gen || !is_in_young(new_obj),
"Non-generational G1 should never return true below");
return is_in_young(new_obj);
}
// Can a compiler elide a store barrier when it writes
// a permanent oop into the heap? Applies when the compiler
// is storing x to the heap, where x->is_perm() is true.
virtual bool can_elide_permanent_oop_store_barriers() const {
// At least until perm gen collection is also G1-ified, at
// which point this should return false.
return true;
}
virtual bool allocs_are_zero_filled();
// The boundary between a "large" and "small" array of primitives, in
// words.
virtual size_t large_typearray_limit();
// Returns "true" iff the given word_size is "very large".
static bool isHumongous(size_t word_size) {
// Note this has to be strictly greater-than as the TLABs
// are capped at the humongous thresold and we want to
// ensure that we don't try to allocate a TLAB as
// humongous and that we don't allocate a humongous
// object in a TLAB.
return word_size > _humongous_object_threshold_in_words;
}
// Update mod union table with the set of dirty cards.
void updateModUnion();
// Set the mod union bits corresponding to the given memRegion. Note
// that this is always a safe operation, since it doesn't clear any
// bits.
void markModUnionRange(MemRegion mr);
// Records the fact that a marking phase is no longer in progress.
void set_marking_complete() {
_mark_in_progress = false;
}
void set_marking_started() {
_mark_in_progress = true;
}
bool mark_in_progress() {
return _mark_in_progress;
}
// Print the maximum heap capacity.
virtual size_t max_capacity() const;
virtual jlong millis_since_last_gc();
// Perform any cleanup actions necessary before allowing a verification.
virtual void prepare_for_verify();
// Perform verification.
// use_prev_marking == true -> use "prev" marking information,
// use_prev_marking == false -> use "next" marking information
// NOTE: Only the "prev" marking information is guaranteed to be
// consistent most of the time, so most calls to this should use
// use_prev_marking == true. Currently, there is only one case where
// this is called with use_prev_marking == false, which is to verify
// the "next" marking information at the end of remark.
void verify(bool allow_dirty, bool silent, bool use_prev_marking);
// Override; it uses the "prev" marking information
virtual void verify(bool allow_dirty, bool silent);
// Default behavior by calling print(tty);
virtual void print() const;
// This calls print_on(st, PrintHeapAtGCExtended).
virtual void print_on(outputStream* st) const;
// If extended is true, it will print out information for all
// regions in the heap by calling print_on_extended(st).
virtual void print_on(outputStream* st, bool extended) const;
virtual void print_on_extended(outputStream* st) const;
virtual void print_gc_threads_on(outputStream* st) const;
virtual void gc_threads_do(ThreadClosure* tc) const;
// Override
void print_tracing_info() const;
// If "addr" is a pointer into the (reserved?) heap, returns a positive
// number indicating the "arena" within the heap in which "addr" falls.
// Or else returns 0.
virtual int addr_to_arena_id(void* addr) const;
// Convenience function to be used in situations where the heap type can be
// asserted to be this type.
static G1CollectedHeap* heap();
void empty_young_list();
void set_region_short_lived_locked(HeapRegion* hr);
// add appropriate methods for any other surv rate groups
YoungList* young_list() { return _young_list; }
// debugging
bool check_young_list_well_formed() {
return _young_list->check_list_well_formed();
}
bool check_young_list_empty(bool check_heap,
bool check_sample = true);
// *** Stuff related to concurrent marking. It's not clear to me that so
// many of these need to be public.
// The functions below are helper functions that a subclass of
// "CollectedHeap" can use in the implementation of its virtual
// functions.
// This performs a concurrent marking of the live objects in a
// bitmap off to the side.
void doConcurrentMark();
// This is called from the marksweep collector which then does
// a concurrent mark and verifies that the results agree with
// the stop the world marking.
void checkConcurrentMark();
void do_sync_mark();
bool isMarkedPrev(oop obj) const;
bool isMarkedNext(oop obj) const;
// use_prev_marking == true -> use "prev" marking information,
// use_prev_marking == false -> use "next" marking information
bool is_obj_dead_cond(const oop obj,
const HeapRegion* hr,
const bool use_prev_marking) const {
if (use_prev_marking) {
return is_obj_dead(obj, hr);
} else {
return is_obj_ill(obj, hr);
}
}
// Determine if an object is dead, given the object and also
// the region to which the object belongs. An object is dead
// iff a) it was not allocated since the last mark and b) it
// is not marked.
bool is_obj_dead(const oop obj, const HeapRegion* hr) const {
return
!hr->obj_allocated_since_prev_marking(obj) &&
!isMarkedPrev(obj);
}
// This is used when copying an object to survivor space.
// If the object is marked live, then we mark the copy live.
// If the object is allocated since the start of this mark
// cycle, then we mark the copy live.
// If the object has been around since the previous mark
// phase, and hasn't been marked yet during this phase,
// then we don't mark it, we just wait for the
// current marking cycle to get to it.
// This function returns true when an object has been
// around since the previous marking and hasn't yet
// been marked during this marking.
bool is_obj_ill(const oop obj, const HeapRegion* hr) const {
return
!hr->obj_allocated_since_next_marking(obj) &&
!isMarkedNext(obj);
}
// Determine if an object is dead, given only the object itself.
// This will find the region to which the object belongs and
// then call the region version of the same function.
// Added if it is in permanent gen it isn't dead.
// Added if it is NULL it isn't dead.
// use_prev_marking == true -> use "prev" marking information,
// use_prev_marking == false -> use "next" marking information
bool is_obj_dead_cond(const oop obj,
const bool use_prev_marking) {
if (use_prev_marking) {
return is_obj_dead(obj);
} else {
return is_obj_ill(obj);
}
}
bool is_obj_dead(const oop obj) {
const HeapRegion* hr = heap_region_containing(obj);
if (hr == NULL) {
if (Universe::heap()->is_in_permanent(obj))
return false;
else if (obj == NULL) return false;
else return true;
}
else return is_obj_dead(obj, hr);
}
bool is_obj_ill(const oop obj) {
const HeapRegion* hr = heap_region_containing(obj);
if (hr == NULL) {
if (Universe::heap()->is_in_permanent(obj))
return false;
else if (obj == NULL) return false;
else return true;
}
else return is_obj_ill(obj, hr);
}
// The following is just to alert the verification code
// that a full collection has occurred and that the
// remembered sets are no longer up to date.
bool _full_collection;
void set_full_collection() { _full_collection = true;}
void clear_full_collection() {_full_collection = false;}
bool full_collection() {return _full_collection;}
ConcurrentMark* concurrent_mark() const { return _cm; }
ConcurrentG1Refine* concurrent_g1_refine() const { return _cg1r; }
// The dirty cards region list is used to record a subset of regions
// whose cards need clearing. The list if populated during the
// remembered set scanning and drained during the card table
// cleanup. Although the methods are reentrant, population/draining
// phases must not overlap. For synchronization purposes the last
// element on the list points to itself.
HeapRegion* _dirty_cards_region_list;
void push_dirty_cards_region(HeapRegion* hr);
HeapRegion* pop_dirty_cards_region();
public:
void stop_conc_gc_threads();
// <NEW PREDICTION>
double predict_region_elapsed_time_ms(HeapRegion* hr, bool young);
void check_if_region_is_too_expensive(double predicted_time_ms);
size_t pending_card_num();
size_t max_pending_card_num();
size_t cards_scanned();
// </NEW PREDICTION>
protected:
size_t _max_heap_capacity;
public:
// Temporary: call to mark things unimplemented for the G1 heap (e.g.,
// MemoryService). In productization, we can make this assert false
// to catch such places (as well as searching for calls to this...)
static void g1_unimplemented();
};
#define use_local_bitmaps 1
#define verify_local_bitmaps 0
#define oop_buffer_length 256
#ifndef PRODUCT
class GCLabBitMap;
class GCLabBitMapClosure: public BitMapClosure {
private:
ConcurrentMark* _cm;
GCLabBitMap* _bitmap;
public:
GCLabBitMapClosure(ConcurrentMark* cm,
GCLabBitMap* bitmap) {
_cm = cm;
_bitmap = bitmap;
}
virtual bool do_bit(size_t offset);
};
#endif // !PRODUCT
class GCLabBitMap: public BitMap {
private:
ConcurrentMark* _cm;
int _shifter;
size_t _bitmap_word_covers_words;
// beginning of the heap
HeapWord* _heap_start;
// this is the actual start of the GCLab
HeapWord* _real_start_word;
// this is the actual end of the GCLab
HeapWord* _real_end_word;
// this is the first word, possibly located before the actual start
// of the GCLab, that corresponds to the first bit of the bitmap
HeapWord* _start_word;
// size of a GCLab in words
size_t _gclab_word_size;
static int shifter() {
return MinObjAlignment - 1;
}
// how many heap words does a single bitmap word corresponds to?
static size_t bitmap_word_covers_words() {
return BitsPerWord << shifter();
}
size_t gclab_word_size() const {
return _gclab_word_size;
}
// Calculates actual GCLab size in words
size_t gclab_real_word_size() const {
return bitmap_size_in_bits(pointer_delta(_real_end_word, _start_word))
/ BitsPerWord;
}
static size_t bitmap_size_in_bits(size_t gclab_word_size) {
size_t bits_in_bitmap = gclab_word_size >> shifter();
// We are going to ensure that the beginning of a word in this
// bitmap also corresponds to the beginning of a word in the
// global marking bitmap. To handle the case where a GCLab
// starts from the middle of the bitmap, we need to add enough
// space (i.e. up to a bitmap word) to ensure that we have
// enough bits in the bitmap.
return bits_in_bitmap + BitsPerWord - 1;
}
public:
GCLabBitMap(HeapWord* heap_start, size_t gclab_word_size)
: BitMap(bitmap_size_in_bits(gclab_word_size)),
_cm(G1CollectedHeap::heap()->concurrent_mark()),
_shifter(shifter()),
_bitmap_word_covers_words(bitmap_word_covers_words()),
_heap_start(heap_start),
_gclab_word_size(gclab_word_size),
_real_start_word(NULL),
_real_end_word(NULL),
_start_word(NULL)
{
guarantee( size_in_words() >= bitmap_size_in_words(),
"just making sure");
}
inline unsigned heapWordToOffset(HeapWord* addr) {
unsigned offset = (unsigned) pointer_delta(addr, _start_word) >> _shifter;
assert(offset < size(), "offset should be within bounds");
return offset;
}
inline HeapWord* offsetToHeapWord(size_t offset) {
HeapWord* addr = _start_word + (offset << _shifter);
assert(_real_start_word <= addr && addr < _real_end_word, "invariant");
return addr;
}
bool fields_well_formed() {
bool ret1 = (_real_start_word == NULL) &&
(_real_end_word == NULL) &&
(_start_word == NULL);
if (ret1)
return true;
bool ret2 = _real_start_word >= _start_word &&
_start_word < _real_end_word &&
(_real_start_word + _gclab_word_size) == _real_end_word &&
(_start_word + _gclab_word_size + _bitmap_word_covers_words)
> _real_end_word;
return ret2;
}
inline bool mark(HeapWord* addr) {
guarantee(use_local_bitmaps, "invariant");
assert(fields_well_formed(), "invariant");
if (addr >= _real_start_word && addr < _real_end_word) {
assert(!isMarked(addr), "should not have already been marked");
// first mark it on the bitmap
at_put(heapWordToOffset(addr), true);
return true;
} else {
return false;
}
}
inline bool isMarked(HeapWord* addr) {
guarantee(use_local_bitmaps, "invariant");
assert(fields_well_formed(), "invariant");
return at(heapWordToOffset(addr));
}
void set_buffer(HeapWord* start) {
guarantee(use_local_bitmaps, "invariant");
clear();
assert(start != NULL, "invariant");
_real_start_word = start;
_real_end_word = start + _gclab_word_size;
size_t diff =
pointer_delta(start, _heap_start) % _bitmap_word_covers_words;
_start_word = start - diff;
assert(fields_well_formed(), "invariant");
}
#ifndef PRODUCT
void verify() {
// verify that the marks have been propagated
GCLabBitMapClosure cl(_cm, this);
iterate(&cl);
}
#endif // PRODUCT
void retire() {
guarantee(use_local_bitmaps, "invariant");
assert(fields_well_formed(), "invariant");
if (_start_word != NULL) {
CMBitMap* mark_bitmap = _cm->nextMarkBitMap();
// this means that the bitmap was set up for the GCLab
assert(_real_start_word != NULL && _real_end_word != NULL, "invariant");
mark_bitmap->mostly_disjoint_range_union(this,
0, // always start from the start of the bitmap
_start_word,
gclab_real_word_size());
_cm->grayRegionIfNecessary(MemRegion(_real_start_word, _real_end_word));
#ifndef PRODUCT
if (use_local_bitmaps && verify_local_bitmaps)
verify();
#endif // PRODUCT
} else {
assert(_real_start_word == NULL && _real_end_word == NULL, "invariant");
}
}
size_t bitmap_size_in_words() const {
return (bitmap_size_in_bits(gclab_word_size()) + BitsPerWord - 1) / BitsPerWord;
}
};
class G1ParGCAllocBuffer: public ParGCAllocBuffer {
private:
bool _retired;
bool _during_marking;
GCLabBitMap _bitmap;
public:
G1ParGCAllocBuffer(size_t gclab_word_size) :
ParGCAllocBuffer(gclab_word_size),
_during_marking(G1CollectedHeap::heap()->mark_in_progress()),
_bitmap(G1CollectedHeap::heap()->reserved_region().start(), gclab_word_size),
_retired(false)
{ }
inline bool mark(HeapWord* addr) {
guarantee(use_local_bitmaps, "invariant");
assert(_during_marking, "invariant");
return _bitmap.mark(addr);
}
inline void set_buf(HeapWord* buf) {
if (use_local_bitmaps && _during_marking)
_bitmap.set_buffer(buf);
ParGCAllocBuffer::set_buf(buf);
_retired = false;
}
inline void retire(bool end_of_gc, bool retain) {
if (_retired)
return;
if (use_local_bitmaps && _during_marking) {
_bitmap.retire();
}
ParGCAllocBuffer::retire(end_of_gc, retain);
_retired = true;
}
};
class G1ParScanThreadState : public StackObj {
protected:
G1CollectedHeap* _g1h;
RefToScanQueue* _refs;
DirtyCardQueue _dcq;
CardTableModRefBS* _ct_bs;
G1RemSet* _g1_rem;
G1ParGCAllocBuffer _surviving_alloc_buffer;
G1ParGCAllocBuffer _tenured_alloc_buffer;
G1ParGCAllocBuffer* _alloc_buffers[GCAllocPurposeCount];
ageTable _age_table;
size_t _alloc_buffer_waste;
size_t _undo_waste;
OopsInHeapRegionClosure* _evac_failure_cl;
G1ParScanHeapEvacClosure* _evac_cl;
G1ParScanPartialArrayClosure* _partial_scan_cl;
int _hash_seed;
int _queue_num;
size_t _term_attempts;
double _start;
double _start_strong_roots;
double _strong_roots_time;
double _start_term;
double _term_time;
// Map from young-age-index (0 == not young, 1 is youngest) to
// surviving words. base is what we get back from the malloc call
size_t* _surviving_young_words_base;
// this points into the array, as we use the first few entries for padding
size_t* _surviving_young_words;
#define PADDING_ELEM_NUM (DEFAULT_CACHE_LINE_SIZE / sizeof(size_t))
void add_to_alloc_buffer_waste(size_t waste) { _alloc_buffer_waste += waste; }
void add_to_undo_waste(size_t waste) { _undo_waste += waste; }
DirtyCardQueue& dirty_card_queue() { return _dcq; }
CardTableModRefBS* ctbs() { return _ct_bs; }
template <class T> void immediate_rs_update(HeapRegion* from, T* p, int tid) {
if (!from->is_survivor()) {
_g1_rem->par_write_ref(from, p, tid);
}
}
template <class T> void deferred_rs_update(HeapRegion* from, T* p, int tid) {
// If the new value of the field points to the same region or
// is the to-space, we don't need to include it in the Rset updates.
if (!from->is_in_reserved(oopDesc::load_decode_heap_oop(p)) && !from->is_survivor()) {
size_t card_index = ctbs()->index_for(p);
// If the card hasn't been added to the buffer, do it.
if (ctbs()->mark_card_deferred(card_index)) {
dirty_card_queue().enqueue((jbyte*)ctbs()->byte_for_index(card_index));
}
}
}
public:
G1ParScanThreadState(G1CollectedHeap* g1h, int queue_num);
~G1ParScanThreadState() {
FREE_C_HEAP_ARRAY(size_t, _surviving_young_words_base);
}
RefToScanQueue* refs() { return _refs; }
ageTable* age_table() { return &_age_table; }
G1ParGCAllocBuffer* alloc_buffer(GCAllocPurpose purpose) {
return _alloc_buffers[purpose];
}
size_t alloc_buffer_waste() const { return _alloc_buffer_waste; }
size_t undo_waste() const { return _undo_waste; }
#ifdef ASSERT
bool verify_ref(narrowOop* ref) const;
bool verify_ref(oop* ref) const;
bool verify_task(StarTask ref) const;
#endif // ASSERT
template <class T> void push_on_queue(T* ref) {
assert(verify_ref(ref), "sanity");
refs()->push(ref);
}
template <class T> void update_rs(HeapRegion* from, T* p, int tid) {
if (G1DeferredRSUpdate) {
deferred_rs_update(from, p, tid);
} else {
immediate_rs_update(from, p, tid);
}
}
HeapWord* allocate_slow(GCAllocPurpose purpose, size_t word_sz) {
HeapWord* obj = NULL;
size_t gclab_word_size = _g1h->desired_plab_sz(purpose);
if (word_sz * 100 < gclab_word_size * ParallelGCBufferWastePct) {
G1ParGCAllocBuffer* alloc_buf = alloc_buffer(purpose);
assert(gclab_word_size == alloc_buf->word_sz(),
"dynamic resizing is not supported");
add_to_alloc_buffer_waste(alloc_buf->words_remaining());
alloc_buf->retire(false, false);
HeapWord* buf = _g1h->par_allocate_during_gc(purpose, gclab_word_size);
if (buf == NULL) return NULL; // Let caller handle allocation failure.
// Otherwise.
alloc_buf->set_buf(buf);
obj = alloc_buf->allocate(word_sz);
assert(obj != NULL, "buffer was definitely big enough...");
} else {
obj = _g1h->par_allocate_during_gc(purpose, word_sz);
}
return obj;
}
HeapWord* allocate(GCAllocPurpose purpose, size_t word_sz) {
HeapWord* obj = alloc_buffer(purpose)->allocate(word_sz);
if (obj != NULL) return obj;
return allocate_slow(purpose, word_sz);
}
void undo_allocation(GCAllocPurpose purpose, HeapWord* obj, size_t word_sz) {
if (alloc_buffer(purpose)->contains(obj)) {
assert(alloc_buffer(purpose)->contains(obj + word_sz - 1),
"should contain whole object");
alloc_buffer(purpose)->undo_allocation(obj, word_sz);
} else {
CollectedHeap::fill_with_object(obj, word_sz);
add_to_undo_waste(word_sz);
}
}
void set_evac_failure_closure(OopsInHeapRegionClosure* evac_failure_cl) {
_evac_failure_cl = evac_failure_cl;
}
OopsInHeapRegionClosure* evac_failure_closure() {
return _evac_failure_cl;
}
void set_evac_closure(G1ParScanHeapEvacClosure* evac_cl) {
_evac_cl = evac_cl;
}
void set_partial_scan_closure(G1ParScanPartialArrayClosure* partial_scan_cl) {
_partial_scan_cl = partial_scan_cl;
}
int* hash_seed() { return &_hash_seed; }
int queue_num() { return _queue_num; }
size_t term_attempts() const { return _term_attempts; }
void note_term_attempt() { _term_attempts++; }
void start_strong_roots() {
_start_strong_roots = os::elapsedTime();
}
void end_strong_roots() {
_strong_roots_time += (os::elapsedTime() - _start_strong_roots);
}
double strong_roots_time() const { return _strong_roots_time; }
void start_term_time() {
note_term_attempt();
_start_term = os::elapsedTime();
}
void end_term_time() {
_term_time += (os::elapsedTime() - _start_term);
}
double term_time() const { return _term_time; }
double elapsed_time() const {
return os::elapsedTime() - _start;
}
static void
print_termination_stats_hdr(outputStream* const st = gclog_or_tty);
void
print_termination_stats(int i, outputStream* const st = gclog_or_tty) const;
size_t* surviving_young_words() {
// We add on to hide entry 0 which accumulates surviving words for
// age -1 regions (i.e. non-young ones)
return _surviving_young_words;
}
void retire_alloc_buffers() {
for (int ap = 0; ap < GCAllocPurposeCount; ++ap) {
size_t waste = _alloc_buffers[ap]->words_remaining();
add_to_alloc_buffer_waste(waste);
_alloc_buffers[ap]->retire(true, false);
}
}
template <class T> void deal_with_reference(T* ref_to_scan) {
if (has_partial_array_mask(ref_to_scan)) {
_partial_scan_cl->do_oop_nv(ref_to_scan);
} else {
// Note: we can use "raw" versions of "region_containing" because
// "obj_to_scan" is definitely in the heap, and is not in a
// humongous region.
HeapRegion* r = _g1h->heap_region_containing_raw(ref_to_scan);
_evac_cl->set_region(r);
_evac_cl->do_oop_nv(ref_to_scan);
}
}
void deal_with_reference(StarTask ref) {
assert(verify_task(ref), "sanity");
if (ref.is_narrow()) {
deal_with_reference((narrowOop*)ref);
} else {
deal_with_reference((oop*)ref);
}
}
public:
void trim_queue();
};
#endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTEDHEAP_HPP