6819891: ParNew: Fix work queue overflow code to deal correctly with +UseCompressedOops
Summary: When using compressed oops, rather than chaining the overflowed grey objects' pre-images through their klass words, we use GC-worker thread-local overflow stacks.
Reviewed-by: jcoomes, jmasa
/*
* Copyright 2001-2009 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
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*
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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).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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# include "incls/_precompiled.incl"
# include "incls/_parNewGeneration.cpp.incl"
#ifdef _MSC_VER
#pragma warning( push )
#pragma warning( disable:4355 ) // 'this' : used in base member initializer list
#endif
ParScanThreadState::ParScanThreadState(Space* to_space_,
ParNewGeneration* gen_,
Generation* old_gen_,
int thread_num_,
ObjToScanQueueSet* work_queue_set_,
size_t desired_plab_sz_,
ParallelTaskTerminator& term_) :
_to_space(to_space_), _old_gen(old_gen_), _young_gen(gen_), _thread_num(thread_num_),
_work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false),
_ageTable(false), // false ==> not the global age table, no perf data.
_to_space_alloc_buffer(desired_plab_sz_),
_to_space_closure(gen_, this), _old_gen_closure(gen_, this),
_to_space_root_closure(gen_, this), _old_gen_root_closure(gen_, this),
_older_gen_closure(gen_, this),
_evacuate_followers(this, &_to_space_closure, &_old_gen_closure,
&_to_space_root_closure, gen_, &_old_gen_root_closure,
work_queue_set_, &term_),
_is_alive_closure(gen_), _scan_weak_ref_closure(gen_, this),
_keep_alive_closure(&_scan_weak_ref_closure),
_pushes(0), _pops(0), _steals(0), _steal_attempts(0), _term_attempts(0),
_strong_roots_time(0.0), _term_time(0.0)
{
_survivor_chunk_array =
(ChunkArray*) old_gen()->get_data_recorder(thread_num());
_hash_seed = 17; // Might want to take time-based random value.
_start = os::elapsedTime();
_old_gen_closure.set_generation(old_gen_);
_old_gen_root_closure.set_generation(old_gen_);
if (UseCompressedOops) {
_overflow_stack = new (ResourceObj::C_HEAP) GrowableArray<oop>(512, true);
} else {
_overflow_stack = NULL;
}
}
#ifdef _MSC_VER
#pragma warning( pop )
#endif
void ParScanThreadState::record_survivor_plab(HeapWord* plab_start,
size_t plab_word_size) {
ChunkArray* sca = survivor_chunk_array();
if (sca != NULL) {
// A non-null SCA implies that we want the PLAB data recorded.
sca->record_sample(plab_start, plab_word_size);
}
}
bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const {
return new_obj->is_objArray() &&
arrayOop(new_obj)->length() > ParGCArrayScanChunk &&
new_obj != old_obj;
}
void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {
assert(old->is_objArray(), "must be obj array");
assert(old->is_forwarded(), "must be forwarded");
assert(Universe::heap()->is_in_reserved(old), "must be in heap.");
assert(!old_gen()->is_in(old), "must be in young generation.");
objArrayOop obj = objArrayOop(old->forwardee());
// Process ParGCArrayScanChunk elements now
// and push the remainder back onto queue
int start = arrayOop(old)->length();
int end = obj->length();
int remainder = end - start;
assert(start <= end, "just checking");
if (remainder > 2 * ParGCArrayScanChunk) {
// Test above combines last partial chunk with a full chunk
end = start + ParGCArrayScanChunk;
arrayOop(old)->set_length(end);
// Push remainder.
bool ok = work_queue()->push(old);
assert(ok, "just popped, push must be okay");
note_push();
} else {
// Restore length so that it can be used if there
// is a promotion failure and forwarding pointers
// must be removed.
arrayOop(old)->set_length(end);
}
// process our set of indices (include header in first chunk)
// should make sure end is even (aligned to HeapWord in case of compressed oops)
if ((HeapWord *)obj < young_old_boundary()) {
// object is in to_space
obj->oop_iterate_range(&_to_space_closure, start, end);
} else {
// object is in old generation
obj->oop_iterate_range(&_old_gen_closure, start, end);
}
}
void ParScanThreadState::trim_queues(int max_size) {
ObjToScanQueue* queue = work_queue();
do {
while (queue->size() > (juint)max_size) {
oop obj_to_scan;
if (queue->pop_local(obj_to_scan)) {
note_pop();
if ((HeapWord *)obj_to_scan < young_old_boundary()) {
if (obj_to_scan->is_objArray() &&
obj_to_scan->is_forwarded() &&
obj_to_scan->forwardee() != obj_to_scan) {
scan_partial_array_and_push_remainder(obj_to_scan);
} else {
// object is in to_space
obj_to_scan->oop_iterate(&_to_space_closure);
}
} else {
// object is in old generation
obj_to_scan->oop_iterate(&_old_gen_closure);
}
}
}
// For the case of compressed oops, we have a private, non-shared
// overflow stack, so we eagerly drain it so as to more evenly
// distribute load early. Note: this may be good to do in
// general rather than delay for the final stealing phase.
// If applicable, we'll transfer a set of objects over to our
// work queue, allowing them to be stolen and draining our
// private overflow stack.
} while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this));
}
bool ParScanThreadState::take_from_overflow_stack() {
assert(UseCompressedOops, "Else should not call");
assert(young_gen()->overflow_list() == NULL, "Error");
ObjToScanQueue* queue = work_queue();
GrowableArray<oop>* of_stack = overflow_stack();
uint num_overflow_elems = of_stack->length();
uint num_take_elems = MIN2(MIN2((queue->max_elems() - queue->size())/4,
(juint)ParGCDesiredObjsFromOverflowList),
num_overflow_elems);
// Transfer the most recent num_take_elems from the overflow
// stack to our work queue.
for (size_t i = 0; i != num_take_elems; i++) {
oop cur = of_stack->pop();
oop obj_to_push = cur->forwardee();
assert(Universe::heap()->is_in_reserved(cur), "Should be in heap");
assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");
assert(Universe::heap()->is_in_reserved(obj_to_push), "Should be in heap");
if (should_be_partially_scanned(obj_to_push, cur)) {
assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
obj_to_push = cur;
}
bool ok = queue->push(obj_to_push);
assert(ok, "Should have succeeded");
}
assert(young_gen()->overflow_list() == NULL, "Error");
return num_take_elems > 0; // was something transferred?
}
void ParScanThreadState::push_on_overflow_stack(oop p) {
assert(UseCompressedOops, "Else should not call");
overflow_stack()->push(p);
assert(young_gen()->overflow_list() == NULL, "Error");
}
HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {
// Otherwise, if the object is small enough, try to reallocate the
// buffer.
HeapWord* obj = NULL;
if (!_to_space_full) {
ParGCAllocBuffer* const plab = to_space_alloc_buffer();
Space* const sp = to_space();
if (word_sz * 100 <
ParallelGCBufferWastePct * plab->word_sz()) {
// Is small enough; abandon this buffer and start a new one.
plab->retire(false, false);
size_t buf_size = plab->word_sz();
HeapWord* buf_space = sp->par_allocate(buf_size);
if (buf_space == NULL) {
const size_t min_bytes =
ParGCAllocBuffer::min_size() << LogHeapWordSize;
size_t free_bytes = sp->free();
while(buf_space == NULL && free_bytes >= min_bytes) {
buf_size = free_bytes >> LogHeapWordSize;
assert(buf_size == (size_t)align_object_size(buf_size),
"Invariant");
buf_space = sp->par_allocate(buf_size);
free_bytes = sp->free();
}
}
if (buf_space != NULL) {
plab->set_word_size(buf_size);
plab->set_buf(buf_space);
record_survivor_plab(buf_space, buf_size);
obj = plab->allocate(word_sz);
// Note that we cannot compare buf_size < word_sz below
// because of AlignmentReserve (see ParGCAllocBuffer::allocate()).
assert(obj != NULL || plab->words_remaining() < word_sz,
"Else should have been able to allocate");
// It's conceivable that we may be able to use the
// buffer we just grabbed for subsequent small requests
// even if not for this one.
} else {
// We're used up.
_to_space_full = true;
}
} else {
// Too large; allocate the object individually.
obj = sp->par_allocate(word_sz);
}
}
return obj;
}
void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj,
size_t word_sz) {
// Is the alloc in the current alloc buffer?
if (to_space_alloc_buffer()->contains(obj)) {
assert(to_space_alloc_buffer()->contains(obj + word_sz - 1),
"Should contain whole object.");
to_space_alloc_buffer()->undo_allocation(obj, word_sz);
} else {
CollectedHeap::fill_with_object(obj, word_sz);
}
}
class ParScanThreadStateSet: private ResourceArray {
public:
// Initializes states for the specified number of threads;
ParScanThreadStateSet(int num_threads,
Space& to_space,
ParNewGeneration& gen,
Generation& old_gen,
ObjToScanQueueSet& queue_set,
size_t desired_plab_sz,
ParallelTaskTerminator& term);
inline ParScanThreadState& thread_sate(int i);
int pushes() { return _pushes; }
int pops() { return _pops; }
int steals() { return _steals; }
void reset();
void flush();
private:
ParallelTaskTerminator& _term;
ParNewGeneration& _gen;
Generation& _next_gen;
// staticstics
int _pushes;
int _pops;
int _steals;
};
ParScanThreadStateSet::ParScanThreadStateSet(
int num_threads, Space& to_space, ParNewGeneration& gen,
Generation& old_gen, ObjToScanQueueSet& queue_set,
size_t desired_plab_sz, ParallelTaskTerminator& term)
: ResourceArray(sizeof(ParScanThreadState), num_threads),
_gen(gen), _next_gen(old_gen), _term(term),
_pushes(0), _pops(0), _steals(0)
{
assert(num_threads > 0, "sanity check!");
// Initialize states.
for (int i = 0; i < num_threads; ++i) {
new ((ParScanThreadState*)_data + i)
ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set,
desired_plab_sz, term);
}
}
inline ParScanThreadState& ParScanThreadStateSet::thread_sate(int i)
{
assert(i >= 0 && i < length(), "sanity check!");
return ((ParScanThreadState*)_data)[i];
}
void ParScanThreadStateSet::reset()
{
_term.reset_for_reuse();
}
void ParScanThreadStateSet::flush()
{
for (int i = 0; i < length(); ++i) {
ParScanThreadState& par_scan_state = thread_sate(i);
// Flush stats related to To-space PLAB activity and
// retire the last buffer.
par_scan_state.to_space_alloc_buffer()->
flush_stats_and_retire(_gen.plab_stats(),
false /* !retain */);
// Every thread has its own age table. We need to merge
// them all into one.
ageTable *local_table = par_scan_state.age_table();
_gen.age_table()->merge(local_table);
// Inform old gen that we're done.
_next_gen.par_promote_alloc_done(i);
_next_gen.par_oop_since_save_marks_iterate_done(i);
// Flush stats related to work queue activity (push/pop/steal)
// This could conceivably become a bottleneck; if so, we'll put the
// stat's gathering under the flag.
if (PAR_STATS_ENABLED) {
_pushes += par_scan_state.pushes();
_pops += par_scan_state.pops();
_steals += par_scan_state.steals();
if (ParallelGCVerbose) {
gclog_or_tty->print("Thread %d complete:\n"
" Pushes: %7d Pops: %7d Steals %7d (in %d attempts)\n",
i, par_scan_state.pushes(), par_scan_state.pops(),
par_scan_state.steals(), par_scan_state.steal_attempts());
if (par_scan_state.overflow_pushes() > 0 ||
par_scan_state.overflow_refills() > 0) {
gclog_or_tty->print(" Overflow pushes: %7d "
"Overflow refills: %7d for %d objs.\n",
par_scan_state.overflow_pushes(),
par_scan_state.overflow_refills(),
par_scan_state.overflow_refill_objs());
}
double elapsed = par_scan_state.elapsed();
double strong_roots = par_scan_state.strong_roots_time();
double term = par_scan_state.term_time();
gclog_or_tty->print(
" Elapsed: %7.2f ms.\n"
" Strong roots: %7.2f ms (%6.2f%%)\n"
" Termination: %7.2f ms (%6.2f%%) (in %d entries)\n",
elapsed * 1000.0,
strong_roots * 1000.0, (strong_roots*100.0/elapsed),
term * 1000.0, (term*100.0/elapsed),
par_scan_state.term_attempts());
}
}
}
}
ParScanClosure::ParScanClosure(ParNewGeneration* g,
ParScanThreadState* par_scan_state) :
OopsInGenClosure(g), _par_scan_state(par_scan_state), _g(g)
{
assert(_g->level() == 0, "Optimized for youngest generation");
_boundary = _g->reserved().end();
}
void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); }
void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); }
void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); }
void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); }
void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); }
void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); }
void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); }
void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); }
ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,
ParScanThreadState* par_scan_state)
: ScanWeakRefClosure(g), _par_scan_state(par_scan_state)
{}
void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); }
void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); }
#ifdef WIN32
#pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */
#endif
ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(
ParScanThreadState* par_scan_state_,
ParScanWithoutBarrierClosure* to_space_closure_,
ParScanWithBarrierClosure* old_gen_closure_,
ParRootScanWithoutBarrierClosure* to_space_root_closure_,
ParNewGeneration* par_gen_,
ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,
ObjToScanQueueSet* task_queues_,
ParallelTaskTerminator* terminator_) :
_par_scan_state(par_scan_state_),
_to_space_closure(to_space_closure_),
_old_gen_closure(old_gen_closure_),
_to_space_root_closure(to_space_root_closure_),
_old_gen_root_closure(old_gen_root_closure_),
_par_gen(par_gen_),
_task_queues(task_queues_),
_terminator(terminator_)
{}
void ParEvacuateFollowersClosure::do_void() {
ObjToScanQueue* work_q = par_scan_state()->work_queue();
while (true) {
// Scan to-space and old-gen objs until we run out of both.
oop obj_to_scan;
par_scan_state()->trim_queues(0);
// We have no local work, attempt to steal from other threads.
// attempt to steal work from promoted.
par_scan_state()->note_steal_attempt();
if (task_queues()->steal(par_scan_state()->thread_num(),
par_scan_state()->hash_seed(),
obj_to_scan)) {
par_scan_state()->note_steal();
bool res = work_q->push(obj_to_scan);
assert(res, "Empty queue should have room for a push.");
par_scan_state()->note_push();
// if successful, goto Start.
continue;
// try global overflow list.
} else if (par_gen()->take_from_overflow_list(par_scan_state())) {
continue;
}
// Otherwise, offer termination.
par_scan_state()->start_term_time();
if (terminator()->offer_termination()) break;
par_scan_state()->end_term_time();
}
assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0,
"Broken overflow list?");
// Finish the last termination pause.
par_scan_state()->end_term_time();
}
ParNewGenTask::ParNewGenTask(ParNewGeneration* gen, Generation* next_gen,
HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) :
AbstractGangTask("ParNewGeneration collection"),
_gen(gen), _next_gen(next_gen),
_young_old_boundary(young_old_boundary),
_state_set(state_set)
{}
void ParNewGenTask::work(int i) {
GenCollectedHeap* gch = GenCollectedHeap::heap();
// Since this is being done in a separate thread, need new resource
// and handle marks.
ResourceMark rm;
HandleMark hm;
// We would need multiple old-gen queues otherwise.
assert(gch->n_gens() == 2, "Par young collection currently only works with one older gen.");
Generation* old_gen = gch->next_gen(_gen);
ParScanThreadState& par_scan_state = _state_set->thread_sate(i);
par_scan_state.set_young_old_boundary(_young_old_boundary);
par_scan_state.start_strong_roots();
gch->gen_process_strong_roots(_gen->level(),
true, // Process younger gens, if any,
// as strong roots.
false,// not collecting perm generation.
SharedHeap::SO_AllClasses,
&par_scan_state.older_gen_closure(),
&par_scan_state.to_space_root_closure());
par_scan_state.end_strong_roots();
// "evacuate followers".
par_scan_state.evacuate_followers_closure().do_void();
}
#ifdef _MSC_VER
#pragma warning( push )
#pragma warning( disable:4355 ) // 'this' : used in base member initializer list
#endif
ParNewGeneration::
ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level)
: DefNewGeneration(rs, initial_byte_size, level, "PCopy"),
_overflow_list(NULL),
_is_alive_closure(this),
_plab_stats(YoungPLABSize, PLABWeight)
{
NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
NOT_PRODUCT(_num_par_pushes = 0;)
_task_queues = new ObjToScanQueueSet(ParallelGCThreads);
guarantee(_task_queues != NULL, "task_queues allocation failure.");
for (uint i1 = 0; i1 < ParallelGCThreads; i1++) {
ObjToScanQueuePadded *q_padded = new ObjToScanQueuePadded();
guarantee(q_padded != NULL, "work_queue Allocation failure.");
_task_queues->register_queue(i1, &q_padded->work_queue);
}
for (uint i2 = 0; i2 < ParallelGCThreads; i2++)
_task_queues->queue(i2)->initialize();
if (UsePerfData) {
EXCEPTION_MARK;
ResourceMark rm;
const char* cname =
PerfDataManager::counter_name(_gen_counters->name_space(), "threads");
PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
ParallelGCThreads, CHECK);
}
}
#ifdef _MSC_VER
#pragma warning( pop )
#endif
// ParNewGeneration::
ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
template <class T>
void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
#ifdef ASSERT
{
assert(!oopDesc::is_null(*p), "expected non-null ref");
oop obj = oopDesc::load_decode_heap_oop_not_null(p);
// We never expect to see a null reference being processed
// as a weak reference.
assert(obj->is_oop(), "expected an oop while scanning weak refs");
}
#endif // ASSERT
_par_cl->do_oop_nv(p);
if (Universe::heap()->is_in_reserved(p)) {
oop obj = oopDesc::load_decode_heap_oop_not_null(p);
_rs->write_ref_field_gc_par(p, obj);
}
}
void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); }
void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }
// ParNewGeneration::
KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :
DefNewGeneration::KeepAliveClosure(cl) {}
template <class T>
void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {
#ifdef ASSERT
{
assert(!oopDesc::is_null(*p), "expected non-null ref");
oop obj = oopDesc::load_decode_heap_oop_not_null(p);
// We never expect to see a null reference being processed
// as a weak reference.
assert(obj->is_oop(), "expected an oop while scanning weak refs");
}
#endif // ASSERT
_cl->do_oop_nv(p);
if (Universe::heap()->is_in_reserved(p)) {
oop obj = oopDesc::load_decode_heap_oop_not_null(p);
_rs->write_ref_field_gc_par(p, obj);
}
}
void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); }
void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }
template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {
T heap_oop = oopDesc::load_heap_oop(p);
if (!oopDesc::is_null(heap_oop)) {
oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
if ((HeapWord*)obj < _boundary) {
assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
oop new_obj = obj->is_forwarded()
? obj->forwardee()
: _g->DefNewGeneration::copy_to_survivor_space(obj);
oopDesc::encode_store_heap_oop_not_null(p, new_obj);
}
if (_gc_barrier) {
// If p points to a younger generation, mark the card.
if ((HeapWord*)obj < _gen_boundary) {
_rs->write_ref_field_gc_par(p, obj);
}
}
}
}
void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
class ParNewRefProcTaskProxy: public AbstractGangTask {
typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
public:
ParNewRefProcTaskProxy(ProcessTask& task, ParNewGeneration& gen,
Generation& next_gen,
HeapWord* young_old_boundary,
ParScanThreadStateSet& state_set);
private:
virtual void work(int i);
private:
ParNewGeneration& _gen;
ProcessTask& _task;
Generation& _next_gen;
HeapWord* _young_old_boundary;
ParScanThreadStateSet& _state_set;
};
ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(
ProcessTask& task, ParNewGeneration& gen,
Generation& next_gen,
HeapWord* young_old_boundary,
ParScanThreadStateSet& state_set)
: AbstractGangTask("ParNewGeneration parallel reference processing"),
_gen(gen),
_task(task),
_next_gen(next_gen),
_young_old_boundary(young_old_boundary),
_state_set(state_set)
{
}
void ParNewRefProcTaskProxy::work(int i)
{
ResourceMark rm;
HandleMark hm;
ParScanThreadState& par_scan_state = _state_set.thread_sate(i);
par_scan_state.set_young_old_boundary(_young_old_boundary);
_task.work(i, par_scan_state.is_alive_closure(),
par_scan_state.keep_alive_closure(),
par_scan_state.evacuate_followers_closure());
}
class ParNewRefEnqueueTaskProxy: public AbstractGangTask {
typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
EnqueueTask& _task;
public:
ParNewRefEnqueueTaskProxy(EnqueueTask& task)
: AbstractGangTask("ParNewGeneration parallel reference enqueue"),
_task(task)
{ }
virtual void work(int i)
{
_task.work(i);
}
};
void ParNewRefProcTaskExecutor::execute(ProcessTask& task)
{
GenCollectedHeap* gch = GenCollectedHeap::heap();
assert(gch->kind() == CollectedHeap::GenCollectedHeap,
"not a generational heap");
WorkGang* workers = gch->workers();
assert(workers != NULL, "Need parallel worker threads.");
ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(),
_generation.reserved().end(), _state_set);
workers->run_task(&rp_task);
_state_set.reset();
}
void ParNewRefProcTaskExecutor::execute(EnqueueTask& task)
{
GenCollectedHeap* gch = GenCollectedHeap::heap();
WorkGang* workers = gch->workers();
assert(workers != NULL, "Need parallel worker threads.");
ParNewRefEnqueueTaskProxy enq_task(task);
workers->run_task(&enq_task);
}
void ParNewRefProcTaskExecutor::set_single_threaded_mode()
{
_state_set.flush();
GenCollectedHeap* gch = GenCollectedHeap::heap();
gch->set_par_threads(0); // 0 ==> non-parallel.
gch->save_marks();
}
ScanClosureWithParBarrier::
ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
ScanClosure(g, gc_barrier) {}
EvacuateFollowersClosureGeneral::
EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level,
OopsInGenClosure* cur,
OopsInGenClosure* older) :
_gch(gch), _level(level),
_scan_cur_or_nonheap(cur), _scan_older(older)
{}
void EvacuateFollowersClosureGeneral::do_void() {
do {
// Beware: this call will lead to closure applications via virtual
// calls.
_gch->oop_since_save_marks_iterate(_level,
_scan_cur_or_nonheap,
_scan_older);
} while (!_gch->no_allocs_since_save_marks(_level));
}
bool ParNewGeneration::_avoid_promotion_undo = false;
void ParNewGeneration::adjust_desired_tenuring_threshold() {
// Set the desired survivor size to half the real survivor space
_tenuring_threshold =
age_table()->compute_tenuring_threshold(to()->capacity()/HeapWordSize);
}
// A Generation that does parallel young-gen collection.
void ParNewGeneration::collect(bool full,
bool clear_all_soft_refs,
size_t size,
bool is_tlab) {
assert(full || size > 0, "otherwise we don't want to collect");
GenCollectedHeap* gch = GenCollectedHeap::heap();
assert(gch->kind() == CollectedHeap::GenCollectedHeap,
"not a CMS generational heap");
AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy();
WorkGang* workers = gch->workers();
_next_gen = gch->next_gen(this);
assert(_next_gen != NULL,
"This must be the youngest gen, and not the only gen");
assert(gch->n_gens() == 2,
"Par collection currently only works with single older gen.");
// Do we have to avoid promotion_undo?
if (gch->collector_policy()->is_concurrent_mark_sweep_policy()) {
set_avoid_promotion_undo(true);
}
// If the next generation is too full to accomodate worst-case promotion
// from this generation, pass on collection; let the next generation
// do it.
if (!collection_attempt_is_safe()) {
gch->set_incremental_collection_will_fail();
return;
}
assert(to()->is_empty(), "Else not collection_attempt_is_safe");
init_assuming_no_promotion_failure();
if (UseAdaptiveSizePolicy) {
set_survivor_overflow(false);
size_policy->minor_collection_begin();
}
TraceTime t1("GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);
// Capture heap used before collection (for printing).
size_t gch_prev_used = gch->used();
SpecializationStats::clear();
age_table()->clear();
to()->clear(SpaceDecorator::Mangle);
gch->save_marks();
assert(workers != NULL, "Need parallel worker threads.");
ParallelTaskTerminator _term(workers->total_workers(), task_queues());
ParScanThreadStateSet thread_state_set(workers->total_workers(),
*to(), *this, *_next_gen, *task_queues(),
desired_plab_sz(), _term);
ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set);
int n_workers = workers->total_workers();
gch->set_par_threads(n_workers);
gch->change_strong_roots_parity();
gch->rem_set()->prepare_for_younger_refs_iterate(true);
// It turns out that even when we're using 1 thread, doing the work in a
// separate thread causes wide variance in run times. We can't help this
// in the multi-threaded case, but we special-case n=1 here to get
// repeatable measurements of the 1-thread overhead of the parallel code.
if (n_workers > 1) {
workers->run_task(&tsk);
} else {
tsk.work(0);
}
thread_state_set.reset();
if (PAR_STATS_ENABLED && ParallelGCVerbose) {
gclog_or_tty->print("Thread totals:\n"
" Pushes: %7d Pops: %7d Steals %7d (sum = %7d).\n",
thread_state_set.pushes(), thread_state_set.pops(),
thread_state_set.steals(),
thread_state_set.pops()+thread_state_set.steals());
}
assert(thread_state_set.pushes() == thread_state_set.pops()
+ thread_state_set.steals(),
"Or else the queues are leaky.");
// Process (weak) reference objects found during scavenge.
ReferenceProcessor* rp = ref_processor();
IsAliveClosure is_alive(this);
ScanWeakRefClosure scan_weak_ref(this);
KeepAliveClosure keep_alive(&scan_weak_ref);
ScanClosure scan_without_gc_barrier(this, false);
ScanClosureWithParBarrier scan_with_gc_barrier(this, true);
set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
EvacuateFollowersClosureGeneral evacuate_followers(gch, _level,
&scan_without_gc_barrier, &scan_with_gc_barrier);
rp->setup_policy(clear_all_soft_refs);
if (rp->processing_is_mt()) {
ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
rp->process_discovered_references(&is_alive, &keep_alive,
&evacuate_followers, &task_executor);
} else {
thread_state_set.flush();
gch->set_par_threads(0); // 0 ==> non-parallel.
gch->save_marks();
rp->process_discovered_references(&is_alive, &keep_alive,
&evacuate_followers, NULL);
}
if (!promotion_failed()) {
// Swap the survivor spaces.
eden()->clear(SpaceDecorator::Mangle);
from()->clear(SpaceDecorator::Mangle);
if (ZapUnusedHeapArea) {
// This is now done here because of the piece-meal mangling which
// can check for valid mangling at intermediate points in the
// collection(s). When a minor collection fails to collect
// sufficient space resizing of the young generation can occur
// an redistribute the spaces in the young generation. Mangle
// here so that unzapped regions don't get distributed to
// other spaces.
to()->mangle_unused_area();
}
swap_spaces();
assert(to()->is_empty(), "to space should be empty now");
} else {
assert(HandlePromotionFailure,
"Should only be here if promotion failure handling is on");
if (_promo_failure_scan_stack != NULL) {
// Can be non-null because of reference processing.
// Free stack with its elements.
delete _promo_failure_scan_stack;
_promo_failure_scan_stack = NULL;
}
remove_forwarding_pointers();
if (PrintGCDetails) {
gclog_or_tty->print(" (promotion failed)");
}
// All the spaces are in play for mark-sweep.
swap_spaces(); // Make life simpler for CMS || rescan; see 6483690.
from()->set_next_compaction_space(to());
gch->set_incremental_collection_will_fail();
// Reset the PromotionFailureALot counters.
NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();)
}
// set new iteration safe limit for the survivor spaces
from()->set_concurrent_iteration_safe_limit(from()->top());
to()->set_concurrent_iteration_safe_limit(to()->top());
adjust_desired_tenuring_threshold();
if (ResizePLAB) {
plab_stats()->adjust_desired_plab_sz();
}
if (PrintGC && !PrintGCDetails) {
gch->print_heap_change(gch_prev_used);
}
if (UseAdaptiveSizePolicy) {
size_policy->minor_collection_end(gch->gc_cause());
size_policy->avg_survived()->sample(from()->used());
}
update_time_of_last_gc(os::javaTimeMillis());
SpecializationStats::print();
rp->set_enqueuing_is_done(true);
if (rp->processing_is_mt()) {
ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
rp->enqueue_discovered_references(&task_executor);
} else {
rp->enqueue_discovered_references(NULL);
}
rp->verify_no_references_recorded();
}
static int sum;
void ParNewGeneration::waste_some_time() {
for (int i = 0; i < 100; i++) {
sum += i;
}
}
static const oop ClaimedForwardPtr = oop(0x4);
// Because of concurrency, there are times where an object for which
// "is_forwarded()" is true contains an "interim" forwarding pointer
// value. Such a value will soon be overwritten with a real value.
// This method requires "obj" to have a forwarding pointer, and waits, if
// necessary for a real one to be inserted, and returns it.
oop ParNewGeneration::real_forwardee(oop obj) {
oop forward_ptr = obj->forwardee();
if (forward_ptr != ClaimedForwardPtr) {
return forward_ptr;
} else {
return real_forwardee_slow(obj);
}
}
oop ParNewGeneration::real_forwardee_slow(oop obj) {
// Spin-read if it is claimed but not yet written by another thread.
oop forward_ptr = obj->forwardee();
while (forward_ptr == ClaimedForwardPtr) {
waste_some_time();
assert(obj->is_forwarded(), "precondition");
forward_ptr = obj->forwardee();
}
return forward_ptr;
}
#ifdef ASSERT
bool ParNewGeneration::is_legal_forward_ptr(oop p) {
return
(_avoid_promotion_undo && p == ClaimedForwardPtr)
|| Universe::heap()->is_in_reserved(p);
}
#endif
void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) {
if ((m != markOopDesc::prototype()) &&
(!UseBiasedLocking || (m != markOopDesc::biased_locking_prototype()))) {
MutexLocker ml(ParGCRareEvent_lock);
DefNewGeneration::preserve_mark_if_necessary(obj, m);
}
}
// Multiple GC threads may try to promote an object. If the object
// is successfully promoted, a forwarding pointer will be installed in
// the object in the young generation. This method claims the right
// to install the forwarding pointer before it copies the object,
// thus avoiding the need to undo the copy as in
// copy_to_survivor_space_avoiding_with_undo.
oop ParNewGeneration::copy_to_survivor_space_avoiding_promotion_undo(
ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
// In the sequential version, this assert also says that the object is
// not forwarded. That might not be the case here. It is the case that
// the caller observed it to be not forwarded at some time in the past.
assert(is_in_reserved(old), "shouldn't be scavenging this oop");
// The sequential code read "old->age()" below. That doesn't work here,
// since the age is in the mark word, and that might be overwritten with
// a forwarding pointer by a parallel thread. So we must save the mark
// word in a local and then analyze it.
oopDesc dummyOld;
dummyOld.set_mark(m);
assert(!dummyOld.is_forwarded(),
"should not be called with forwarding pointer mark word.");
oop new_obj = NULL;
oop forward_ptr;
// Try allocating obj in to-space (unless too old)
if (dummyOld.age() < tenuring_threshold()) {
new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
if (new_obj == NULL) {
set_survivor_overflow(true);
}
}
if (new_obj == NULL) {
// Either to-space is full or we decided to promote
// try allocating obj tenured
// Attempt to install a null forwarding pointer (atomically),
// to claim the right to install the real forwarding pointer.
forward_ptr = old->forward_to_atomic(ClaimedForwardPtr);
if (forward_ptr != NULL) {
// someone else beat us to it.
return real_forwardee(old);
}
new_obj = _next_gen->par_promote(par_scan_state->thread_num(),
old, m, sz);
if (new_obj == NULL) {
if (!HandlePromotionFailure) {
// A failed promotion likely means the MaxLiveObjectEvacuationRatio flag
// is incorrectly set. In any case, its seriously wrong to be here!
vm_exit_out_of_memory(sz*wordSize, "promotion");
}
// promotion failed, forward to self
_promotion_failed = true;
new_obj = old;
preserve_mark_if_necessary(old, m);
}
old->forward_to(new_obj);
forward_ptr = NULL;
} else {
// Is in to-space; do copying ourselves.
Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
forward_ptr = old->forward_to_atomic(new_obj);
// Restore the mark word copied above.
new_obj->set_mark(m);
// Increment age if obj still in new generation
new_obj->incr_age();
par_scan_state->age_table()->add(new_obj, sz);
}
assert(new_obj != NULL, "just checking");
if (forward_ptr == NULL) {
oop obj_to_push = new_obj;
if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
// Length field used as index of next element to be scanned.
// Real length can be obtained from real_forwardee()
arrayOop(old)->set_length(0);
obj_to_push = old;
assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
"push forwarded object");
}
// Push it on one of the queues of to-be-scanned objects.
bool simulate_overflow = false;
NOT_PRODUCT(
if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
// simulate a stack overflow
simulate_overflow = true;
}
)
if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
// Add stats for overflow pushes.
if (Verbose && PrintGCDetails) {
gclog_or_tty->print("queue overflow!\n");
}
push_on_overflow_list(old, par_scan_state);
par_scan_state->note_overflow_push();
}
par_scan_state->note_push();
return new_obj;
}
// Oops. Someone beat us to it. Undo the allocation. Where did we
// allocate it?
if (is_in_reserved(new_obj)) {
// Must be in to_space.
assert(to()->is_in_reserved(new_obj), "Checking");
if (forward_ptr == ClaimedForwardPtr) {
// Wait to get the real forwarding pointer value.
forward_ptr = real_forwardee(old);
}
par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
}
return forward_ptr;
}
// Multiple GC threads may try to promote the same object. If two
// or more GC threads copy the object, only one wins the race to install
// the forwarding pointer. The other threads have to undo their copy.
oop ParNewGeneration::copy_to_survivor_space_with_undo(
ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
// In the sequential version, this assert also says that the object is
// not forwarded. That might not be the case here. It is the case that
// the caller observed it to be not forwarded at some time in the past.
assert(is_in_reserved(old), "shouldn't be scavenging this oop");
// The sequential code read "old->age()" below. That doesn't work here,
// since the age is in the mark word, and that might be overwritten with
// a forwarding pointer by a parallel thread. So we must save the mark
// word here, install it in a local oopDesc, and then analyze it.
oopDesc dummyOld;
dummyOld.set_mark(m);
assert(!dummyOld.is_forwarded(),
"should not be called with forwarding pointer mark word.");
bool failed_to_promote = false;
oop new_obj = NULL;
oop forward_ptr;
// Try allocating obj in to-space (unless too old)
if (dummyOld.age() < tenuring_threshold()) {
new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
if (new_obj == NULL) {
set_survivor_overflow(true);
}
}
if (new_obj == NULL) {
// Either to-space is full or we decided to promote
// try allocating obj tenured
new_obj = _next_gen->par_promote(par_scan_state->thread_num(),
old, m, sz);
if (new_obj == NULL) {
if (!HandlePromotionFailure) {
// A failed promotion likely means the MaxLiveObjectEvacuationRatio
// flag is incorrectly set. In any case, its seriously wrong to be
// here!
vm_exit_out_of_memory(sz*wordSize, "promotion");
}
// promotion failed, forward to self
forward_ptr = old->forward_to_atomic(old);
new_obj = old;
if (forward_ptr != NULL) {
return forward_ptr; // someone else succeeded
}
_promotion_failed = true;
failed_to_promote = true;
preserve_mark_if_necessary(old, m);
}
} else {
// Is in to-space; do copying ourselves.
Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
// Restore the mark word copied above.
new_obj->set_mark(m);
// Increment age if new_obj still in new generation
new_obj->incr_age();
par_scan_state->age_table()->add(new_obj, sz);
}
assert(new_obj != NULL, "just checking");
// Now attempt to install the forwarding pointer (atomically).
// We have to copy the mark word before overwriting with forwarding
// ptr, so we can restore it below in the copy.
if (!failed_to_promote) {
forward_ptr = old->forward_to_atomic(new_obj);
}
if (forward_ptr == NULL) {
oop obj_to_push = new_obj;
if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
// Length field used as index of next element to be scanned.
// Real length can be obtained from real_forwardee()
arrayOop(old)->set_length(0);
obj_to_push = old;
assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
"push forwarded object");
}
// Push it on one of the queues of to-be-scanned objects.
bool simulate_overflow = false;
NOT_PRODUCT(
if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
// simulate a stack overflow
simulate_overflow = true;
}
)
if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
// Add stats for overflow pushes.
push_on_overflow_list(old, par_scan_state);
par_scan_state->note_overflow_push();
}
par_scan_state->note_push();
return new_obj;
}
// Oops. Someone beat us to it. Undo the allocation. Where did we
// allocate it?
if (is_in_reserved(new_obj)) {
// Must be in to_space.
assert(to()->is_in_reserved(new_obj), "Checking");
par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
} else {
assert(!_avoid_promotion_undo, "Should not be here if avoiding.");
_next_gen->par_promote_alloc_undo(par_scan_state->thread_num(),
(HeapWord*)new_obj, sz);
}
return forward_ptr;
}
#ifndef PRODUCT
// It's OK to call this multi-threaded; the worst thing
// that can happen is that we'll get a bunch of closely
// spaced simulated oveflows, but that's OK, in fact
// probably good as it would exercise the overflow code
// under contention.
bool ParNewGeneration::should_simulate_overflow() {
if (_overflow_counter-- <= 0) { // just being defensive
_overflow_counter = ParGCWorkQueueOverflowInterval;
return true;
} else {
return false;
}
}
#endif
// In case we are using compressed oops, we need to be careful.
// If the object being pushed is an object array, then its length
// field keeps track of the "grey boundary" at which the next
// incremental scan will be done (see ParGCArrayScanChunk).
// When using compressed oops, this length field is kept in the
// lower 32 bits of the erstwhile klass word and cannot be used
// for the overflow chaining pointer (OCP below). As such the OCP
// would itself need to be compressed into the top 32-bits in this
// case. Unfortunately, see below, in the event that we have a
// promotion failure, the node to be pushed on the list can be
// outside of the Java heap, so the heap-based pointer compression
// would not work (we would have potential aliasing between C-heap
// and Java-heap pointers). For this reason, when using compressed
// oops, we simply use a worker-thread-local, non-shared overflow
// list in the form of a growable array, with a slightly different
// overflow stack draining strategy. If/when we start using fat
// stacks here, we can go back to using (fat) pointer chains
// (although some performance comparisons would be useful since
// single global lists have their own performance disadvantages
// as we were made painfully aware not long ago, see 6786503).
#define BUSY (oop(0x1aff1aff))
void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
assert(is_in_reserved(from_space_obj), "Should be from this generation");
if (UseCompressedOops) {
// In the case of compressed oops, we use a private, not-shared
// overflow stack.
par_scan_state->push_on_overflow_stack(from_space_obj);
} else {
// if the object has been forwarded to itself, then we cannot
// use the klass pointer for the linked list. Instead we have
// to allocate an oopDesc in the C-Heap and use that for the linked list.
// XXX This is horribly inefficient when a promotion failure occurs
// and should be fixed. XXX FIX ME !!!
#ifndef PRODUCT
Atomic::inc_ptr(&_num_par_pushes);
assert(_num_par_pushes > 0, "Tautology");
#endif
if (from_space_obj->forwardee() == from_space_obj) {
oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1);
listhead->forward_to(from_space_obj);
from_space_obj = listhead;
}
oop observed_overflow_list = _overflow_list;
oop cur_overflow_list;
do {
cur_overflow_list = observed_overflow_list;
if (cur_overflow_list != BUSY) {
from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
} else {
from_space_obj->set_klass_to_list_ptr(NULL);
}
observed_overflow_list =
(oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);
} while (cur_overflow_list != observed_overflow_list);
}
}
bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
bool res;
if (UseCompressedOops) {
res = par_scan_state->take_from_overflow_stack();
} else {
res = take_from_overflow_list_work(par_scan_state);
}
return res;
}
// *NOTE*: The overflow list manipulation code here and
// in CMSCollector:: are very similar in shape,
// except that in the CMS case we thread the objects
// directly into the list via their mark word, and do
// not need to deal with special cases below related
// to chunking of object arrays and promotion failure
// handling.
// CR 6797058 has been filed to attempt consolidation of
// the common code.
// Because of the common code, if you make any changes in
// the code below, please check the CMS version to see if
// similar changes might be needed.
// See CMSCollector::par_take_from_overflow_list() for
// more extensive documentation comments.
bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
ObjToScanQueue* work_q = par_scan_state->work_queue();
// How many to take?
size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
(size_t)ParGCDesiredObjsFromOverflowList);
assert(par_scan_state->overflow_stack() == NULL, "Error");
if (_overflow_list == NULL) return false;
// Otherwise, there was something there; try claiming the list.
oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
// Trim off a prefix of at most objsFromOverflow items
Thread* tid = Thread::current();
size_t spin_count = (size_t)ParallelGCThreads;
size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);
for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {
// someone grabbed it before we did ...
// ... we spin for a short while...
os::sleep(tid, sleep_time_millis, false);
if (_overflow_list == NULL) {
// nothing left to take
return false;
} else if (_overflow_list != BUSY) {
// try and grab the prefix
prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
}
}
if (prefix == NULL || prefix == BUSY) {
// Nothing to take or waited long enough
if (prefix == NULL) {
// Write back the NULL in case we overwrote it with BUSY above
// and it is still the same value.
(void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
}
return false;
}
assert(prefix != NULL && prefix != BUSY, "Error");
size_t i = 1;
oop cur = prefix;
while (i < objsFromOverflow && cur->klass_or_null() != NULL) {
i++; cur = oop(cur->klass());
}
// Reattach remaining (suffix) to overflow list
if (cur->klass_or_null() == NULL) {
// Write back the NULL in lieu of the BUSY we wrote
// above and it is still the same value.
if (_overflow_list == BUSY) {
(void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
}
} else {
assert(cur->klass_or_null() != BUSY, "Error");
oop suffix = oop(cur->klass()); // suffix will be put back on global list
cur->set_klass_to_list_ptr(NULL); // break off suffix
// It's possible that the list is still in the empty(busy) state
// we left it in a short while ago; in that case we may be
// able to place back the suffix.
oop observed_overflow_list = _overflow_list;
oop cur_overflow_list = observed_overflow_list;
bool attached = false;
while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
observed_overflow_list =
(oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
if (cur_overflow_list == observed_overflow_list) {
attached = true;
break;
} else cur_overflow_list = observed_overflow_list;
}
if (!attached) {
// Too bad, someone else got in in between; we'll need to do a splice.
// Find the last item of suffix list
oop last = suffix;
while (last->klass_or_null() != NULL) {
last = oop(last->klass());
}
// Atomically prepend suffix to current overflow list
observed_overflow_list = _overflow_list;
do {
cur_overflow_list = observed_overflow_list;
if (cur_overflow_list != BUSY) {
// Do the splice ...
last->set_klass_to_list_ptr(cur_overflow_list);
} else { // cur_overflow_list == BUSY
last->set_klass_to_list_ptr(NULL);
}
observed_overflow_list =
(oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
} while (cur_overflow_list != observed_overflow_list);
}
}
// Push objects on prefix list onto this thread's work queue
assert(prefix != NULL && prefix != BUSY, "program logic");
cur = prefix;
ssize_t n = 0;
while (cur != NULL) {
oop obj_to_push = cur->forwardee();
oop next = oop(cur->klass_or_null());
cur->set_klass(obj_to_push->klass());
// This may be an array object that is self-forwarded. In that case, the list pointer
// space, cur, is not in the Java heap, but rather in the C-heap and should be freed.
if (!is_in_reserved(cur)) {
// This can become a scaling bottleneck when there is work queue overflow coincident
// with promotion failure.
oopDesc* f = cur;
FREE_C_HEAP_ARRAY(oopDesc, f);
} else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {
assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
obj_to_push = cur;
}
bool ok = work_q->push(obj_to_push);
assert(ok, "Should have succeeded");
cur = next;
n++;
}
par_scan_state->note_overflow_refill(n);
#ifndef PRODUCT
assert(_num_par_pushes >= n, "Too many pops?");
Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
#endif
return true;
}
#undef BUSY
void ParNewGeneration::ref_processor_init()
{
if (_ref_processor == NULL) {
// Allocate and initialize a reference processor
_ref_processor = ReferenceProcessor::create_ref_processor(
_reserved, // span
refs_discovery_is_atomic(), // atomic_discovery
refs_discovery_is_mt(), // mt_discovery
NULL, // is_alive_non_header
ParallelGCThreads,
ParallelRefProcEnabled);
}
}
const char* ParNewGeneration::name() const {
return "par new generation";
}