/*
* Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
#include "precompiled.hpp"
#include "classfile/stringTable.hpp"
#include "gc/cms/cmsHeap.inline.hpp"
#include "gc/cms/compactibleFreeListSpace.hpp"
#include "gc/cms/concurrentMarkSweepGeneration.hpp"
#include "gc/cms/parNewGeneration.inline.hpp"
#include "gc/cms/parOopClosures.inline.hpp"
#include "gc/serial/defNewGeneration.inline.hpp"
#include "gc/shared/adaptiveSizePolicy.hpp"
#include "gc/shared/ageTable.inline.hpp"
#include "gc/shared/copyFailedInfo.hpp"
#include "gc/shared/gcHeapSummary.hpp"
#include "gc/shared/gcTimer.hpp"
#include "gc/shared/gcTrace.hpp"
#include "gc/shared/gcTraceTime.inline.hpp"
#include "gc/shared/genOopClosures.inline.hpp"
#include "gc/shared/generation.hpp"
#include "gc/shared/plab.inline.hpp"
#include "gc/shared/preservedMarks.inline.hpp"
#include "gc/shared/referencePolicy.hpp"
#include "gc/shared/referenceProcessorPhaseTimes.hpp"
#include "gc/shared/space.hpp"
#include "gc/shared/spaceDecorator.hpp"
#include "gc/shared/strongRootsScope.hpp"
#include "gc/shared/taskqueue.inline.hpp"
#include "gc/shared/weakProcessor.hpp"
#include "gc/shared/workgroup.hpp"
#include "gc/shared/workerPolicy.hpp"
#include "logging/log.hpp"
#include "logging/logStream.hpp"
#include "memory/iterator.inline.hpp"
#include "memory/resourceArea.hpp"
#include "oops/access.inline.hpp"
#include "oops/compressedOops.inline.hpp"
#include "oops/objArrayOop.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomic.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/java.hpp"
#include "runtime/thread.inline.hpp"
#include "utilities/copy.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/stack.inline.hpp"
ParScanThreadState::ParScanThreadState(Space* to_space_,
ParNewGeneration* young_gen_,
Generation* old_gen_,
int thread_num_,
ObjToScanQueueSet* work_queue_set_,
Stack<oop, mtGC>* overflow_stacks_,
PreservedMarks* preserved_marks_,
size_t desired_plab_sz_,
TaskTerminator& term_) :
_work_queue(work_queue_set_->queue(thread_num_)),
_overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL),
_preserved_marks(preserved_marks_),
_to_space_alloc_buffer(desired_plab_sz_),
_to_space_closure(young_gen_, this),
_old_gen_closure(young_gen_, this),
_to_space_root_closure(young_gen_, this),
_older_gen_closure(young_gen_, this),
_old_gen_root_closure(young_gen_, this),
_evacuate_followers(this, &_to_space_closure, &_old_gen_closure,
&_to_space_root_closure, young_gen_, &_old_gen_root_closure,
work_queue_set_, term_.terminator()),
_is_alive_closure(young_gen_),
_scan_weak_ref_closure(young_gen_, this),
_keep_alive_closure(&_scan_weak_ref_closure),
_to_space(to_space_),
_young_gen(young_gen_),
_old_gen(old_gen_),
_young_old_boundary(NULL),
_thread_num(thread_num_),
_ageTable(false), // false ==> not the global age table, no perf data.
_to_space_full(false),
_strong_roots_time(0.0),
_term_time(0.0)
{
#if TASKQUEUE_STATS
_term_attempts = 0;
_overflow_refills = 0;
_overflow_refill_objs = 0;
#endif // TASKQUEUE_STATS
_survivor_chunk_array = (ChunkArray*) old_gen()->get_data_recorder(thread_num());
_start = os::elapsedTime();
_old_gen_closure.set_generation(old_gen_);
_old_gen_root_closure.set_generation(old_gen_);
}
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(CMSHeap::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");
} 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)) {
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(ParGCUseLocalOverflow, "Else should not call");
assert(young_gen()->overflow_list() == NULL, "Error");
ObjToScanQueue* queue = work_queue();
Stack<oop, mtGC>* const of_stack = overflow_stack();
const size_t num_overflow_elems = of_stack->size();
const size_t space_available = queue->max_elems() - queue->size();
const size_t num_take_elems = MIN3(space_available / 4,
(size_t)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(CMSHeap::heap()->is_in_reserved(cur), "Should be in heap");
assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");
assert(CMSHeap::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(ParGCUseLocalOverflow, "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) {
// If the object is small enough, try to reallocate the buffer.
HeapWord* obj = NULL;
if (!_to_space_full) {
PLAB* 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();
// The minimum size has to be twice SurvivorAlignmentInBytes to
// allow for padding used in the alignment of 1 word. A padding
// of 1 is too small for a filler word so the padding size will
// be increased by SurvivorAlignmentInBytes.
size_t min_usable_size = 2 * static_cast<size_t>(SurvivorAlignmentInBytes >> LogHeapWordSize);
size_t buf_size = MAX2(plab->word_sz(), min_usable_size);
HeapWord* buf_space = sp->par_allocate(buf_size);
if (buf_space == NULL) {
const size_t min_bytes = MAX2(PLAB::min_size(), min_usable_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_buf(buf_space, buf_size);
record_survivor_plab(buf_space, buf_size);
obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes);
// Note that we cannot compare buf_size < word_sz below
// because of AlignmentReserve (see PLAB::allocate()).
assert(obj != NULL || plab->words_remaining() < word_sz,
"Else should have been able to allocate requested object size "
SIZE_FORMAT ", PLAB size " SIZE_FORMAT ", SurvivorAlignmentInBytes "
SIZE_FORMAT ", words_remaining " SIZE_FORMAT,
word_sz, buf_size, SurvivorAlignmentInBytes, plab->words_remaining());
// 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) {
to_space_alloc_buffer()->undo_allocation(obj, word_sz);
}
void ParScanThreadState::print_promotion_failure_size() {
if (_promotion_failed_info.has_failed()) {
log_trace(gc, promotion)(" (%d: promotion failure size = " SIZE_FORMAT ") ",
_thread_num, _promotion_failed_info.first_size());
}
}
class ParScanThreadStateSet: StackObj {
public:
// Initializes states for the specified number of threads;
ParScanThreadStateSet(int num_threads,
Space& to_space,
ParNewGeneration& young_gen,
Generation& old_gen,
ObjToScanQueueSet& queue_set,
Stack<oop, mtGC>* overflow_stacks_,
PreservedMarksSet& preserved_marks_set,
size_t desired_plab_sz,
TaskTerminator& term);
~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); }
inline ParScanThreadState& thread_state(int i);
void trace_promotion_failed(const YoungGCTracer* gc_tracer);
void reset(uint active_workers, bool promotion_failed);
void flush();
#if TASKQUEUE_STATS
static void
print_termination_stats_hdr(outputStream* const st);
void print_termination_stats();
static void
print_taskqueue_stats_hdr(outputStream* const st);
void print_taskqueue_stats();
void reset_stats();
#endif // TASKQUEUE_STATS
private:
TaskTerminator& _term;
ParNewGeneration& _young_gen;
Generation& _old_gen;
ParScanThreadState* _per_thread_states;
const int _num_threads;
public:
bool is_valid(int id) const { return id < _num_threads; }
ParallelTaskTerminator* terminator() { return _term.terminator(); }
};
ParScanThreadStateSet::ParScanThreadStateSet(int num_threads,
Space& to_space,
ParNewGeneration& young_gen,
Generation& old_gen,
ObjToScanQueueSet& queue_set,
Stack<oop, mtGC>* overflow_stacks,
PreservedMarksSet& preserved_marks_set,
size_t desired_plab_sz,
TaskTerminator& term)
: _term(term),
_young_gen(young_gen),
_old_gen(old_gen),
_per_thread_states(NEW_RESOURCE_ARRAY(ParScanThreadState, num_threads)),
_num_threads(num_threads)
{
assert(num_threads > 0, "sanity check!");
assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),
"overflow_stack allocation mismatch");
// Initialize states.
for (int i = 0; i < num_threads; ++i) {
new(_per_thread_states + i)
ParScanThreadState(&to_space, &young_gen, &old_gen, i, &queue_set,
overflow_stacks, preserved_marks_set.get(i),
desired_plab_sz, term);
}
}
inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) {
assert(i >= 0 && i < _num_threads, "sanity check!");
return _per_thread_states[i];
}
void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) {
for (int i = 0; i < _num_threads; ++i) {
if (thread_state(i).promotion_failed()) {
gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info());
thread_state(i).promotion_failed_info().reset();
}
}
}
void ParScanThreadStateSet::reset(uint active_threads, bool promotion_failed) {
_term.terminator()->reset_for_reuse(active_threads);
if (promotion_failed) {
for (int i = 0; i < _num_threads; ++i) {
thread_state(i).print_promotion_failure_size();
}
}
}
#if TASKQUEUE_STATS
void ParScanThreadState::reset_stats() {
taskqueue_stats().reset();
_term_attempts = 0;
_overflow_refills = 0;
_overflow_refill_objs = 0;
}
void ParScanThreadStateSet::reset_stats() {
for (int i = 0; i < _num_threads; ++i) {
thread_state(i).reset_stats();
}
}
void ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) {
st->print_raw_cr("GC Termination Stats");
st->print_raw_cr(" elapsed --strong roots-- -------termination-------");
st->print_raw_cr("thr ms ms % ms % attempts");
st->print_raw_cr("--- --------- --------- ------ --------- ------ --------");
}
void ParScanThreadStateSet::print_termination_stats() {
Log(gc, task, stats) log;
if (!log.is_debug()) {
return;
}
ResourceMark rm;
LogStream ls(log.debug());
outputStream* st = &ls;
print_termination_stats_hdr(st);
for (int i = 0; i < _num_threads; ++i) {
const ParScanThreadState & pss = thread_state(i);
const double elapsed_ms = pss.elapsed_time() * 1000.0;
const double s_roots_ms = pss.strong_roots_time() * 1000.0;
const double term_ms = pss.term_time() * 1000.0;
st->print_cr("%3d %9.2f %9.2f %6.2f %9.2f %6.2f " SIZE_FORMAT_W(8),
i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());
}
}
// Print stats related to work queue activity.
void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) {
st->print_raw_cr("GC Task Stats");
st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
}
void ParScanThreadStateSet::print_taskqueue_stats() {
if (!log_is_enabled(Trace, gc, task, stats)) {
return;
}
Log(gc, task, stats) log;
ResourceMark rm;
LogStream ls(log.trace());
outputStream* st = &ls;
print_taskqueue_stats_hdr(st);
TaskQueueStats totals;
for (int i = 0; i < _num_threads; ++i) {
const ParScanThreadState & pss = thread_state(i);
const TaskQueueStats & stats = pss.taskqueue_stats();
st->print("%3d ", i); stats.print(st); st->cr();
totals += stats;
if (pss.overflow_refills() > 0) {
st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills "
SIZE_FORMAT_W(10) " overflow objects",
pss.overflow_refills(), pss.overflow_refill_objs());
}
}
st->print("tot "); totals.print(st); st->cr();
DEBUG_ONLY(totals.verify());
}
#endif // TASKQUEUE_STATS
void ParScanThreadStateSet::flush() {
// Work in this loop should be kept as lightweight as
// possible since this might otherwise become a bottleneck
// to scaling. Should we add heavy-weight work into this
// loop, consider parallelizing the loop into the worker threads.
for (int i = 0; i < _num_threads; ++i) {
ParScanThreadState& par_scan_state = thread_state(i);
// Flush stats related to To-space PLAB activity and
// retire the last buffer.
par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_young_gen.plab_stats());
// Every thread has its own age table. We need to merge
// them all into one.
AgeTable *local_table = par_scan_state.age_table();
_young_gen.age_table()->merge(local_table);
// Inform old gen that we're done.
_old_gen.par_promote_alloc_done(i);
}
if (UseConcMarkSweepGC) {
// We need to call this even when ResizeOldPLAB is disabled
// so as to avoid breaking some asserts. While we may be able
// to avoid this by reorganizing the code a bit, I am loathe
// to do that unless we find cases where ergo leads to bad
// performance.
CompactibleFreeListSpaceLAB::compute_desired_plab_size();
}
}
ParScanClosure::ParScanClosure(ParNewGeneration* g,
ParScanThreadState* par_scan_state) :
OopsInClassLoaderDataOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) {
_boundary = _g->reserved().end();
}
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)
{}
#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_),
_to_space_root_closure(to_space_root_closure_),
_old_gen_closure(old_gen_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.
if (task_queues()->steal(par_scan_state()->thread_num(),
obj_to_scan)) {
bool res = work_q->push(obj_to_scan);
assert(res, "Empty queue should have room for a 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* young_gen,
Generation* old_gen,
HeapWord* young_old_boundary,
ParScanThreadStateSet* state_set,
StrongRootsScope* strong_roots_scope) :
AbstractGangTask("ParNewGeneration collection"),
_young_gen(young_gen), _old_gen(old_gen),
_young_old_boundary(young_old_boundary),
_state_set(state_set),
_strong_roots_scope(strong_roots_scope)
{}
void ParNewGenTask::work(uint worker_id) {
CMSHeap* heap = CMSHeap::heap();
// Since this is being done in a separate thread, need new resource
// and handle marks.
ResourceMark rm;
HandleMark hm;
ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id);
assert(_state_set->is_valid(worker_id), "Should not have been called");
par_scan_state.set_young_old_boundary(_young_old_boundary);
CLDScanClosure cld_scan_closure(&par_scan_state.to_space_root_closure(),
heap->rem_set()->cld_rem_set()->accumulate_modified_oops());
par_scan_state.start_strong_roots();
heap->young_process_roots(_strong_roots_scope,
&par_scan_state.to_space_root_closure(),
&par_scan_state.older_gen_closure(),
&cld_scan_closure);
par_scan_state.end_strong_roots();
// "evacuate followers".
par_scan_state.evacuate_followers_closure().do_void();
// This will collapse this worker's promoted object list that's
// created during the main ParNew parallel phase of ParNew. This has
// to be called after all workers have finished promoting objects
// and scanning promoted objects. It should be safe calling it from
// here, given that we can only reach here after all thread have
// offered termination, i.e., after there is no more work to be
// done. It will also disable promotion tracking for the rest of
// this GC as it's not necessary to be on during reference processing.
_old_gen->par_oop_since_save_marks_iterate_done((int) worker_id);
}
ParNewGeneration::ParNewGeneration(ReservedSpace rs,
size_t initial_byte_size,
size_t min_byte_size,
size_t max_byte_size)
: DefNewGeneration(rs, initial_byte_size, min_byte_size, max_byte_size, "CMS young collection pauses"),
_plab_stats("Young", YoungPLABSize, PLABWeight),
_overflow_list(NULL),
_is_alive_closure(this)
{
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 i = 0; i < ParallelGCThreads; i++) {
ObjToScanQueue *q = new ObjToScanQueue();
guarantee(q != NULL, "work_queue Allocation failure.");
_task_queues->register_queue(i, q);
}
for (uint i = 0; i < ParallelGCThreads; i++) {
_task_queues->queue(i)->initialize();
}
_overflow_stacks = NULL;
if (ParGCUseLocalOverflow) {
// typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal with ','
typedef Stack<oop, mtGC> GCOopStack;
_overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC);
for (size_t i = 0; i < ParallelGCThreads; ++i) {
new (_overflow_stacks + i) Stack<oop, mtGC>();
}
}
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);
}
}
// ParNewGeneration::
ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
template <class T>
void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
#ifdef ASSERT
{
oop obj = RawAccess<IS_NOT_NULL>::oop_load(p);
// We never expect to see a null reference being processed
// as a weak reference.
assert(oopDesc::is_oop(obj), "expected an oop while scanning weak refs");
}
#endif // ASSERT
Devirtualizer::do_oop_no_verify(_par_cl, p);
if (CMSHeap::heap()->is_in_reserved(p)) {
oop obj = RawAccess<IS_NOT_NULL>::oop_load(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
{
oop obj = RawAccess<IS_NOT_NULL>::oop_load(p);
// We never expect to see a null reference being processed
// as a weak reference.
assert(oopDesc::is_oop(obj), "expected an oop while scanning weak refs");
}
#endif // ASSERT
Devirtualizer::do_oop_no_verify(_cl, p);
if (CMSHeap::heap()->is_in_reserved(p)) {
oop obj = RawAccess<IS_NOT_NULL>::oop_load(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 = RawAccess<>::oop_load(p);
if (!CompressedOops::is_null(heap_oop)) {
oop obj = CompressedOops::decode_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);
RawAccess<IS_NOT_NULL>::oop_store(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& young_gen,
Generation& old_gen,
HeapWord* young_old_boundary,
ParScanThreadStateSet& state_set);
private:
virtual void work(uint worker_id);
private:
ParNewGeneration& _young_gen;
ProcessTask& _task;
Generation& _old_gen;
HeapWord* _young_old_boundary;
ParScanThreadStateSet& _state_set;
};
ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task,
ParNewGeneration& young_gen,
Generation& old_gen,
HeapWord* young_old_boundary,
ParScanThreadStateSet& state_set)
: AbstractGangTask("ParNewGeneration parallel reference processing"),
_young_gen(young_gen),
_task(task),
_old_gen(old_gen),
_young_old_boundary(young_old_boundary),
_state_set(state_set)
{ }
void ParNewRefProcTaskProxy::work(uint worker_id) {
ResourceMark rm;
HandleMark hm;
ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id);
par_scan_state.set_young_old_boundary(_young_old_boundary);
_task.work(worker_id, par_scan_state.is_alive_closure(),
par_scan_state.keep_alive_closure(),
par_scan_state.evacuate_followers_closure());
}
void ParNewRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) {
CMSHeap* gch = CMSHeap::heap();
WorkGang* workers = gch->workers();
assert(workers != NULL, "Need parallel worker threads.");
assert(workers->active_workers() == ergo_workers,
"Ergonomically chosen workers (%u) must be equal to active workers (%u)",
ergo_workers, workers->active_workers());
_state_set.reset(workers->active_workers(), _young_gen.promotion_failed());
ParNewRefProcTaskProxy rp_task(task, _young_gen, _old_gen,
_young_gen.reserved().end(), _state_set);
workers->run_task(&rp_task, workers->active_workers());
_state_set.reset(0 /* bad value in debug if not reset */,
_young_gen.promotion_failed());
}
void ParNewRefProcTaskExecutor::set_single_threaded_mode() {
_state_set.flush();
CMSHeap* heap = CMSHeap::heap();
heap->save_marks();
}
ScanClosureWithParBarrier::
ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
OopsInClassLoaderDataOrGenClosure(g), _g(g), _boundary(g->reserved().end()), _gc_barrier(gc_barrier)
{ }
template <typename OopClosureType1, typename OopClosureType2>
EvacuateFollowersClosureGeneral<OopClosureType1, OopClosureType2>::
EvacuateFollowersClosureGeneral(CMSHeap* heap,
OopClosureType1* cur,
OopClosureType2* older) :
_heap(heap),
_scan_cur_or_nonheap(cur), _scan_older(older)
{ }
template <typename OopClosureType1, typename OopClosureType2>
void EvacuateFollowersClosureGeneral<OopClosureType1, OopClosureType2>::do_void() {
do {
_heap->oop_since_save_marks_iterate(_scan_cur_or_nonheap,
_scan_older);
} while (!_heap->no_allocs_since_save_marks());
}
// A Generation that does parallel young-gen collection.
void ParNewGeneration::handle_promotion_failed(CMSHeap* gch, ParScanThreadStateSet& thread_state_set) {
assert(_promo_failure_scan_stack.is_empty(), "post condition");
_promo_failure_scan_stack.clear(true); // Clear cached segments.
remove_forwarding_pointers();
log_info(gc, promotion)("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_failed();
// Inform the next generation that a promotion failure occurred.
_old_gen->promotion_failure_occurred();
// Trace promotion failure in the parallel GC threads
thread_state_set.trace_promotion_failed(gc_tracer());
// Single threaded code may have reported promotion failure to the global state
if (_promotion_failed_info.has_failed()) {
_gc_tracer.report_promotion_failed(_promotion_failed_info);
}
// Reset the PromotionFailureALot counters.
NOT_PRODUCT(gch->reset_promotion_should_fail();)
}
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");
CMSHeap* gch = CMSHeap::heap();
_gc_timer->register_gc_start();
AdaptiveSizePolicy* size_policy = gch->size_policy();
WorkGang* workers = gch->workers();
assert(workers != NULL, "Need workgang for parallel work");
uint active_workers =
WorkerPolicy::calc_active_workers(workers->total_workers(),
workers->active_workers(),
Threads::number_of_non_daemon_threads());
active_workers = workers->update_active_workers(active_workers);
log_info(gc,task)("Using %u workers of %u for evacuation", active_workers, workers->total_workers());
_old_gen = gch->old_gen();
// If the next generation is too full to accommodate worst-case promotion
// from this generation, pass on collection; let the next generation
// do it.
if (!collection_attempt_is_safe()) {
gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one
return;
}
assert(to()->is_empty(), "Else not collection_attempt_is_safe");
_gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
gch->trace_heap_before_gc(gc_tracer());
init_assuming_no_promotion_failure();
GCTraceTime(Trace, gc, phases) t1("ParNew", NULL, gch->gc_cause());
age_table()->clear();
to()->clear(SpaceDecorator::Mangle);
gch->save_marks();
// Set the correct parallelism (number of queues) in the reference processor
ref_processor()->set_active_mt_degree(active_workers);
// Need to initialize the preserved marks before the ThreadStateSet c'tor.
_preserved_marks_set.init(active_workers);
// Always set the terminator for the active number of workers
// because only those workers go through the termination protocol.
TaskTerminator _term(active_workers, task_queues());
ParScanThreadStateSet thread_state_set(active_workers,
*to(), *this, *_old_gen, *task_queues(),
_overflow_stacks, _preserved_marks_set,
desired_plab_sz(), _term);
thread_state_set.reset(active_workers, promotion_failed());
{
StrongRootsScope srs(active_workers);
ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set, &srs);
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.
// Might multiple workers ever be used? If yes, initialization
// has been done such that the single threaded path should not be used.
if (workers->total_workers() > 1) {
workers->run_task(&tsk);
} else {
tsk.work(0);
}
}
thread_state_set.reset(0 /* Bad value in debug if not reset */,
promotion_failed());
// Trace and reset failed promotion info.
if (promotion_failed()) {
thread_state_set.trace_promotion_failed(gc_tracer());
}
// 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<ScanClosure, ScanClosureWithParBarrier> evacuate_followers(
gch, &scan_without_gc_barrier, &scan_with_gc_barrier);
rp->setup_policy(clear_all_soft_refs);
// Can the mt_degree be set later (at run_task() time would be best)?
rp->set_active_mt_degree(active_workers);
ReferenceProcessorStats stats;
ReferenceProcessorPhaseTimes pt(_gc_timer, rp->max_num_queues());
if (rp->processing_is_mt()) {
ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set);
stats = rp->process_discovered_references(&is_alive, &keep_alive,
&evacuate_followers, &task_executor,
&pt);
} else {
thread_state_set.flush();
gch->save_marks();
stats = rp->process_discovered_references(&is_alive, &keep_alive,
&evacuate_followers, NULL,
&pt);
}
_gc_tracer.report_gc_reference_stats(stats);
_gc_tracer.report_tenuring_threshold(tenuring_threshold());
pt.print_all_references();
assert(gch->no_allocs_since_save_marks(), "evacuation should be done at this point");
WeakProcessor::weak_oops_do(&is_alive, &keep_alive);
// Verify that the usage of keep_alive only forwarded
// the oops and did not find anything new to copy.
assert(gch->no_allocs_since_save_marks(), "unexpectedly copied objects");
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 young collection fails to collect
// sufficient space resizing of the young generation can occur
// and 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();
// A successful scavenge should restart the GC time limit count which is
// for full GC's.
size_policy->reset_gc_overhead_limit_count();
assert(to()->is_empty(), "to space should be empty now");
adjust_desired_tenuring_threshold();
} else {
handle_promotion_failed(gch, thread_state_set);
}
_preserved_marks_set.reclaim();
// 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());
plab_stats()->adjust_desired_plab_sz();
TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats());
TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats());
// We need to use a monotonically non-decreasing time in ms
// or we will see time-warp warnings and os::javaTimeMillis()
// does not guarantee monotonicity.
jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
update_time_of_last_gc(now);
rp->set_enqueuing_is_done(true);
rp->verify_no_references_recorded();
gch->trace_heap_after_gc(gc_tracer());
_gc_timer->register_gc_end();
_gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
}
size_t ParNewGeneration::desired_plab_sz() {
return _plab_stats.desired_plab_sz(CMSHeap::heap()->workers()->active_workers());
}
static int sum;
void ParNewGeneration::waste_some_time() {
for (int i = 0; i < 100; i++) {
sum += i;
}
}
static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(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;
}
// 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(ParScanThreadState* par_scan_state,
oop old,
size_t sz,
markWord 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_raw(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) {
// 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, m);
if (forward_ptr != NULL) {
// someone else beat us to it.
return real_forwardee(old);
}
if (!_promotion_failed) {
new_obj = _old_gen->par_promote(par_scan_state->thread_num(),
old, m, sz);
}
if (new_obj == NULL) {
// promotion failed, forward to self
_promotion_failed = true;
new_obj = old;
par_scan_state->preserved_marks()->push_if_necessary(old, m);
par_scan_state->register_promotion_failure(sz);
}
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);
assert(CMSHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value.");
forward_ptr = old->forward_to_atomic(new_obj, m);
// Restore the mark word copied above.
new_obj->set_mark_raw(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");
// This code must come after the CAS test, or it will print incorrect
// information.
log_develop_trace(gc, scavenge)("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
is_in_reserved(new_obj) ? "copying" : "tenuring",
new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size());
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.
log_develop_trace(gc)("Queue Overflow");
push_on_overflow_list(old, par_scan_state);
TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
}
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;
}
#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 overflows, 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 (cast_to_oop<intptr_t>(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 (ParGCUseLocalOverflow) {
// 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 {
assert(!UseCompressedOops, "Error");
// 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(&_num_par_pushes);
assert(_num_par_pushes > 0, "Tautology");
#endif
if (from_space_obj->forwardee() == from_space_obj) {
oopDesc* listhead = NEW_C_HEAP_OBJ(oopDesc, mtGC);
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 =
Atomic::cmpxchg((oopDesc*)from_space_obj, &_overflow_list, (oopDesc*)cur_overflow_list);
} while (cur_overflow_list != observed_overflow_list);
}
}
bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
bool res;
if (ParGCUseLocalOverflow) {
res = par_scan_state->take_from_overflow_stack();
} else {
assert(!UseCompressedOops, "Error");
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(!UseCompressedOops, "Error");
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 = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
// Trim off a prefix of at most objsFromOverflow items
size_t spin_count = 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/block for a short while...
os::naked_sleep(sleep_time_millis);
if (_overflow_list == NULL) {
// nothing left to take
return false;
} else if (_overflow_list != BUSY) {
// try and grab the prefix
prefix = cast_to_oop(Atomic::xchg((oopDesc*)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((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
}
return false;
}
assert(prefix != NULL && prefix != BUSY, "Error");
oop cur = prefix;
for (size_t i = 1; i < objsFromOverflow; ++i) {
oop next = cur->list_ptr_from_klass();
if (next == NULL) break;
cur = next;
}
assert(cur != NULL, "Loop postcondition");
// Reattach remaining (suffix) to overflow list
oop suffix = cur->list_ptr_from_klass();
if (suffix == 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((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
}
} else {
assert(suffix != BUSY, "Error");
// 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 =
Atomic::cmpxchg((oopDesc*)suffix, &_overflow_list, (oopDesc*)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 (true) {
oop next = last->list_ptr_from_klass();
if (next == NULL) break;
last = next;
}
// 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 =
Atomic::cmpxchg((oopDesc*)suffix, &_overflow_list, (oopDesc*)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 = cur->list_ptr_from_klass();
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_OBJ(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++;
}
TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));
#ifndef PRODUCT
assert(_num_par_pushes >= n, "Too many pops?");
Atomic::sub(n, &_num_par_pushes);
#endif
return true;
}
#undef BUSY
void ParNewGeneration::ref_processor_init() {
if (_ref_processor == NULL) {
// Allocate and initialize a reference processor
_span_based_discoverer.set_span(_reserved);
_ref_processor =
new ReferenceProcessor(&_span_based_discoverer, // span
ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
ParallelGCThreads, // mt processing degree
refs_discovery_is_mt(), // mt discovery
ParallelGCThreads, // mt discovery degree
refs_discovery_is_atomic(), // atomic_discovery
NULL, // is_alive_non_header
false); // disable adjusting number of processing threads
}
}
const char* ParNewGeneration::name() const {
return "par new generation";
}
void ParNewGeneration::restore_preserved_marks() {
SharedRestorePreservedMarksTaskExecutor task_executor(CMSHeap::heap()->workers());
_preserved_marks_set.restore(&task_executor);
}