6484982: G1: process references during evacuation pauses
Summary: G1 now uses two reference processors - one is used by concurrent marking and the other is used by STW GCs (both full and incremental evacuation pauses). In an evacuation pause, the reference processor is embedded into the closures used to scan objects. Doing so causes causes reference objects to be 'discovered' by the reference processor. At the end of the evacuation pause, these discovered reference objects are processed - preserving (and copying) referent objects (and their reachable graphs) as appropriate.
Reviewed-by: ysr, jwilhelm, brutisso, stefank, tonyp
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* 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
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*/
#include "precompiled.hpp"
#include "classfile/symbolTable.hpp"
#include "classfile/systemDictionary.hpp"
#include "classfile/vmSymbols.hpp"
#include "code/icBuffer.hpp"
#include "gc_implementation/shared/collectorCounters.hpp"
#include "gc_implementation/shared/vmGCOperations.hpp"
#include "gc_interface/collectedHeap.inline.hpp"
#include "memory/compactPermGen.hpp"
#include "memory/filemap.hpp"
#include "memory/gcLocker.inline.hpp"
#include "memory/genCollectedHeap.hpp"
#include "memory/genOopClosures.inline.hpp"
#include "memory/generation.inline.hpp"
#include "memory/generationSpec.hpp"
#include "memory/permGen.hpp"
#include "memory/resourceArea.hpp"
#include "memory/sharedHeap.hpp"
#include "memory/space.hpp"
#include "oops/oop.inline.hpp"
#include "oops/oop.inline2.hpp"
#include "runtime/aprofiler.hpp"
#include "runtime/biasedLocking.hpp"
#include "runtime/fprofiler.hpp"
#include "runtime/handles.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/java.hpp"
#include "runtime/vmThread.hpp"
#include "services/memoryService.hpp"
#include "utilities/vmError.hpp"
#include "utilities/workgroup.hpp"
#ifndef SERIALGC
#include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
#include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
#endif
GenCollectedHeap* GenCollectedHeap::_gch;
NOT_PRODUCT(size_t GenCollectedHeap::_skip_header_HeapWords = 0;)
// The set of potentially parallel tasks in strong root scanning.
enum GCH_process_strong_roots_tasks {
// We probably want to parallelize both of these internally, but for now...
GCH_PS_younger_gens,
// Leave this one last.
GCH_PS_NumElements
};
GenCollectedHeap::GenCollectedHeap(GenCollectorPolicy *policy) :
SharedHeap(policy),
_gen_policy(policy),
_gen_process_strong_tasks(new SubTasksDone(GCH_PS_NumElements)),
_full_collections_completed(0)
{
if (_gen_process_strong_tasks == NULL ||
!_gen_process_strong_tasks->valid()) {
vm_exit_during_initialization("Failed necessary allocation.");
}
assert(policy != NULL, "Sanity check");
_preloading_shared_classes = false;
}
jint GenCollectedHeap::initialize() {
CollectedHeap::pre_initialize();
int i;
_n_gens = gen_policy()->number_of_generations();
// While there are no constraints in the GC code that HeapWordSize
// be any particular value, there are multiple other areas in the
// system which believe this to be true (e.g. oop->object_size in some
// cases incorrectly returns the size in wordSize units rather than
// HeapWordSize).
guarantee(HeapWordSize == wordSize, "HeapWordSize must equal wordSize");
// The heap must be at least as aligned as generations.
size_t alignment = Generation::GenGrain;
_gen_specs = gen_policy()->generations();
PermanentGenerationSpec *perm_gen_spec =
collector_policy()->permanent_generation();
// Make sure the sizes are all aligned.
for (i = 0; i < _n_gens; i++) {
_gen_specs[i]->align(alignment);
}
perm_gen_spec->align(alignment);
// If we are dumping the heap, then allocate a wasted block of address
// space in order to push the heap to a lower address. This extra
// address range allows for other (or larger) libraries to be loaded
// without them occupying the space required for the shared spaces.
if (DumpSharedSpaces) {
uintx reserved = 0;
uintx block_size = 64*1024*1024;
while (reserved < SharedDummyBlockSize) {
char* dummy = os::reserve_memory(block_size);
reserved += block_size;
}
}
// Allocate space for the heap.
char* heap_address;
size_t total_reserved = 0;
int n_covered_regions = 0;
ReservedSpace heap_rs(0);
heap_address = allocate(alignment, perm_gen_spec, &total_reserved,
&n_covered_regions, &heap_rs);
if (UseSharedSpaces) {
if (!heap_rs.is_reserved() || heap_address != heap_rs.base()) {
if (heap_rs.is_reserved()) {
heap_rs.release();
}
FileMapInfo* mapinfo = FileMapInfo::current_info();
mapinfo->fail_continue("Unable to reserve shared region.");
allocate(alignment, perm_gen_spec, &total_reserved, &n_covered_regions,
&heap_rs);
}
}
if (!heap_rs.is_reserved()) {
vm_shutdown_during_initialization(
"Could not reserve enough space for object heap");
return JNI_ENOMEM;
}
_reserved = MemRegion((HeapWord*)heap_rs.base(),
(HeapWord*)(heap_rs.base() + heap_rs.size()));
// It is important to do this in a way such that concurrent readers can't
// temporarily think somethings in the heap. (Seen this happen in asserts.)
_reserved.set_word_size(0);
_reserved.set_start((HeapWord*)heap_rs.base());
size_t actual_heap_size = heap_rs.size() - perm_gen_spec->misc_data_size()
- perm_gen_spec->misc_code_size();
_reserved.set_end((HeapWord*)(heap_rs.base() + actual_heap_size));
_rem_set = collector_policy()->create_rem_set(_reserved, n_covered_regions);
set_barrier_set(rem_set()->bs());
_gch = this;
for (i = 0; i < _n_gens; i++) {
ReservedSpace this_rs = heap_rs.first_part(_gen_specs[i]->max_size(),
UseSharedSpaces, UseSharedSpaces);
_gens[i] = _gen_specs[i]->init(this_rs, i, rem_set());
heap_rs = heap_rs.last_part(_gen_specs[i]->max_size());
}
_perm_gen = perm_gen_spec->init(heap_rs, PermSize, rem_set());
clear_incremental_collection_failed();
#ifndef SERIALGC
// If we are running CMS, create the collector responsible
// for collecting the CMS generations.
if (collector_policy()->is_concurrent_mark_sweep_policy()) {
bool success = create_cms_collector();
if (!success) return JNI_ENOMEM;
}
#endif // SERIALGC
return JNI_OK;
}
char* GenCollectedHeap::allocate(size_t alignment,
PermanentGenerationSpec* perm_gen_spec,
size_t* _total_reserved,
int* _n_covered_regions,
ReservedSpace* heap_rs){
const char overflow_msg[] = "The size of the object heap + VM data exceeds "
"the maximum representable size";
// Now figure out the total size.
size_t total_reserved = 0;
int n_covered_regions = 0;
const size_t pageSize = UseLargePages ?
os::large_page_size() : os::vm_page_size();
for (int i = 0; i < _n_gens; i++) {
total_reserved += _gen_specs[i]->max_size();
if (total_reserved < _gen_specs[i]->max_size()) {
vm_exit_during_initialization(overflow_msg);
}
n_covered_regions += _gen_specs[i]->n_covered_regions();
}
assert(total_reserved % pageSize == 0,
err_msg("Gen size; total_reserved=" SIZE_FORMAT ", pageSize="
SIZE_FORMAT, total_reserved, pageSize));
total_reserved += perm_gen_spec->max_size();
assert(total_reserved % pageSize == 0,
err_msg("Perm size; total_reserved=" SIZE_FORMAT ", pageSize="
SIZE_FORMAT ", perm gen max=" SIZE_FORMAT, total_reserved,
pageSize, perm_gen_spec->max_size()));
if (total_reserved < perm_gen_spec->max_size()) {
vm_exit_during_initialization(overflow_msg);
}
n_covered_regions += perm_gen_spec->n_covered_regions();
// Add the size of the data area which shares the same reserved area
// as the heap, but which is not actually part of the heap.
size_t s = perm_gen_spec->misc_data_size() + perm_gen_spec->misc_code_size();
total_reserved += s;
if (total_reserved < s) {
vm_exit_during_initialization(overflow_msg);
}
if (UseLargePages) {
assert(total_reserved != 0, "total_reserved cannot be 0");
total_reserved = round_to(total_reserved, os::large_page_size());
if (total_reserved < os::large_page_size()) {
vm_exit_during_initialization(overflow_msg);
}
}
// Calculate the address at which the heap must reside in order for
// the shared data to be at the required address.
char* heap_address;
if (UseSharedSpaces) {
// Calculate the address of the first word beyond the heap.
FileMapInfo* mapinfo = FileMapInfo::current_info();
int lr = CompactingPermGenGen::n_regions - 1;
size_t capacity = align_size_up(mapinfo->space_capacity(lr), alignment);
heap_address = mapinfo->region_base(lr) + capacity;
// Calculate the address of the first word of the heap.
heap_address -= total_reserved;
} else {
heap_address = NULL; // any address will do.
if (UseCompressedOops) {
heap_address = Universe::preferred_heap_base(total_reserved, Universe::UnscaledNarrowOop);
*_total_reserved = total_reserved;
*_n_covered_regions = n_covered_regions;
*heap_rs = ReservedHeapSpace(total_reserved, alignment,
UseLargePages, heap_address);
if (heap_address != NULL && !heap_rs->is_reserved()) {
// Failed to reserve at specified address - the requested memory
// region is taken already, for example, by 'java' launcher.
// Try again to reserver heap higher.
heap_address = Universe::preferred_heap_base(total_reserved, Universe::ZeroBasedNarrowOop);
*heap_rs = ReservedHeapSpace(total_reserved, alignment,
UseLargePages, heap_address);
if (heap_address != NULL && !heap_rs->is_reserved()) {
// Failed to reserve at specified address again - give up.
heap_address = Universe::preferred_heap_base(total_reserved, Universe::HeapBasedNarrowOop);
assert(heap_address == NULL, "");
*heap_rs = ReservedHeapSpace(total_reserved, alignment,
UseLargePages, heap_address);
}
}
return heap_address;
}
}
*_total_reserved = total_reserved;
*_n_covered_regions = n_covered_regions;
*heap_rs = ReservedHeapSpace(total_reserved, alignment,
UseLargePages, heap_address);
return heap_address;
}
void GenCollectedHeap::post_initialize() {
SharedHeap::post_initialize();
TwoGenerationCollectorPolicy *policy =
(TwoGenerationCollectorPolicy *)collector_policy();
guarantee(policy->is_two_generation_policy(), "Illegal policy type");
DefNewGeneration* def_new_gen = (DefNewGeneration*) get_gen(0);
assert(def_new_gen->kind() == Generation::DefNew ||
def_new_gen->kind() == Generation::ParNew ||
def_new_gen->kind() == Generation::ASParNew,
"Wrong generation kind");
Generation* old_gen = get_gen(1);
assert(old_gen->kind() == Generation::ConcurrentMarkSweep ||
old_gen->kind() == Generation::ASConcurrentMarkSweep ||
old_gen->kind() == Generation::MarkSweepCompact,
"Wrong generation kind");
policy->initialize_size_policy(def_new_gen->eden()->capacity(),
old_gen->capacity(),
def_new_gen->from()->capacity());
policy->initialize_gc_policy_counters();
}
void GenCollectedHeap::ref_processing_init() {
SharedHeap::ref_processing_init();
for (int i = 0; i < _n_gens; i++) {
_gens[i]->ref_processor_init();
}
}
size_t GenCollectedHeap::capacity() const {
size_t res = 0;
for (int i = 0; i < _n_gens; i++) {
res += _gens[i]->capacity();
}
return res;
}
size_t GenCollectedHeap::used() const {
size_t res = 0;
for (int i = 0; i < _n_gens; i++) {
res += _gens[i]->used();
}
return res;
}
// Save the "used_region" for generations level and lower,
// and, if perm is true, for perm gen.
void GenCollectedHeap::save_used_regions(int level, bool perm) {
assert(level < _n_gens, "Illegal level parameter");
for (int i = level; i >= 0; i--) {
_gens[i]->save_used_region();
}
if (perm) {
perm_gen()->save_used_region();
}
}
size_t GenCollectedHeap::max_capacity() const {
size_t res = 0;
for (int i = 0; i < _n_gens; i++) {
res += _gens[i]->max_capacity();
}
return res;
}
// Update the _full_collections_completed counter
// at the end of a stop-world full GC.
unsigned int GenCollectedHeap::update_full_collections_completed() {
MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
assert(_full_collections_completed <= _total_full_collections,
"Can't complete more collections than were started");
_full_collections_completed = _total_full_collections;
ml.notify_all();
return _full_collections_completed;
}
// Update the _full_collections_completed counter, as appropriate,
// at the end of a concurrent GC cycle. Note the conditional update
// below to allow this method to be called by a concurrent collector
// without synchronizing in any manner with the VM thread (which
// may already have initiated a STW full collection "concurrently").
unsigned int GenCollectedHeap::update_full_collections_completed(unsigned int count) {
MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
assert((_full_collections_completed <= _total_full_collections) &&
(count <= _total_full_collections),
"Can't complete more collections than were started");
if (count > _full_collections_completed) {
_full_collections_completed = count;
ml.notify_all();
}
return _full_collections_completed;
}
#ifndef PRODUCT
// Override of memory state checking method in CollectedHeap:
// Some collectors (CMS for example) can't have badHeapWordVal written
// in the first two words of an object. (For instance , in the case of
// CMS these words hold state used to synchronize between certain
// (concurrent) GC steps and direct allocating mutators.)
// The skip_header_HeapWords() method below, allows us to skip
// over the requisite number of HeapWord's. Note that (for
// generational collectors) this means that those many words are
// skipped in each object, irrespective of the generation in which
// that object lives. The resultant loss of precision seems to be
// harmless and the pain of avoiding that imprecision appears somewhat
// higher than we are prepared to pay for such rudimentary debugging
// support.
void GenCollectedHeap::check_for_non_bad_heap_word_value(HeapWord* addr,
size_t size) {
if (CheckMemoryInitialization && ZapUnusedHeapArea) {
// We are asked to check a size in HeapWords,
// but the memory is mangled in juint words.
juint* start = (juint*) (addr + skip_header_HeapWords());
juint* end = (juint*) (addr + size);
for (juint* slot = start; slot < end; slot += 1) {
assert(*slot == badHeapWordVal,
"Found non badHeapWordValue in pre-allocation check");
}
}
}
#endif
HeapWord* GenCollectedHeap::attempt_allocation(size_t size,
bool is_tlab,
bool first_only) {
HeapWord* res;
for (int i = 0; i < _n_gens; i++) {
if (_gens[i]->should_allocate(size, is_tlab)) {
res = _gens[i]->allocate(size, is_tlab);
if (res != NULL) return res;
else if (first_only) break;
}
}
// Otherwise...
return NULL;
}
HeapWord* GenCollectedHeap::mem_allocate(size_t size,
bool* gc_overhead_limit_was_exceeded) {
return collector_policy()->mem_allocate_work(size,
false /* is_tlab */,
gc_overhead_limit_was_exceeded);
}
bool GenCollectedHeap::must_clear_all_soft_refs() {
return _gc_cause == GCCause::_last_ditch_collection;
}
bool GenCollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) {
return UseConcMarkSweepGC &&
((cause == GCCause::_gc_locker && GCLockerInvokesConcurrent) ||
(cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent));
}
void GenCollectedHeap::do_collection(bool full,
bool clear_all_soft_refs,
size_t size,
bool is_tlab,
int max_level) {
bool prepared_for_verification = false;
ResourceMark rm;
DEBUG_ONLY(Thread* my_thread = Thread::current();)
assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
assert(my_thread->is_VM_thread() ||
my_thread->is_ConcurrentGC_thread(),
"incorrect thread type capability");
assert(Heap_lock->is_locked(),
"the requesting thread should have the Heap_lock");
guarantee(!is_gc_active(), "collection is not reentrant");
assert(max_level < n_gens(), "sanity check");
if (GC_locker::check_active_before_gc()) {
return; // GC is disabled (e.g. JNI GetXXXCritical operation)
}
const bool do_clear_all_soft_refs = clear_all_soft_refs ||
collector_policy()->should_clear_all_soft_refs();
ClearedAllSoftRefs casr(do_clear_all_soft_refs, collector_policy());
const size_t perm_prev_used = perm_gen()->used();
if (PrintHeapAtGC) {
Universe::print_heap_before_gc();
if (Verbose) {
gclog_or_tty->print_cr("GC Cause: %s", GCCause::to_string(gc_cause()));
}
}
{
FlagSetting fl(_is_gc_active, true);
bool complete = full && (max_level == (n_gens()-1));
const char* gc_cause_str = "GC ";
if (complete) {
GCCause::Cause cause = gc_cause();
if (cause == GCCause::_java_lang_system_gc) {
gc_cause_str = "Full GC (System) ";
} else {
gc_cause_str = "Full GC ";
}
}
gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
TraceTime t(gc_cause_str, PrintGCDetails, false, gclog_or_tty);
gc_prologue(complete);
increment_total_collections(complete);
size_t gch_prev_used = used();
int starting_level = 0;
if (full) {
// Search for the oldest generation which will collect all younger
// generations, and start collection loop there.
for (int i = max_level; i >= 0; i--) {
if (_gens[i]->full_collects_younger_generations()) {
starting_level = i;
break;
}
}
}
bool must_restore_marks_for_biased_locking = false;
int max_level_collected = starting_level;
for (int i = starting_level; i <= max_level; i++) {
if (_gens[i]->should_collect(full, size, is_tlab)) {
if (i == n_gens() - 1) { // a major collection is to happen
if (!complete) {
// The full_collections increment was missed above.
increment_total_full_collections();
}
pre_full_gc_dump(); // do any pre full gc dumps
}
// Timer for individual generations. Last argument is false: no CR
TraceTime t1(_gens[i]->short_name(), PrintGCDetails, false, gclog_or_tty);
TraceCollectorStats tcs(_gens[i]->counters());
TraceMemoryManagerStats tmms(_gens[i]->kind(),gc_cause());
size_t prev_used = _gens[i]->used();
_gens[i]->stat_record()->invocations++;
_gens[i]->stat_record()->accumulated_time.start();
// Must be done anew before each collection because
// a previous collection will do mangling and will
// change top of some spaces.
record_gen_tops_before_GC();
if (PrintGC && Verbose) {
gclog_or_tty->print("level=%d invoke=%d size=" SIZE_FORMAT,
i,
_gens[i]->stat_record()->invocations,
size*HeapWordSize);
}
if (VerifyBeforeGC && i >= VerifyGCLevel &&
total_collections() >= VerifyGCStartAt) {
HandleMark hm; // Discard invalid handles created during verification
if (!prepared_for_verification) {
prepare_for_verify();
prepared_for_verification = true;
}
gclog_or_tty->print(" VerifyBeforeGC:");
Universe::verify(true);
}
COMPILER2_PRESENT(DerivedPointerTable::clear());
if (!must_restore_marks_for_biased_locking &&
_gens[i]->performs_in_place_marking()) {
// We perform this mark word preservation work lazily
// because it's only at this point that we know whether we
// absolutely have to do it; we want to avoid doing it for
// scavenge-only collections where it's unnecessary
must_restore_marks_for_biased_locking = true;
BiasedLocking::preserve_marks();
}
// Do collection work
{
// Note on ref discovery: For what appear to be historical reasons,
// GCH enables and disabled (by enqueing) refs discovery.
// In the future this should be moved into the generation's
// collect method so that ref discovery and enqueueing concerns
// are local to a generation. The collect method could return
// an appropriate indication in the case that notification on
// the ref lock was needed. This will make the treatment of
// weak refs more uniform (and indeed remove such concerns
// from GCH). XXX
HandleMark hm; // Discard invalid handles created during gc
save_marks(); // save marks for all gens
// We want to discover references, but not process them yet.
// This mode is disabled in process_discovered_references if the
// generation does some collection work, or in
// enqueue_discovered_references if the generation returns
// without doing any work.
ReferenceProcessor* rp = _gens[i]->ref_processor();
// If the discovery of ("weak") refs in this generation is
// atomic wrt other collectors in this configuration, we
// are guaranteed to have empty discovered ref lists.
if (rp->discovery_is_atomic()) {
rp->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/);
rp->setup_policy(do_clear_all_soft_refs);
} else {
// collect() below will enable discovery as appropriate
}
_gens[i]->collect(full, do_clear_all_soft_refs, size, is_tlab);
if (!rp->enqueuing_is_done()) {
rp->enqueue_discovered_references();
} else {
rp->set_enqueuing_is_done(false);
}
rp->verify_no_references_recorded();
}
max_level_collected = i;
// Determine if allocation request was met.
if (size > 0) {
if (!is_tlab || _gens[i]->supports_tlab_allocation()) {
if (size*HeapWordSize <= _gens[i]->unsafe_max_alloc_nogc()) {
size = 0;
}
}
}
COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
_gens[i]->stat_record()->accumulated_time.stop();
update_gc_stats(i, full);
if (VerifyAfterGC && i >= VerifyGCLevel &&
total_collections() >= VerifyGCStartAt) {
HandleMark hm; // Discard invalid handles created during verification
gclog_or_tty->print(" VerifyAfterGC:");
Universe::verify(false);
}
if (PrintGCDetails) {
gclog_or_tty->print(":");
_gens[i]->print_heap_change(prev_used);
}
}
}
// Update "complete" boolean wrt what actually transpired --
// for instance, a promotion failure could have led to
// a whole heap collection.
complete = complete || (max_level_collected == n_gens() - 1);
if (complete) { // We did a "major" collection
post_full_gc_dump(); // do any post full gc dumps
}
if (PrintGCDetails) {
print_heap_change(gch_prev_used);
// Print perm gen info for full GC with PrintGCDetails flag.
if (complete) {
print_perm_heap_change(perm_prev_used);
}
}
for (int j = max_level_collected; j >= 0; j -= 1) {
// Adjust generation sizes.
_gens[j]->compute_new_size();
}
if (complete) {
// Ask the permanent generation to adjust size for full collections
perm()->compute_new_size();
update_full_collections_completed();
}
// Track memory usage and detect low memory after GC finishes
MemoryService::track_memory_usage();
gc_epilogue(complete);
if (must_restore_marks_for_biased_locking) {
BiasedLocking::restore_marks();
}
}
AdaptiveSizePolicy* sp = gen_policy()->size_policy();
AdaptiveSizePolicyOutput(sp, total_collections());
if (PrintHeapAtGC) {
Universe::print_heap_after_gc();
}
#ifdef TRACESPINNING
ParallelTaskTerminator::print_termination_counts();
#endif
if (ExitAfterGCNum > 0 && total_collections() == ExitAfterGCNum) {
tty->print_cr("Stopping after GC #%d", ExitAfterGCNum);
vm_exit(-1);
}
}
HeapWord* GenCollectedHeap::satisfy_failed_allocation(size_t size, bool is_tlab) {
return collector_policy()->satisfy_failed_allocation(size, is_tlab);
}
void GenCollectedHeap::set_par_threads(int t) {
SharedHeap::set_par_threads(t);
_gen_process_strong_tasks->set_n_threads(t);
}
void GenCollectedHeap::
gen_process_strong_roots(int level,
bool younger_gens_as_roots,
bool activate_scope,
bool collecting_perm_gen,
SharedHeap::ScanningOption so,
OopsInGenClosure* not_older_gens,
bool do_code_roots,
OopsInGenClosure* older_gens) {
// General strong roots.
if (!do_code_roots) {
SharedHeap::process_strong_roots(activate_scope, collecting_perm_gen, so,
not_older_gens, NULL, older_gens);
} else {
bool do_code_marking = (activate_scope || nmethod::oops_do_marking_is_active());
CodeBlobToOopClosure code_roots(not_older_gens, /*do_marking=*/ do_code_marking);
SharedHeap::process_strong_roots(activate_scope, collecting_perm_gen, so,
not_older_gens, &code_roots, older_gens);
}
if (younger_gens_as_roots) {
if (!_gen_process_strong_tasks->is_task_claimed(GCH_PS_younger_gens)) {
for (int i = 0; i < level; i++) {
not_older_gens->set_generation(_gens[i]);
_gens[i]->oop_iterate(not_older_gens);
}
not_older_gens->reset_generation();
}
}
// When collection is parallel, all threads get to cooperate to do
// older-gen scanning.
for (int i = level+1; i < _n_gens; i++) {
older_gens->set_generation(_gens[i]);
rem_set()->younger_refs_iterate(_gens[i], older_gens);
older_gens->reset_generation();
}
_gen_process_strong_tasks->all_tasks_completed();
}
void GenCollectedHeap::gen_process_weak_roots(OopClosure* root_closure,
CodeBlobClosure* code_roots,
OopClosure* non_root_closure) {
SharedHeap::process_weak_roots(root_closure, code_roots, non_root_closure);
// "Local" "weak" refs
for (int i = 0; i < _n_gens; i++) {
_gens[i]->ref_processor()->weak_oops_do(root_closure);
}
}
#define GCH_SINCE_SAVE_MARKS_ITERATE_DEFN(OopClosureType, nv_suffix) \
void GenCollectedHeap:: \
oop_since_save_marks_iterate(int level, \
OopClosureType* cur, \
OopClosureType* older) { \
_gens[level]->oop_since_save_marks_iterate##nv_suffix(cur); \
for (int i = level+1; i < n_gens(); i++) { \
_gens[i]->oop_since_save_marks_iterate##nv_suffix(older); \
} \
perm_gen()->oop_since_save_marks_iterate##nv_suffix(older); \
}
ALL_SINCE_SAVE_MARKS_CLOSURES(GCH_SINCE_SAVE_MARKS_ITERATE_DEFN)
#undef GCH_SINCE_SAVE_MARKS_ITERATE_DEFN
bool GenCollectedHeap::no_allocs_since_save_marks(int level) {
for (int i = level; i < _n_gens; i++) {
if (!_gens[i]->no_allocs_since_save_marks()) return false;
}
return perm_gen()->no_allocs_since_save_marks();
}
bool GenCollectedHeap::supports_inline_contig_alloc() const {
return _gens[0]->supports_inline_contig_alloc();
}
HeapWord** GenCollectedHeap::top_addr() const {
return _gens[0]->top_addr();
}
HeapWord** GenCollectedHeap::end_addr() const {
return _gens[0]->end_addr();
}
size_t GenCollectedHeap::unsafe_max_alloc() {
return _gens[0]->unsafe_max_alloc_nogc();
}
// public collection interfaces
void GenCollectedHeap::collect(GCCause::Cause cause) {
if (should_do_concurrent_full_gc(cause)) {
#ifndef SERIALGC
// mostly concurrent full collection
collect_mostly_concurrent(cause);
#else // SERIALGC
ShouldNotReachHere();
#endif // SERIALGC
} else {
#ifdef ASSERT
if (cause == GCCause::_scavenge_alot) {
// minor collection only
collect(cause, 0);
} else {
// Stop-the-world full collection
collect(cause, n_gens() - 1);
}
#else
// Stop-the-world full collection
collect(cause, n_gens() - 1);
#endif
}
}
void GenCollectedHeap::collect(GCCause::Cause cause, int max_level) {
// The caller doesn't have the Heap_lock
assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock");
MutexLocker ml(Heap_lock);
collect_locked(cause, max_level);
}
// This interface assumes that it's being called by the
// vm thread. It collects the heap assuming that the
// heap lock is already held and that we are executing in
// the context of the vm thread.
void GenCollectedHeap::collect_as_vm_thread(GCCause::Cause cause) {
assert(Thread::current()->is_VM_thread(), "Precondition#1");
assert(Heap_lock->is_locked(), "Precondition#2");
GCCauseSetter gcs(this, cause);
switch (cause) {
case GCCause::_heap_inspection:
case GCCause::_heap_dump: {
HandleMark hm;
do_full_collection(false, // don't clear all soft refs
n_gens() - 1);
break;
}
default: // XXX FIX ME
ShouldNotReachHere(); // Unexpected use of this function
}
}
void GenCollectedHeap::collect_locked(GCCause::Cause cause) {
// The caller has the Heap_lock
assert(Heap_lock->owned_by_self(), "this thread should own the Heap_lock");
collect_locked(cause, n_gens() - 1);
}
// this is the private collection interface
// The Heap_lock is expected to be held on entry.
void GenCollectedHeap::collect_locked(GCCause::Cause cause, int max_level) {
if (_preloading_shared_classes) {
report_out_of_shared_space(SharedPermGen);
}
// Read the GC count while holding the Heap_lock
unsigned int gc_count_before = total_collections();
unsigned int full_gc_count_before = total_full_collections();
{
MutexUnlocker mu(Heap_lock); // give up heap lock, execute gets it back
VM_GenCollectFull op(gc_count_before, full_gc_count_before,
cause, max_level);
VMThread::execute(&op);
}
}
#ifndef SERIALGC
bool GenCollectedHeap::create_cms_collector() {
assert(((_gens[1]->kind() == Generation::ConcurrentMarkSweep) ||
(_gens[1]->kind() == Generation::ASConcurrentMarkSweep)) &&
_perm_gen->as_gen()->kind() == Generation::ConcurrentMarkSweep,
"Unexpected generation kinds");
// Skip two header words in the block content verification
NOT_PRODUCT(_skip_header_HeapWords = CMSCollector::skip_header_HeapWords();)
CMSCollector* collector = new CMSCollector(
(ConcurrentMarkSweepGeneration*)_gens[1],
(ConcurrentMarkSweepGeneration*)_perm_gen->as_gen(),
_rem_set->as_CardTableRS(),
(ConcurrentMarkSweepPolicy*) collector_policy());
if (collector == NULL || !collector->completed_initialization()) {
if (collector) {
delete collector; // Be nice in embedded situation
}
vm_shutdown_during_initialization("Could not create CMS collector");
return false;
}
return true; // success
}
void GenCollectedHeap::collect_mostly_concurrent(GCCause::Cause cause) {
assert(!Heap_lock->owned_by_self(), "Should not own Heap_lock");
MutexLocker ml(Heap_lock);
// Read the GC counts while holding the Heap_lock
unsigned int full_gc_count_before = total_full_collections();
unsigned int gc_count_before = total_collections();
{
MutexUnlocker mu(Heap_lock);
VM_GenCollectFullConcurrent op(gc_count_before, full_gc_count_before, cause);
VMThread::execute(&op);
}
}
#endif // SERIALGC
void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs,
int max_level) {
int local_max_level;
if (!incremental_collection_will_fail(false /* don't consult_young */) &&
gc_cause() == GCCause::_gc_locker) {
local_max_level = 0;
} else {
local_max_level = max_level;
}
do_collection(true /* full */,
clear_all_soft_refs /* clear_all_soft_refs */,
0 /* size */,
false /* is_tlab */,
local_max_level /* max_level */);
// Hack XXX FIX ME !!!
// A scavenge may not have been attempted, or may have
// been attempted and failed, because the old gen was too full
if (local_max_level == 0 && gc_cause() == GCCause::_gc_locker &&
incremental_collection_will_fail(false /* don't consult_young */)) {
if (PrintGCDetails) {
gclog_or_tty->print_cr("GC locker: Trying a full collection "
"because scavenge failed");
}
// This time allow the old gen to be collected as well
do_collection(true /* full */,
clear_all_soft_refs /* clear_all_soft_refs */,
0 /* size */,
false /* is_tlab */,
n_gens() - 1 /* max_level */);
}
}
bool GenCollectedHeap::is_in_young(oop p) {
bool result = ((HeapWord*)p) < _gens[_n_gens - 1]->reserved().start();
assert(result == _gens[0]->is_in_reserved(p),
err_msg("incorrect test - result=%d, p=" PTR_FORMAT, result, (void*)p));
return result;
}
// Returns "TRUE" iff "p" points into the allocated area of the heap.
bool GenCollectedHeap::is_in(const void* p) const {
#ifndef ASSERT
guarantee(VerifyBeforeGC ||
VerifyDuringGC ||
VerifyBeforeExit ||
PrintAssembly ||
tty->count() != 0 || // already printing
VerifyAfterGC ||
VMError::fatal_error_in_progress(), "too expensive");
#endif
// This might be sped up with a cache of the last generation that
// answered yes.
for (int i = 0; i < _n_gens; i++) {
if (_gens[i]->is_in(p)) return true;
}
if (_perm_gen->as_gen()->is_in(p)) return true;
// Otherwise...
return false;
}
#ifdef ASSERT
// Don't implement this by using is_in_young(). This method is used
// in some cases to check that is_in_young() is correct.
bool GenCollectedHeap::is_in_partial_collection(const void* p) {
assert(is_in_reserved(p) || p == NULL,
"Does not work if address is non-null and outside of the heap");
// The order of the generations is young (low addr), old, perm (high addr)
return p < _gens[_n_gens - 2]->reserved().end() && p != NULL;
}
#endif
void GenCollectedHeap::oop_iterate(OopClosure* cl) {
for (int i = 0; i < _n_gens; i++) {
_gens[i]->oop_iterate(cl);
}
}
void GenCollectedHeap::oop_iterate(MemRegion mr, OopClosure* cl) {
for (int i = 0; i < _n_gens; i++) {
_gens[i]->oop_iterate(mr, cl);
}
}
void GenCollectedHeap::object_iterate(ObjectClosure* cl) {
for (int i = 0; i < _n_gens; i++) {
_gens[i]->object_iterate(cl);
}
perm_gen()->object_iterate(cl);
}
void GenCollectedHeap::safe_object_iterate(ObjectClosure* cl) {
for (int i = 0; i < _n_gens; i++) {
_gens[i]->safe_object_iterate(cl);
}
perm_gen()->safe_object_iterate(cl);
}
void GenCollectedHeap::object_iterate_since_last_GC(ObjectClosure* cl) {
for (int i = 0; i < _n_gens; i++) {
_gens[i]->object_iterate_since_last_GC(cl);
}
}
Space* GenCollectedHeap::space_containing(const void* addr) const {
for (int i = 0; i < _n_gens; i++) {
Space* res = _gens[i]->space_containing(addr);
if (res != NULL) return res;
}
Space* res = perm_gen()->space_containing(addr);
if (res != NULL) return res;
// Otherwise...
assert(false, "Could not find containing space");
return NULL;
}
HeapWord* GenCollectedHeap::block_start(const void* addr) const {
assert(is_in_reserved(addr), "block_start of address outside of heap");
for (int i = 0; i < _n_gens; i++) {
if (_gens[i]->is_in_reserved(addr)) {
assert(_gens[i]->is_in(addr),
"addr should be in allocated part of generation");
return _gens[i]->block_start(addr);
}
}
if (perm_gen()->is_in_reserved(addr)) {
assert(perm_gen()->is_in(addr),
"addr should be in allocated part of perm gen");
return perm_gen()->block_start(addr);
}
assert(false, "Some generation should contain the address");
return NULL;
}
size_t GenCollectedHeap::block_size(const HeapWord* addr) const {
assert(is_in_reserved(addr), "block_size of address outside of heap");
for (int i = 0; i < _n_gens; i++) {
if (_gens[i]->is_in_reserved(addr)) {
assert(_gens[i]->is_in(addr),
"addr should be in allocated part of generation");
return _gens[i]->block_size(addr);
}
}
if (perm_gen()->is_in_reserved(addr)) {
assert(perm_gen()->is_in(addr),
"addr should be in allocated part of perm gen");
return perm_gen()->block_size(addr);
}
assert(false, "Some generation should contain the address");
return 0;
}
bool GenCollectedHeap::block_is_obj(const HeapWord* addr) const {
assert(is_in_reserved(addr), "block_is_obj of address outside of heap");
assert(block_start(addr) == addr, "addr must be a block start");
for (int i = 0; i < _n_gens; i++) {
if (_gens[i]->is_in_reserved(addr)) {
return _gens[i]->block_is_obj(addr);
}
}
if (perm_gen()->is_in_reserved(addr)) {
return perm_gen()->block_is_obj(addr);
}
assert(false, "Some generation should contain the address");
return false;
}
bool GenCollectedHeap::supports_tlab_allocation() const {
for (int i = 0; i < _n_gens; i += 1) {
if (_gens[i]->supports_tlab_allocation()) {
return true;
}
}
return false;
}
size_t GenCollectedHeap::tlab_capacity(Thread* thr) const {
size_t result = 0;
for (int i = 0; i < _n_gens; i += 1) {
if (_gens[i]->supports_tlab_allocation()) {
result += _gens[i]->tlab_capacity();
}
}
return result;
}
size_t GenCollectedHeap::unsafe_max_tlab_alloc(Thread* thr) const {
size_t result = 0;
for (int i = 0; i < _n_gens; i += 1) {
if (_gens[i]->supports_tlab_allocation()) {
result += _gens[i]->unsafe_max_tlab_alloc();
}
}
return result;
}
HeapWord* GenCollectedHeap::allocate_new_tlab(size_t size) {
bool gc_overhead_limit_was_exceeded;
return collector_policy()->mem_allocate_work(size /* size */,
true /* is_tlab */,
&gc_overhead_limit_was_exceeded);
}
// Requires "*prev_ptr" to be non-NULL. Deletes and a block of minimal size
// from the list headed by "*prev_ptr".
static ScratchBlock *removeSmallestScratch(ScratchBlock **prev_ptr) {
bool first = true;
size_t min_size = 0; // "first" makes this conceptually infinite.
ScratchBlock **smallest_ptr, *smallest;
ScratchBlock *cur = *prev_ptr;
while (cur) {
assert(*prev_ptr == cur, "just checking");
if (first || cur->num_words < min_size) {
smallest_ptr = prev_ptr;
smallest = cur;
min_size = smallest->num_words;
first = false;
}
prev_ptr = &cur->next;
cur = cur->next;
}
smallest = *smallest_ptr;
*smallest_ptr = smallest->next;
return smallest;
}
// Sort the scratch block list headed by res into decreasing size order,
// and set "res" to the result.
static void sort_scratch_list(ScratchBlock*& list) {
ScratchBlock* sorted = NULL;
ScratchBlock* unsorted = list;
while (unsorted) {
ScratchBlock *smallest = removeSmallestScratch(&unsorted);
smallest->next = sorted;
sorted = smallest;
}
list = sorted;
}
ScratchBlock* GenCollectedHeap::gather_scratch(Generation* requestor,
size_t max_alloc_words) {
ScratchBlock* res = NULL;
for (int i = 0; i < _n_gens; i++) {
_gens[i]->contribute_scratch(res, requestor, max_alloc_words);
}
sort_scratch_list(res);
return res;
}
void GenCollectedHeap::release_scratch() {
for (int i = 0; i < _n_gens; i++) {
_gens[i]->reset_scratch();
}
}
class GenPrepareForVerifyClosure: public GenCollectedHeap::GenClosure {
void do_generation(Generation* gen) {
gen->prepare_for_verify();
}
};
void GenCollectedHeap::prepare_for_verify() {
ensure_parsability(false); // no need to retire TLABs
GenPrepareForVerifyClosure blk;
generation_iterate(&blk, false);
perm_gen()->prepare_for_verify();
}
void GenCollectedHeap::generation_iterate(GenClosure* cl,
bool old_to_young) {
if (old_to_young) {
for (int i = _n_gens-1; i >= 0; i--) {
cl->do_generation(_gens[i]);
}
} else {
for (int i = 0; i < _n_gens; i++) {
cl->do_generation(_gens[i]);
}
}
}
void GenCollectedHeap::space_iterate(SpaceClosure* cl) {
for (int i = 0; i < _n_gens; i++) {
_gens[i]->space_iterate(cl, true);
}
perm_gen()->space_iterate(cl, true);
}
bool GenCollectedHeap::is_maximal_no_gc() const {
for (int i = 0; i < _n_gens; i++) { // skip perm gen
if (!_gens[i]->is_maximal_no_gc()) {
return false;
}
}
return true;
}
void GenCollectedHeap::save_marks() {
for (int i = 0; i < _n_gens; i++) {
_gens[i]->save_marks();
}
perm_gen()->save_marks();
}
void GenCollectedHeap::compute_new_generation_sizes(int collectedGen) {
for (int i = 0; i <= collectedGen; i++) {
_gens[i]->compute_new_size();
}
}
GenCollectedHeap* GenCollectedHeap::heap() {
assert(_gch != NULL, "Uninitialized access to GenCollectedHeap::heap()");
assert(_gch->kind() == CollectedHeap::GenCollectedHeap, "not a generational heap");
return _gch;
}
void GenCollectedHeap::prepare_for_compaction() {
Generation* scanning_gen = _gens[_n_gens-1];
// Start by compacting into same gen.
CompactPoint cp(scanning_gen, NULL, NULL);
while (scanning_gen != NULL) {
scanning_gen->prepare_for_compaction(&cp);
scanning_gen = prev_gen(scanning_gen);
}
}
GCStats* GenCollectedHeap::gc_stats(int level) const {
return _gens[level]->gc_stats();
}
void GenCollectedHeap::verify(bool allow_dirty, bool silent, VerifyOption option /* ignored */) {
if (!silent) {
gclog_or_tty->print("permgen ");
}
perm_gen()->verify(allow_dirty);
for (int i = _n_gens-1; i >= 0; i--) {
Generation* g = _gens[i];
if (!silent) {
gclog_or_tty->print(g->name());
gclog_or_tty->print(" ");
}
g->verify(allow_dirty);
}
if (!silent) {
gclog_or_tty->print("remset ");
}
rem_set()->verify();
}
void GenCollectedHeap::print() const { print_on(tty); }
void GenCollectedHeap::print_on(outputStream* st) const {
for (int i = 0; i < _n_gens; i++) {
_gens[i]->print_on(st);
}
perm_gen()->print_on(st);
}
void GenCollectedHeap::gc_threads_do(ThreadClosure* tc) const {
if (workers() != NULL) {
workers()->threads_do(tc);
}
#ifndef SERIALGC
if (UseConcMarkSweepGC) {
ConcurrentMarkSweepThread::threads_do(tc);
}
#endif // SERIALGC
}
void GenCollectedHeap::print_gc_threads_on(outputStream* st) const {
#ifndef SERIALGC
if (UseParNewGC) {
workers()->print_worker_threads_on(st);
}
if (UseConcMarkSweepGC) {
ConcurrentMarkSweepThread::print_all_on(st);
}
#endif // SERIALGC
}
void GenCollectedHeap::print_tracing_info() const {
if (TraceGen0Time) {
get_gen(0)->print_summary_info();
}
if (TraceGen1Time) {
get_gen(1)->print_summary_info();
}
}
void GenCollectedHeap::print_heap_change(size_t prev_used) const {
if (PrintGCDetails && Verbose) {
gclog_or_tty->print(" " SIZE_FORMAT
"->" SIZE_FORMAT
"(" SIZE_FORMAT ")",
prev_used, used(), capacity());
} else {
gclog_or_tty->print(" " SIZE_FORMAT "K"
"->" SIZE_FORMAT "K"
"(" SIZE_FORMAT "K)",
prev_used / K, used() / K, capacity() / K);
}
}
//New method to print perm gen info with PrintGCDetails flag
void GenCollectedHeap::print_perm_heap_change(size_t perm_prev_used) const {
gclog_or_tty->print(", [%s :", perm_gen()->short_name());
perm_gen()->print_heap_change(perm_prev_used);
gclog_or_tty->print("]");
}
class GenGCPrologueClosure: public GenCollectedHeap::GenClosure {
private:
bool _full;
public:
void do_generation(Generation* gen) {
gen->gc_prologue(_full);
}
GenGCPrologueClosure(bool full) : _full(full) {};
};
void GenCollectedHeap::gc_prologue(bool full) {
assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
always_do_update_barrier = false;
// Fill TLAB's and such
CollectedHeap::accumulate_statistics_all_tlabs();
ensure_parsability(true); // retire TLABs
// Call allocation profiler
AllocationProfiler::iterate_since_last_gc();
// Walk generations
GenGCPrologueClosure blk(full);
generation_iterate(&blk, false); // not old-to-young.
perm_gen()->gc_prologue(full);
};
class GenGCEpilogueClosure: public GenCollectedHeap::GenClosure {
private:
bool _full;
public:
void do_generation(Generation* gen) {
gen->gc_epilogue(_full);
}
GenGCEpilogueClosure(bool full) : _full(full) {};
};
void GenCollectedHeap::gc_epilogue(bool full) {
#ifdef COMPILER2
assert(DerivedPointerTable::is_empty(), "derived pointer present");
size_t actual_gap = pointer_delta((HeapWord*) (max_uintx-3), *(end_addr()));
guarantee(actual_gap > (size_t)FastAllocateSizeLimit, "inline allocation wraps");
#endif /* COMPILER2 */
resize_all_tlabs();
GenGCEpilogueClosure blk(full);
generation_iterate(&blk, false); // not old-to-young.
perm_gen()->gc_epilogue(full);
if (!CleanChunkPoolAsync) {
Chunk::clean_chunk_pool();
}
always_do_update_barrier = UseConcMarkSweepGC;
};
#ifndef PRODUCT
class GenGCSaveTopsBeforeGCClosure: public GenCollectedHeap::GenClosure {
private:
public:
void do_generation(Generation* gen) {
gen->record_spaces_top();
}
};
void GenCollectedHeap::record_gen_tops_before_GC() {
if (ZapUnusedHeapArea) {
GenGCSaveTopsBeforeGCClosure blk;
generation_iterate(&blk, false); // not old-to-young.
perm_gen()->record_spaces_top();
}
}
#endif // not PRODUCT
class GenEnsureParsabilityClosure: public GenCollectedHeap::GenClosure {
public:
void do_generation(Generation* gen) {
gen->ensure_parsability();
}
};
void GenCollectedHeap::ensure_parsability(bool retire_tlabs) {
CollectedHeap::ensure_parsability(retire_tlabs);
GenEnsureParsabilityClosure ep_cl;
generation_iterate(&ep_cl, false);
perm_gen()->ensure_parsability();
}
oop GenCollectedHeap::handle_failed_promotion(Generation* gen,
oop obj,
size_t obj_size) {
assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
HeapWord* result = NULL;
// First give each higher generation a chance to allocate the promoted object.
Generation* allocator = next_gen(gen);
if (allocator != NULL) {
do {
result = allocator->allocate(obj_size, false);
} while (result == NULL && (allocator = next_gen(allocator)) != NULL);
}
if (result == NULL) {
// Then give gen and higher generations a chance to expand and allocate the
// object.
do {
result = gen->expand_and_allocate(obj_size, false);
} while (result == NULL && (gen = next_gen(gen)) != NULL);
}
if (result != NULL) {
Copy::aligned_disjoint_words((HeapWord*)obj, result, obj_size);
}
return oop(result);
}
class GenTimeOfLastGCClosure: public GenCollectedHeap::GenClosure {
jlong _time; // in ms
jlong _now; // in ms
public:
GenTimeOfLastGCClosure(jlong now) : _time(now), _now(now) { }
jlong time() { return _time; }
void do_generation(Generation* gen) {
_time = MIN2(_time, gen->time_of_last_gc(_now));
}
};
jlong GenCollectedHeap::millis_since_last_gc() {
jlong now = os::javaTimeMillis();
GenTimeOfLastGCClosure tolgc_cl(now);
// iterate over generations getting the oldest
// time that a generation was collected
generation_iterate(&tolgc_cl, false);
tolgc_cl.do_generation(perm_gen());
// XXX Despite the assert above, since javaTimeMillis()
// doesnot guarantee monotonically increasing return
// values (note, i didn't say "strictly monotonic"),
// we need to guard against getting back a time
// later than now. This should be fixed by basing
// on someting like gethrtime() which guarantees
// monotonicity. Note that cond_wait() is susceptible
// to a similar problem, because its interface is
// based on absolute time in the form of the
// system time's notion of UCT. See also 4506635
// for yet another problem of similar nature. XXX
jlong retVal = now - tolgc_cl.time();
if (retVal < 0) {
NOT_PRODUCT(warning("time warp: %d", retVal);)
return 0;
}
return retVal;
}