/**
* 标记清除的方式回收内存堆的垃圾对象
* 1.第一步: 标记所有存活的对象
* 2.第二步: 计算存活的对象在其内存区压缩后的偏移位置
* 3.第三步: 遍历所有存活的对象并修改其对应的地址映射表
* 4.第四步: 移动存活的对象压缩内存区
*/
void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp,
bool clear_all_softrefs) {
assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
GenCollectedHeap* gch = GenCollectedHeap::heap();
#ifdef ASSERT
if (gch->collector_policy()->should_clear_all_soft_refs()) {
assert(clear_all_softrefs, "Policy should have been checked earlier");
}
#endif
// hook up weak ref data so it can be used during Mark-Sweep
assert(ref_processor() == NULL, "no stomping");
assert(rp != NULL, "should be non-NULL");
_ref_processor = rp;
rp->setup_policy(clear_all_softrefs);
TraceTime t1("Full GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);
// When collecting the permanent generation methodOops may be moving,
// so we either have to flush all bcp data or convert it into bci.
CodeCache::gc_prologue();
Threads::gc_prologue();
// Increment the invocation count for the permanent generation, since it is
// implicitly collected whenever we do a full mark sweep collection.
gch->perm_gen()->stat_record()->invocations++;
//本次Gc之前内存堆的使用量
size_t gch_prev_used = gch->used();
// Some of the card table updates below assume that the perm gen is
// also being collected.
assert(level == gch->n_gens() - 1, "All generations are being collected, ergo perm gen too.");
// Capture used regions for each generation that will be
// subject to collection, so that card table adjustments can
// be made intelligently (see clear / invalidate further below).
gch->save_used_regions(level, true /* perm */);
allocate_stacks();
mark_sweep_phase1(level, clear_all_softrefs);
mark_sweep_phase2();
// Don't add any more derived pointers during phase3
COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
mark_sweep_phase3(level);
VALIDATE_MARK_SWEEP_ONLY(
if (ValidateMarkSweep) {
guarantee(_root_refs_stack->length() == 0, "should be empty by now");
}
)
void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
bool clear_all_softrefs) {
assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
SharedHeap* sh = SharedHeap::heap();
#ifdef ASSERT
if (sh->collector_policy()->should_clear_all_soft_refs()) {
assert(clear_all_softrefs, "Policy should have been checked earler");
}
#endif
// hook up weak ref data so it can be used during Mark-Sweep
assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
assert(rp != NULL, "should be non-NULL");
assert(rp == G1CollectedHeap::heap()->ref_processor_stw(), "Precondition");
GenMarkSweep::_ref_processor = rp;
rp->setup_policy(clear_all_softrefs);
// When collecting the permanent generation Method*s may be moving,
// so we either have to flush all bcp data or convert it into bci.
CodeCache::gc_prologue();
Threads::gc_prologue();
bool marked_for_unloading = false;
allocate_stacks();
// We should save the marks of the currently locked biased monitors.
// The marking doesn't preserve the marks of biased objects.
BiasedLocking::preserve_marks();
mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
mark_sweep_phase2();
// Don't add any more derived pointers during phase3
COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
mark_sweep_phase3();
mark_sweep_phase4();
GenMarkSweep::restore_marks();
BiasedLocking::restore_marks();
GenMarkSweep::deallocate_stacks();
// "free at last gc" is calculated from these.
// CHF: cheating for now!!!
// Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity());
// Universe::set_heap_used_at_last_gc(Universe::heap()->used());
Threads::gc_epilogue();
CodeCache::gc_epilogue();
JvmtiExport::gc_epilogue();
// refs processing: clean slate
GenMarkSweep::_ref_processor = NULL;
}
// This method contains no policy. You should probably
// be calling invoke() instead.
void PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
assert(ref_processor() != NULL, "Sanity");
if (GC_locker::check_active_before_gc()) {
return;
}
ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
GCCause::Cause gc_cause = heap->gc_cause();
assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
PSAdaptiveSizePolicy* size_policy = heap->size_policy();
PSYoungGen* young_gen = heap->young_gen();
PSOldGen* old_gen = heap->old_gen();
PSPermGen* perm_gen = heap->perm_gen();
// Increment the invocation count
heap->increment_total_collections(true /* full */);
// Save information needed to minimize mangling
heap->record_gen_tops_before_GC();
// We need to track unique mark sweep invocations as well.
_total_invocations++;
AdaptiveSizePolicyOutput(size_policy, heap->total_collections());
if (PrintHeapAtGC) {
Universe::print_heap_before_gc();
}
// Fill in TLABs
heap->accumulate_statistics_all_tlabs();
heap->ensure_parsability(true); // retire TLABs
if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
HandleMark hm; // Discard invalid handles created during verification
gclog_or_tty->print(" VerifyBeforeGC:");
Universe::verify(true);
}
// Verify object start arrays
if (VerifyObjectStartArray &&
VerifyBeforeGC) {
old_gen->verify_object_start_array();
perm_gen->verify_object_start_array();
}
heap->pre_full_gc_dump();
// Filled in below to track the state of the young gen after the collection.
bool eden_empty;
bool survivors_empty;
bool young_gen_empty;
{
HandleMark hm;
const bool is_system_gc = gc_cause == GCCause::_java_lang_system_gc;
// This is useful for debugging but don't change the output the
// the customer sees.
const char* gc_cause_str = "Full GC";
if (is_system_gc && PrintGCDetails) {
gc_cause_str = "Full GC (System)";
}
gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
TraceTime t1(gc_cause_str, PrintGC, !PrintGCDetails, gclog_or_tty);
TraceCollectorStats tcs(counters());
TraceMemoryManagerStats tms(true /* Full GC */);
if (TraceGen1Time) accumulated_time()->start();
// Let the size policy know we're starting
size_policy->major_collection_begin();
// When collecting the permanent generation methodOops may be moving,
// so we either have to flush all bcp data or convert it into bci.
CodeCache::gc_prologue();
Threads::gc_prologue();
BiasedLocking::preserve_marks();
// Capture heap size before collection for printing.
size_t prev_used = heap->used();
// Capture perm gen size before collection for sizing.
size_t perm_gen_prev_used = perm_gen->used_in_bytes();
// For PrintGCDetails
size_t old_gen_prev_used = old_gen->used_in_bytes();
size_t young_gen_prev_used = young_gen->used_in_bytes();
allocate_stacks();
NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
COMPILER2_PRESENT(DerivedPointerTable::clear());
ref_processor()->enable_discovery();
ref_processor()->setup_policy(clear_all_softrefs);
mark_sweep_phase1(clear_all_softrefs);
mark_sweep_phase2();
// Don't add any more derived pointers during phase3
COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
mark_sweep_phase3();
mark_sweep_phase4();
restore_marks();
deallocate_stacks();
if (ZapUnusedHeapArea) {
// Do a complete mangle (top to end) because the usage for
// scratch does not maintain a top pointer.
young_gen->to_space()->mangle_unused_area_complete();
}
eden_empty = young_gen->eden_space()->is_empty();
if (!eden_empty) {
eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
}
// Update heap occupancy information which is used as
// input to soft ref clearing policy at the next gc.
Universe::update_heap_info_at_gc();
survivors_empty = young_gen->from_space()->is_empty() &&
young_gen->to_space()->is_empty();
young_gen_empty = eden_empty && survivors_empty;
BarrierSet* bs = heap->barrier_set();
if (bs->is_a(BarrierSet::ModRef)) {
ModRefBarrierSet* modBS = (ModRefBarrierSet*)bs;
MemRegion old_mr = heap->old_gen()->reserved();
MemRegion perm_mr = heap->perm_gen()->reserved();
assert(perm_mr.end() <= old_mr.start(), "Generations out of order");
if (young_gen_empty) {
modBS->clear(MemRegion(perm_mr.start(), old_mr.end()));
} else {
modBS->invalidate(MemRegion(perm_mr.start(), old_mr.end()));
}
}
BiasedLocking::restore_marks();
Threads::gc_epilogue();
CodeCache::gc_epilogue();
COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
ref_processor()->enqueue_discovered_references(NULL);
// Update time of last GC
reset_millis_since_last_gc();
// Let the size policy know we're done
size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
if (UseAdaptiveSizePolicy) {
if (PrintAdaptiveSizePolicy) {
gclog_or_tty->print("AdaptiveSizeStart: ");
gclog_or_tty->stamp();
gclog_or_tty->print_cr(" collection: %d ",
heap->total_collections());
if (Verbose) {
gclog_or_tty->print("old_gen_capacity: %d young_gen_capacity: %d"
" perm_gen_capacity: %d ",
old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes(),
perm_gen->capacity_in_bytes());
}
}
// Don't check if the size_policy is ready here. Let
// the size_policy check that internally.
if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
((gc_cause != GCCause::_java_lang_system_gc) ||
UseAdaptiveSizePolicyWithSystemGC)) {
// Calculate optimal free space amounts
assert(young_gen->max_size() >
young_gen->from_space()->capacity_in_bytes() +
young_gen->to_space()->capacity_in_bytes(),
"Sizes of space in young gen are out-of-bounds");
size_t max_eden_size = young_gen->max_size() -
young_gen->from_space()->capacity_in_bytes() -
young_gen->to_space()->capacity_in_bytes();
size_policy->compute_generation_free_space(young_gen->used_in_bytes(),
young_gen->eden_space()->used_in_bytes(),
old_gen->used_in_bytes(),
perm_gen->used_in_bytes(),
young_gen->eden_space()->capacity_in_bytes(),
old_gen->max_gen_size(),
max_eden_size,
true /* full gc*/,
gc_cause);
heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
// Don't resize the young generation at an major collection. A
// desired young generation size may have been calculated but
// resizing the young generation complicates the code because the
// resizing of the old generation may have moved the boundary
// between the young generation and the old generation. Let the
// young generation resizing happen at the minor collections.
}
if (PrintAdaptiveSizePolicy) {
gclog_or_tty->print_cr("AdaptiveSizeStop: collection: %d ",
heap->total_collections());
}
}
if (UsePerfData) {
heap->gc_policy_counters()->update_counters();
heap->gc_policy_counters()->update_old_capacity(
old_gen->capacity_in_bytes());
heap->gc_policy_counters()->update_young_capacity(
young_gen->capacity_in_bytes());
}
heap->resize_all_tlabs();
// We collected the perm gen, so we'll resize it here.
perm_gen->compute_new_size(perm_gen_prev_used);
if (TraceGen1Time) accumulated_time()->stop();
if (PrintGC) {
if (PrintGCDetails) {
// Don't print a GC timestamp here. This is after the GC so
// would be confusing.
young_gen->print_used_change(young_gen_prev_used);
old_gen->print_used_change(old_gen_prev_used);
}
heap->print_heap_change(prev_used);
// Do perm gen after heap becase prev_used does
// not include the perm gen (done this way in the other
// collectors).
if (PrintGCDetails) {
perm_gen->print_used_change(perm_gen_prev_used);
}
}
// Track memory usage and detect low memory
MemoryService::track_memory_usage();
heap->update_counters();
if (PrintGCDetails) {
if (size_policy->print_gc_time_limit_would_be_exceeded()) {
if (size_policy->gc_time_limit_exceeded()) {
gclog_or_tty->print_cr(" GC time is exceeding GCTimeLimit "
"of %d%%", GCTimeLimit);
} else {
gclog_or_tty->print_cr(" GC time would exceed GCTimeLimit "
"of %d%%", GCTimeLimit);
}
}
size_policy->set_print_gc_time_limit_would_be_exceeded(false);
}
}
if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
HandleMark hm; // Discard invalid handles created during verification
gclog_or_tty->print(" VerifyAfterGC:");
Universe::verify(false);
}
// Re-verify object start arrays
if (VerifyObjectStartArray &&
VerifyAfterGC) {
old_gen->verify_object_start_array();
perm_gen->verify_object_start_array();
}
if (ZapUnusedHeapArea) {
old_gen->object_space()->check_mangled_unused_area_complete();
perm_gen->object_space()->check_mangled_unused_area_complete();
}
NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
if (PrintHeapAtGC) {
Universe::print_heap_after_gc();
}
heap->post_full_gc_dump();
#ifdef TRACESPINNING
ParallelTaskTerminator::print_termination_counts();
#endif
}
// This method contains no policy. You should probably
// be calling invoke() instead.
bool PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
assert(ref_processor() != NULL, "Sanity");
if (GC_locker::check_active_before_gc()) {
return false;
}
ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
GCCause::Cause gc_cause = heap->gc_cause();
_gc_timer->register_gc_start();
_gc_tracer->report_gc_start(gc_cause, _gc_timer->gc_start());
PSAdaptiveSizePolicy* size_policy = heap->size_policy();
// The scope of casr should end after code that can change
// CollectorPolicy::_should_clear_all_soft_refs.
ClearedAllSoftRefs casr(clear_all_softrefs, heap->collector_policy());
PSYoungGen* young_gen = heap->young_gen();
PSOldGen* old_gen = heap->old_gen();
// Increment the invocation count
heap->increment_total_collections(true /* full */);
// Save information needed to minimize mangling
heap->record_gen_tops_before_GC();
// We need to track unique mark sweep invocations as well.
_total_invocations++;
AdaptiveSizePolicyOutput(size_policy, heap->total_collections());
heap->print_heap_before_gc();
heap->trace_heap_before_gc(_gc_tracer);
// Fill in TLABs
heap->accumulate_statistics_all_tlabs();
heap->ensure_parsability(true); // retire TLABs
if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
HandleMark hm; // Discard invalid handles created during verification
Universe::verify(" VerifyBeforeGC:");
}
// Verify object start arrays
if (VerifyObjectStartArray &&
VerifyBeforeGC) {
old_gen->verify_object_start_array();
}
heap->pre_full_gc_dump(_gc_timer);
// Filled in below to track the state of the young gen after the collection.
bool eden_empty;
bool survivors_empty;
bool young_gen_empty;
{
HandleMark hm;
TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
GCTraceTime t1(GCCauseString("Full GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer->gc_id());
TraceCollectorStats tcs(counters());
TraceMemoryManagerStats tms(true /* Full GC */,gc_cause);
if (TraceOldGenTime) accumulated_time()->start();
// Let the size policy know we're starting
size_policy->major_collection_begin();
CodeCache::gc_prologue();
BiasedLocking::preserve_marks();
// Capture heap size before collection for printing.
size_t prev_used = heap->used();
// Capture metadata size before collection for sizing.
size_t metadata_prev_used = MetaspaceAux::used_bytes();
// For PrintGCDetails
size_t old_gen_prev_used = old_gen->used_in_bytes();
size_t young_gen_prev_used = young_gen->used_in_bytes();
allocate_stacks();
COMPILER2_PRESENT(DerivedPointerTable::clear());
ref_processor()->enable_discovery();
ref_processor()->setup_policy(clear_all_softrefs);
mark_sweep_phase1(clear_all_softrefs);
mark_sweep_phase2();
// Don't add any more derived pointers during phase3
COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
mark_sweep_phase3();
mark_sweep_phase4();
restore_marks();
deallocate_stacks();
if (ZapUnusedHeapArea) {
// Do a complete mangle (top to end) because the usage for
// scratch does not maintain a top pointer.
young_gen->to_space()->mangle_unused_area_complete();
}
eden_empty = young_gen->eden_space()->is_empty();
if (!eden_empty) {
eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
}
// Update heap occupancy information which is used as
// input to soft ref clearing policy at the next gc.
Universe::update_heap_info_at_gc();
survivors_empty = young_gen->from_space()->is_empty() &&
young_gen->to_space()->is_empty();
young_gen_empty = eden_empty && survivors_empty;
ModRefBarrierSet* modBS = barrier_set_cast<ModRefBarrierSet>(heap->barrier_set());
MemRegion old_mr = heap->old_gen()->reserved();
if (young_gen_empty) {
modBS->clear(MemRegion(old_mr.start(), old_mr.end()));
} else {
modBS->invalidate(MemRegion(old_mr.start(), old_mr.end()));
}
// Delete metaspaces for unloaded class loaders and clean up loader_data graph
ClassLoaderDataGraph::purge();
MetaspaceAux::verify_metrics();
BiasedLocking::restore_marks();
CodeCache::gc_epilogue();
JvmtiExport::gc_epilogue();
COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
ref_processor()->enqueue_discovered_references(NULL);
// Update time of last GC
reset_millis_since_last_gc();
// Let the size policy know we're done
size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);
if (UseAdaptiveSizePolicy) {
if (PrintAdaptiveSizePolicy) {
gclog_or_tty->print("AdaptiveSizeStart: ");
gclog_or_tty->stamp();
gclog_or_tty->print_cr(" collection: %d ",
heap->total_collections());
if (Verbose) {
gclog_or_tty->print("old_gen_capacity: " SIZE_FORMAT
" young_gen_capacity: " SIZE_FORMAT,
old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
}
}
// Don't check if the size_policy is ready here. Let
// the size_policy check that internally.
if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&
((gc_cause != GCCause::_java_lang_system_gc) ||
UseAdaptiveSizePolicyWithSystemGC)) {
// Swap the survivor spaces if from_space is empty. The
// resize_young_gen() called below is normally used after
// a successful young GC and swapping of survivor spaces;
// otherwise, it will fail to resize the young gen with
// the current implementation.
if (young_gen->from_space()->is_empty()) {
young_gen->from_space()->clear(SpaceDecorator::Mangle);
young_gen->swap_spaces();
}
// Calculate optimal free space amounts
assert(young_gen->max_size() >
young_gen->from_space()->capacity_in_bytes() +
young_gen->to_space()->capacity_in_bytes(),
"Sizes of space in young gen are out-of-bounds");
size_t young_live = young_gen->used_in_bytes();
size_t eden_live = young_gen->eden_space()->used_in_bytes();
size_t old_live = old_gen->used_in_bytes();
size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
size_t max_old_gen_size = old_gen->max_gen_size();
size_t max_eden_size = young_gen->max_size() -
young_gen->from_space()->capacity_in_bytes() -
young_gen->to_space()->capacity_in_bytes();
// Used for diagnostics
size_policy->clear_generation_free_space_flags();
size_policy->compute_generations_free_space(young_live,
eden_live,
old_live,
cur_eden,
max_old_gen_size,
max_eden_size,
true /* full gc*/);
size_policy->check_gc_overhead_limit(young_live,
eden_live,
max_old_gen_size,
max_eden_size,
true /* full gc*/,
gc_cause,
heap->collector_policy());
size_policy->decay_supplemental_growth(true /* full gc*/);
heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
size_policy->calculated_survivor_size_in_bytes());
}
if (PrintAdaptiveSizePolicy) {
gclog_or_tty->print_cr("AdaptiveSizeStop: collection: %d ",
heap->total_collections());
}
}
if (UsePerfData) {
heap->gc_policy_counters()->update_counters();
heap->gc_policy_counters()->update_old_capacity(
old_gen->capacity_in_bytes());
heap->gc_policy_counters()->update_young_capacity(
young_gen->capacity_in_bytes());
}
heap->resize_all_tlabs();
// We collected the heap, recalculate the metaspace capacity
MetaspaceGC::compute_new_size();
if (TraceOldGenTime) accumulated_time()->stop();
if (PrintGC) {
if (PrintGCDetails) {
// Don't print a GC timestamp here. This is after the GC so
// would be confusing.
young_gen->print_used_change(young_gen_prev_used);
old_gen->print_used_change(old_gen_prev_used);
}
heap->print_heap_change(prev_used);
if (PrintGCDetails) {
MetaspaceAux::print_metaspace_change(metadata_prev_used);
}
}
// Track memory usage and detect low memory
MemoryService::track_memory_usage();
heap->update_counters();
}
if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
HandleMark hm; // Discard invalid handles created during verification
Universe::verify(" VerifyAfterGC:");
}
// Re-verify object start arrays
if (VerifyObjectStartArray &&
VerifyAfterGC) {
old_gen->verify_object_start_array();
}
if (ZapUnusedHeapArea) {
old_gen->object_space()->check_mangled_unused_area_complete();
}
NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
heap->print_heap_after_gc();
heap->trace_heap_after_gc(_gc_tracer);
heap->post_full_gc_dump(_gc_timer);
#ifdef TRACESPINNING
ParallelTaskTerminator::print_termination_counts();
#endif
_gc_timer->register_gc_end();
_gc_tracer->report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
return true;
}
void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp, bool clear_all_softrefs) {
guarantee(level == 1, "We always collect both old and young.");
assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
GenCollectedHeap* gch = GenCollectedHeap::heap();
#ifdef ASSERT
if (gch->collector_policy()->should_clear_all_soft_refs()) {
assert(clear_all_softrefs, "Policy should have been checked earlier");
}
#endif
// hook up weak ref data so it can be used during Mark-Sweep
assert(ref_processor() == NULL, "no stomping");
assert(rp != NULL, "should be non-NULL");
_ref_processor = rp;
rp->setup_policy(clear_all_softrefs);
GCTraceTime t1(GCCauseString("Full GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer->gc_id());
gch->trace_heap_before_gc(_gc_tracer);
// When collecting the permanent generation Method*s may be moving,
// so we either have to flush all bcp data or convert it into bci.
CodeCache::gc_prologue();
Threads::gc_prologue();
// Increment the invocation count
_total_invocations++;
// Capture heap size before collection for printing.
size_t gch_prev_used = gch->used();
// Capture used regions for each generation that will be
// subject to collection, so that card table adjustments can
// be made intelligently (see clear / invalidate further below).
gch->save_used_regions(level);
allocate_stacks();
mark_sweep_phase1(level, clear_all_softrefs);
mark_sweep_phase2();
// Don't add any more derived pointers during phase3
COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
mark_sweep_phase3(level);
mark_sweep_phase4();
restore_marks();
// Set saved marks for allocation profiler (and other things? -- dld)
// (Should this be in general part?)
gch->save_marks();
deallocate_stacks();
// If compaction completely evacuated all generations younger than this
// one, then we can clear the card table. Otherwise, we must invalidate
// it (consider all cards dirty). In the future, we might consider doing
// compaction within generations only, and doing card-table sliding.
bool all_empty = true;
for (int i = 0; all_empty && i < level; i++) {
Generation* g = gch->get_gen(i);
all_empty = all_empty && gch->get_gen(i)->used() == 0;
}
GenRemSet* rs = gch->rem_set();
Generation* old_gen = gch->get_gen(level);
// Clear/invalidate below make use of the "prev_used_regions" saved earlier.
if (all_empty) {
// We've evacuated all generations below us.
rs->clear_into_younger(old_gen);
} else {
// Invalidate the cards corresponding to the currently used
// region and clear those corresponding to the evacuated region.
rs->invalidate_or_clear(old_gen);
}
Threads::gc_epilogue();
CodeCache::gc_epilogue();
JvmtiExport::gc_epilogue();
if (PrintGC && !PrintGCDetails) {
gch->print_heap_change(gch_prev_used);
}
// refs processing: clean slate
_ref_processor = NULL;
// Update heap occupancy information which is used as
// input to soft ref clearing policy at the next gc.
Universe::update_heap_info_at_gc();
// Update time of last gc for all generations we collected
// (which curently is all the generations in the heap).
// We need to use a monotonically non-deccreasing time in ms
// or we will see time-warp warnings and os::javaTimeMillis()
// does not guarantee monotonicity.
jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
gch->update_time_of_last_gc(now);
gch->trace_heap_after_gc(_gc_tracer);
}
void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
bool clear_all_softrefs) {
// Recursively traverse all live objects and mark them
GCTraceTime tm("phase 1", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
G1CollectedHeap* g1h = G1CollectedHeap::heap();
// Need cleared claim bits for the roots processing
ClassLoaderDataGraph::clear_claimed_marks();
MarkingCodeBlobClosure follow_code_closure(&GenMarkSweep::follow_root_closure, !CodeBlobToOopClosure::FixRelocations);
{
G1RootProcessor root_processor(g1h, 1);
root_processor.process_strong_roots(&GenMarkSweep::follow_root_closure,
&GenMarkSweep::follow_cld_closure,
&follow_code_closure);
}
// Process reference objects found during marking
ReferenceProcessor* rp = GenMarkSweep::ref_processor();
assert(rp == g1h->ref_processor_stw(), "Sanity");
rp->setup_policy(clear_all_softrefs);
const ReferenceProcessorStats& stats =
rp->process_discovered_references(&GenMarkSweep::is_alive,
&GenMarkSweep::keep_alive,
&GenMarkSweep::follow_stack_closure,
NULL,
gc_timer(),
gc_tracer()->gc_id());
gc_tracer()->report_gc_reference_stats(stats);
// This is the point where the entire marking should have completed.
assert(GenMarkSweep::_marking_stack.is_empty(), "Marking should have completed");
// Unload classes and purge the SystemDictionary.
bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
// Unload nmethods.
CodeCache::do_unloading(&GenMarkSweep::is_alive, purged_class);
// Prune dead klasses from subklass/sibling/implementor lists.
Klass::clean_weak_klass_links(&GenMarkSweep::is_alive);
// Delete entries for dead interned string and clean up unreferenced symbols in symbol table.
g1h->unlink_string_and_symbol_table(&GenMarkSweep::is_alive);
if (VerifyDuringGC) {
HandleMark hm; // handle scope
COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
g1h->prepare_for_verify();
// Note: we can verify only the heap here. When an object is
// marked, the previous value of the mark word (including
// identity hash values, ages, etc) is preserved, and the mark
// word is set to markOop::marked_value - effectively removing
// any hash values from the mark word. These hash values are
// used when verifying the dictionaries and so removing them
// from the mark word can make verification of the dictionaries
// fail. At the end of the GC, the original mark word values
// (including hash values) are restored to the appropriate
// objects.
if (!VerifySilently) {
gclog_or_tty->print(" VerifyDuringGC:(full)[Verifying ");
}
g1h->verify(VerifySilently, VerifyOption_G1UseMarkWord);
if (!VerifySilently) {
gclog_or_tty->print_cr("]");
}
}
gc_tracer()->report_object_count_after_gc(&GenMarkSweep::is_alive);
}
void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
bool clear_all_softrefs) {
assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
SharedHeap* sh = SharedHeap::heap();
#ifdef ASSERT
if (sh->collector_policy()->should_clear_all_soft_refs()) {
assert(clear_all_softrefs, "Policy should have been checked earler");
}
#endif
// hook up weak ref data so it can be used during Mark-Sweep
assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
assert(rp != NULL, "should be non-NULL");
GenMarkSweep::_ref_processor = rp;
rp->setup_policy(clear_all_softrefs);
// When collecting the permanent generation methodOops may be moving,
// so we either have to flush all bcp data or convert it into bci.
CodeCache::gc_prologue();
Threads::gc_prologue();
// Increment the invocation count for the permanent generation, since it is
// implicitly collected whenever we do a full mark sweep collection.
sh->perm_gen()->stat_record()->invocations++;
bool marked_for_unloading = false;
allocate_stacks();
// We should save the marks of the currently locked biased monitors.
// The marking doesn't preserve the marks of biased objects.
BiasedLocking::preserve_marks();
mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
if (VerifyDuringGC) {
G1CollectedHeap* g1h = G1CollectedHeap::heap();
g1h->checkConcurrentMark();
}
mark_sweep_phase2();
// Don't add any more derived pointers during phase3
COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
mark_sweep_phase3();
mark_sweep_phase4();
GenMarkSweep::restore_marks();
BiasedLocking::restore_marks();
GenMarkSweep::deallocate_stacks();
// We must invalidate the perm-gen rs, so that it gets rebuilt.
GenRemSet* rs = sh->rem_set();
rs->invalidate(sh->perm_gen()->used_region(), true /*whole_heap*/);
// "free at last gc" is calculated from these.
// CHF: cheating for now!!!
// Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity());
// Universe::set_heap_used_at_last_gc(Universe::heap()->used());
Threads::gc_epilogue();
CodeCache::gc_epilogue();
// refs processing: clean slate
GenMarkSweep::_ref_processor = NULL;
}
// This method contains no policy. You should probably
// be calling invoke() instead.
bool PSScavenge::invoke_no_policy() {
assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
assert(_preserved_mark_stack.is_empty(), "should be empty");
assert(_preserved_oop_stack.is_empty(), "should be empty");
_gc_timer.register_gc_start();
TimeStamp scavenge_entry;
TimeStamp scavenge_midpoint;
TimeStamp scavenge_exit;
scavenge_entry.update();
if (GC_locker::check_active_before_gc()) {
return false;
}
ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
GCCause::Cause gc_cause = heap->gc_cause();
assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
// Check for potential problems.
if (!should_attempt_scavenge()) {
return false;
}
_gc_tracer.report_gc_start(heap->gc_cause(), _gc_timer.gc_start());
bool promotion_failure_occurred = false;
PSYoungGen* young_gen = heap->young_gen();
PSOldGen* old_gen = heap->old_gen();
PSAdaptiveSizePolicy* size_policy = heap->size_policy();
heap->increment_total_collections();
AdaptiveSizePolicyOutput(size_policy, heap->total_collections());
if ((gc_cause != GCCause::_java_lang_system_gc) ||
UseAdaptiveSizePolicyWithSystemGC) {
// Gather the feedback data for eden occupancy.
young_gen->eden_space()->accumulate_statistics();
}
if (ZapUnusedHeapArea) {
// Save information needed to minimize mangling
heap->record_gen_tops_before_GC();
}
heap->print_heap_before_gc();
heap->trace_heap_before_gc(&_gc_tracer);
assert(!NeverTenure || _tenuring_threshold == markOopDesc::max_age + 1, "Sanity");
assert(!AlwaysTenure || _tenuring_threshold == 0, "Sanity");
size_t prev_used = heap->used();
// Fill in TLABs
heap->accumulate_statistics_all_tlabs();
heap->ensure_parsability(true); // retire TLABs
if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
HandleMark hm; // Discard invalid handles created during verification
Universe::verify(" VerifyBeforeGC:");
}
{
ResourceMark rm;
HandleMark hm;
gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
GCTraceTime t1(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
TraceCollectorStats tcs(counters());
TraceMemoryManagerStats tms(false /* not full GC */,gc_cause);
if (TraceGen0Time) accumulated_time()->start();
// Let the size policy know we're starting
size_policy->minor_collection_begin();
// Verify the object start arrays.
if (VerifyObjectStartArray &&
VerifyBeforeGC) {
old_gen->verify_object_start_array();
}
// Verify no unmarked old->young roots
if (VerifyRememberedSets) {
CardTableExtension::verify_all_young_refs_imprecise();
}
if (!ScavengeWithObjectsInToSpace) {
assert(young_gen->to_space()->is_empty(),
"Attempt to scavenge with live objects in to_space");
young_gen->to_space()->clear(SpaceDecorator::Mangle);
} else if (ZapUnusedHeapArea) {
young_gen->to_space()->mangle_unused_area();
}
save_to_space_top_before_gc();
COMPILER2_PRESENT(DerivedPointerTable::clear());
reference_processor()->enable_discovery(true /*verify_disabled*/, true /*verify_no_refs*/);
reference_processor()->setup_policy(false);
// We track how much was promoted to the next generation for
// the AdaptiveSizePolicy.
size_t old_gen_used_before = old_gen->used_in_bytes();
// For PrintGCDetails
size_t young_gen_used_before = young_gen->used_in_bytes();
// Reset our survivor overflow.
set_survivor_overflow(false);
// We need to save the old top values before
// creating the promotion_manager. We pass the top
// values to the card_table, to prevent it from
// straying into the promotion labs.
HeapWord* old_top = old_gen->object_space()->top();
// Release all previously held resources
gc_task_manager()->release_all_resources();
// Set the number of GC threads to be used in this collection
gc_task_manager()->set_active_gang();
gc_task_manager()->task_idle_workers();
// Get the active number of workers here and use that value
// throughout the methods.
uint active_workers = gc_task_manager()->active_workers();
heap->set_par_threads(active_workers);
PSPromotionManager::pre_scavenge();
// We'll use the promotion manager again later.
PSPromotionManager* promotion_manager = PSPromotionManager::vm_thread_promotion_manager();
{
GCTraceTime tm("Scavenge", false, false, &_gc_timer);
ParallelScavengeHeap::ParStrongRootsScope psrs;
GCTaskQueue* q = GCTaskQueue::create();
if (!old_gen->object_space()->is_empty()) {
// There are only old-to-young pointers if there are objects
// in the old gen.
uint stripe_total = active_workers;
for(uint i=0; i < stripe_total; i++) {
q->enqueue(new OldToYoungRootsTask(old_gen, old_top, i, stripe_total));
}
}
q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::universe));
q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::jni_handles));
// We scan the thread roots in parallel
Threads::create_thread_roots_tasks(q);
q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::object_synchronizer));
q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::flat_profiler));
q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::management));
q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::system_dictionary));
q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::class_loader_data));
q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::jvmti));
q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::code_cache));
ParallelTaskTerminator terminator(
active_workers,
(TaskQueueSetSuper*) promotion_manager->stack_array_depth());
if (active_workers > 1) {
for (uint j = 0; j < active_workers; j++) {
q->enqueue(new StealTask(&terminator));
}
}
gc_task_manager()->execute_and_wait(q);
}
scavenge_midpoint.update();
// Process reference objects discovered during scavenge
{
GCTraceTime tm("References", false, false, &_gc_timer);
reference_processor()->setup_policy(false); // not always_clear
reference_processor()->set_active_mt_degree(active_workers);
PSKeepAliveClosure keep_alive(promotion_manager);
PSEvacuateFollowersClosure evac_followers(promotion_manager);
ReferenceProcessorStats stats;
if (reference_processor()->processing_is_mt()) {
PSRefProcTaskExecutor task_executor;
stats = reference_processor()->process_discovered_references(
&_is_alive_closure, &keep_alive, &evac_followers, &task_executor,
&_gc_timer);
} else {
stats = reference_processor()->process_discovered_references(
&_is_alive_closure, &keep_alive, &evac_followers, NULL, &_gc_timer);
}
_gc_tracer.report_gc_reference_stats(stats);
// Enqueue reference objects discovered during scavenge.
if (reference_processor()->processing_is_mt()) {
PSRefProcTaskExecutor task_executor;
reference_processor()->enqueue_discovered_references(&task_executor);
} else {
reference_processor()->enqueue_discovered_references(NULL);
}
}
{
GCTraceTime tm("StringTable", false, false, &_gc_timer);
// Unlink any dead interned Strings and process the remaining live ones.
PSScavengeRootsClosure root_closure(promotion_manager);
StringTable::unlink_or_oops_do(&_is_alive_closure, &root_closure);
}
// Finally, flush the promotion_manager's labs, and deallocate its stacks.
promotion_failure_occurred = PSPromotionManager::post_scavenge(_gc_tracer);
if (promotion_failure_occurred) {
clean_up_failed_promotion();
if (PrintGC) {
gclog_or_tty->print("--");
}
}
// Let the size policy know we're done. Note that we count promotion
// failure cleanup time as part of the collection (otherwise, we're
// implicitly saying it's mutator time).
size_policy->minor_collection_end(gc_cause);
if (!promotion_failure_occurred) {
// Swap the survivor spaces.
young_gen->eden_space()->clear(SpaceDecorator::Mangle);
young_gen->from_space()->clear(SpaceDecorator::Mangle);
young_gen->swap_spaces();
size_t survived = young_gen->from_space()->used_in_bytes();
size_t promoted = old_gen->used_in_bytes() - old_gen_used_before;
size_policy->update_averages(_survivor_overflow, survived, promoted);
// A successful scavenge should restart the GC time limit count which is
// for full GC's.
size_policy->reset_gc_overhead_limit_count();
if (UseAdaptiveSizePolicy) {
// Calculate the new survivor size and tenuring threshold
if (PrintAdaptiveSizePolicy) {
gclog_or_tty->print("AdaptiveSizeStart: ");
gclog_or_tty->stamp();
gclog_or_tty->print_cr(" collection: %d ",
heap->total_collections());
if (Verbose) {
gclog_or_tty->print("old_gen_capacity: %d young_gen_capacity: %d",
old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
}
}
if (UsePerfData) {
PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
counters->update_old_eden_size(
size_policy->calculated_eden_size_in_bytes());
counters->update_old_promo_size(
size_policy->calculated_promo_size_in_bytes());
counters->update_old_capacity(old_gen->capacity_in_bytes());
counters->update_young_capacity(young_gen->capacity_in_bytes());
counters->update_survived(survived);
counters->update_promoted(promoted);
counters->update_survivor_overflowed(_survivor_overflow);
}
size_t max_young_size = young_gen->max_size();
// Deciding a free ratio in the young generation is tricky, so if
// MinHeapFreeRatio or MaxHeapFreeRatio are in use (implicating
// that the old generation size may have been limited because of them) we
// should then limit our young generation size using NewRatio to have it
// follow the old generation size.
if (MinHeapFreeRatio != 0 || MaxHeapFreeRatio != 100) {
max_young_size = MIN2(old_gen->capacity_in_bytes() / NewRatio, young_gen->max_size());
}
size_t survivor_limit =
size_policy->max_survivor_size(max_young_size);
_tenuring_threshold =
size_policy->compute_survivor_space_size_and_threshold(
_survivor_overflow,
_tenuring_threshold,
survivor_limit);
if (PrintTenuringDistribution) {
gclog_or_tty->cr();
gclog_or_tty->print_cr("Desired survivor size " SIZE_FORMAT " bytes, new threshold %u (max %u)",
size_policy->calculated_survivor_size_in_bytes(),
_tenuring_threshold, MaxTenuringThreshold);
}
if (UsePerfData) {
PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
counters->update_tenuring_threshold(_tenuring_threshold);
counters->update_survivor_size_counters();
}
// Do call at minor collections?
// Don't check if the size_policy is ready at this
// level. Let the size_policy check that internally.
if (UseAdaptiveGenerationSizePolicyAtMinorCollection &&
((gc_cause != GCCause::_java_lang_system_gc) ||
UseAdaptiveSizePolicyWithSystemGC)) {
// Calculate optimial free space amounts
assert(young_gen->max_size() >
young_gen->from_space()->capacity_in_bytes() +
young_gen->to_space()->capacity_in_bytes(),
"Sizes of space in young gen are out-of-bounds");
size_t young_live = young_gen->used_in_bytes();
size_t eden_live = young_gen->eden_space()->used_in_bytes();
size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
size_t max_old_gen_size = old_gen->max_gen_size();
size_t max_eden_size = max_young_size -
young_gen->from_space()->capacity_in_bytes() -
young_gen->to_space()->capacity_in_bytes();
// Used for diagnostics
size_policy->clear_generation_free_space_flags();
size_policy->compute_eden_space_size(young_live,
eden_live,
cur_eden,
max_eden_size,
false /* not full gc*/);
size_policy->check_gc_overhead_limit(young_live,
eden_live,
max_old_gen_size,
max_eden_size,
false /* not full gc*/,
gc_cause,
heap->collector_policy());
size_policy->decay_supplemental_growth(false /* not full gc*/);
}
// Resize the young generation at every collection
// even if new sizes have not been calculated. This is
// to allow resizes that may have been inhibited by the
// relative location of the "to" and "from" spaces.
// Resizing the old gen at minor collects can cause increases
// that don't feed back to the generation sizing policy until
// a major collection. Don't resize the old gen here.
heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
size_policy->calculated_survivor_size_in_bytes());
if (PrintAdaptiveSizePolicy) {
gclog_or_tty->print_cr("AdaptiveSizeStop: collection: %d ",
heap->total_collections());
}
}
// Update the structure of the eden. With NUMA-eden CPU hotplugging or offlining can
// cause the change of the heap layout. Make sure eden is reshaped if that's the case.
// Also update() will case adaptive NUMA chunk resizing.
assert(young_gen->eden_space()->is_empty(), "eden space should be empty now");
young_gen->eden_space()->update();
heap->gc_policy_counters()->update_counters();
heap->resize_all_tlabs();
assert(young_gen->to_space()->is_empty(), "to space should be empty now");
}
COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
NOT_PRODUCT(reference_processor()->verify_no_references_recorded());
{
GCTraceTime tm("Prune Scavenge Root Methods", false, false, &_gc_timer);
CodeCache::prune_scavenge_root_nmethods();
}
// Re-verify object start arrays
if (VerifyObjectStartArray &&
VerifyAfterGC) {
old_gen->verify_object_start_array();
}
// Verify all old -> young cards are now precise
if (VerifyRememberedSets) {
// Precise verification will give false positives. Until this is fixed,
// use imprecise verification.
// CardTableExtension::verify_all_young_refs_precise();
CardTableExtension::verify_all_young_refs_imprecise();
}
if (TraceGen0Time) accumulated_time()->stop();
if (PrintGC) {
if (PrintGCDetails) {
// Don't print a GC timestamp here. This is after the GC so
// would be confusing.
young_gen->print_used_change(young_gen_used_before);
}
heap->print_heap_change(prev_used);
}
// Track memory usage and detect low memory
MemoryService::track_memory_usage();
heap->update_counters();
gc_task_manager()->release_idle_workers();
}
if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
HandleMark hm; // Discard invalid handles created during verification
Universe::verify(" VerifyAfterGC:");
}
heap->print_heap_after_gc();
heap->trace_heap_after_gc(&_gc_tracer);
_gc_tracer.report_tenuring_threshold(tenuring_threshold());
if (ZapUnusedHeapArea) {
young_gen->eden_space()->check_mangled_unused_area_complete();
young_gen->from_space()->check_mangled_unused_area_complete();
young_gen->to_space()->check_mangled_unused_area_complete();
}
scavenge_exit.update();
if (PrintGCTaskTimeStamps) {
tty->print_cr("VM-Thread " INT64_FORMAT " " INT64_FORMAT " " INT64_FORMAT,
scavenge_entry.ticks(), scavenge_midpoint.ticks(),
scavenge_exit.ticks());
gc_task_manager()->print_task_time_stamps();
}
#ifdef TRACESPINNING
ParallelTaskTerminator::print_termination_counts();
#endif
_gc_timer.register_gc_end();
_gc_tracer.report_gc_end(_gc_timer.gc_end(), _gc_timer.time_partitions());
return !promotion_failure_occurred;
}
