/**
* 当前是否需要尝试在旧生代分配内存
* 1).待分配的内存大小 > 年青代容量
* 2).当前内存堆需要一次GC
* 3).内存堆的增量式GC刚刚失败
*/
bool GenCollectorPolicy::should_try_older_generation_allocation(
size_t word_size) const {
GenCollectedHeap* gch = GenCollectedHeap::heap();
size_t gen0_capacity = gch->get_gen(0)->capacity_before_gc();
return (word_size > heap_word_size(gen0_capacity))
|| GC_locker::is_active_and_needs_gc() || gch->incremental_collection_failed();
}
void DefNewGeneration::collect(bool full,
bool clear_all_soft_refs,
size_t size,
bool is_tlab) {
assert(full || size > 0, "otherwise we don't want to collect");
GenCollectedHeap* gch = GenCollectedHeap::heap();
_gc_timer->register_gc_start();
DefNewTracer gc_tracer;
gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
_next_gen = gch->next_gen(this);
// If the next generation is too full to accommodate promotion
// from this generation, pass on collection; let the next generation
// do it.
if (!collection_attempt_is_safe()) {
if (Verbose && PrintGCDetails) {
gclog_or_tty->print(" :: Collection attempt not safe :: ");
}
gch->set_incremental_collection_failed(); // Slight lie: we did not even attempt one
return;
}
assert(to()->is_empty(), "Else not collection_attempt_is_safe");
init_assuming_no_promotion_failure();
GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL);
// Capture heap used before collection (for printing).
size_t gch_prev_used = gch->used();
gch->trace_heap_before_gc(&gc_tracer);
SpecializationStats::clear();
// These can be shared for all code paths
IsAliveClosure is_alive(this);
ScanWeakRefClosure scan_weak_ref(this);
age_table()->clear();
to()->clear(SpaceDecorator::Mangle);
gch->rem_set()->prepare_for_younger_refs_iterate(false);
assert(gch->no_allocs_since_save_marks(0),
"save marks have not been newly set.");
// Not very pretty.
CollectorPolicy* cp = gch->collector_policy();
FastScanClosure fsc_with_no_gc_barrier(this, false);
FastScanClosure fsc_with_gc_barrier(this, true);
KlassScanClosure klass_scan_closure(&fsc_with_no_gc_barrier,
gch->rem_set()->klass_rem_set());
set_promo_failure_scan_stack_closure(&fsc_with_no_gc_barrier);
FastEvacuateFollowersClosure evacuate_followers(gch, _level, this,
&fsc_with_no_gc_barrier,
&fsc_with_gc_barrier);
assert(gch->no_allocs_since_save_marks(0),
"save marks have not been newly set.");
int so = SharedHeap::SO_AllClasses | SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
gch->gen_process_strong_roots(_level,
true, // Process younger gens, if any,
// as strong roots.
true, // activate StrongRootsScope
true, // is scavenging
SharedHeap::ScanningOption(so),
&fsc_with_no_gc_barrier,
true, // walk *all* scavengable nmethods
&fsc_with_gc_barrier,
&klass_scan_closure);
// "evacuate followers".
evacuate_followers.do_void();
FastKeepAliveClosure keep_alive(this, &scan_weak_ref);
ReferenceProcessor* rp = ref_processor();
rp->setup_policy(clear_all_soft_refs);
const ReferenceProcessorStats& stats =
rp->process_discovered_references(&is_alive, &keep_alive, &evacuate_followers,
NULL, _gc_timer);
gc_tracer.report_gc_reference_stats(stats);
if (!_promotion_failed) {
// Swap the survivor spaces.
eden()->clear(SpaceDecorator::Mangle);
from()->clear(SpaceDecorator::Mangle);
if (ZapUnusedHeapArea) {
// This is now done here because of the piece-meal mangling which
// can check for valid mangling at intermediate points in the
// collection(s). When a minor collection fails to collect
// sufficient space resizing of the young generation can occur
// an redistribute the spaces in the young generation. Mangle
// here so that unzapped regions don't get distributed to
// other spaces.
to()->mangle_unused_area();
}
swap_spaces();
assert(to()->is_empty(), "to space should be empty now");
adjust_desired_tenuring_threshold();
// A successful scavenge should restart the GC time limit count which is
// for full GC's.
AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy();
size_policy->reset_gc_overhead_limit_count();
if (PrintGC && !PrintGCDetails) {
gch->print_heap_change(gch_prev_used);
}
assert(!gch->incremental_collection_failed(), "Should be clear");
} else {
assert(_promo_failure_scan_stack.is_empty(), "post condition");
_promo_failure_scan_stack.clear(true); // Clear cached segments.
remove_forwarding_pointers();
if (PrintGCDetails) {
gclog_or_tty->print(" (promotion failed) ");
}
// Add to-space to the list of space to compact
// when a promotion failure has occurred. In that
// case there can be live objects in to-space
// as a result of a partial evacuation of eden
// and from-space.
swap_spaces(); // For uniformity wrt ParNewGeneration.
from()->set_next_compaction_space(to());
gch->set_incremental_collection_failed();
// Inform the next generation that a promotion failure occurred.
_next_gen->promotion_failure_occurred();
gc_tracer.report_promotion_failed(_promotion_failed_info);
// Reset the PromotionFailureALot counters.
NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();)
}
// set new iteration safe limit for the survivor spaces
from()->set_concurrent_iteration_safe_limit(from()->top());
to()->set_concurrent_iteration_safe_limit(to()->top());
SpecializationStats::print();
// 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);
gch->trace_heap_after_gc(&gc_tracer);
gc_tracer.report_tenuring_threshold(tenuring_threshold());
_gc_timer->register_gc_end();
gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
}