/**
* 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 GenMarkSweep::invoke_at_safepoint(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");
set_ref_processor(rp);
rp->setup_policy(clear_all_softrefs);
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();
// Increment the invocation count
_total_invocations++;
// 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();
allocate_stacks();
mark_sweep_phase1(clear_all_softrefs);
mark_sweep_phase2();
// Don't add any more derived pointers during phase3
#if defined(COMPILER2) || INCLUDE_JVMCI
assert(DerivedPointerTable::is_active(), "Sanity");
DerivedPointerTable::set_active(false);
#endif
mark_sweep_phase3();
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 the young generation 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.
CardTableRS* rs = gch->rem_set();
Generation* old_gen = gch->old_gen();
// Clear/invalidate below make use of the "prev_used_regions" saved earlier.
if (gch->young_gen()->used() == 0) {
// We've evacuated the young generation.
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);
}
CodeCache::gc_epilogue();
JvmtiExport::gc_epilogue();
// refs processing: clean slate
set_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 currently is all the generations in the heap).
// 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;
gch->update_time_of_last_gc(now);
gch->trace_heap_after_gc(_gc_tracer);
}
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);
}