void CardTableRS::invalidate_or_clear(Generation* gen, bool younger,
bool perm) {
GenCollectedHeap* gch = GenCollectedHeap::heap();
// For each generation gen (and younger and/or perm)
// invalidate the cards for the currently occupied part
// of that generation and clear the cards for the
// unoccupied part of the generation (if any, making use
// of that generation's prev_used_region to determine that
// region). No need to do anything for the youngest
// generation. Also see note#20040107.ysr above.
Generation* g = gen;
for(Generation* prev_gen = gch->prev_gen(g); prev_gen != NULL;
g = prev_gen, prev_gen = gch->prev_gen(g)) {
MemRegion used_mr = g->used_region();
MemRegion to_be_cleared_mr = g->prev_used_region().minus(used_mr);
if (!to_be_cleared_mr.is_empty()) {
clear(to_be_cleared_mr);
}
invalidate(used_mr);
if (!younger) break;
}
// Clear perm gen cards if asked to do so.
if (perm) {
g = gch->perm_gen();
MemRegion used_mr = g->used_region();
MemRegion to_be_cleared_mr = g->prev_used_region().minus(used_mr);
if (!to_be_cleared_mr.is_empty()) {
clear(to_be_cleared_mr);
}
invalidate(used_mr);
}
}
void CardTableRS::clear_into_younger(Generation* gen, bool clear_perm) {
GenCollectedHeap* gch = GenCollectedHeap::heap();
// Generations younger than gen have been evacuated. We can clear
// card table entries for gen (we know that it has no pointers
// to younger gens) and for those below. The card tables for
// the youngest gen need never be cleared, and those for perm gen
// will be cleared based on the parameter clear_perm.
// There's a bit of subtlety in the clear() and invalidate()
// methods that we exploit here and in invalidate_or_clear()
// below to avoid missing cards at the fringes. If clear() or
// invalidate() are changed in the future, this code should
// be revisited. 20040107.ysr
Generation* g = gen;
for(Generation* prev_gen = gch->prev_gen(g);
prev_gen != NULL;
g = prev_gen, prev_gen = gch->prev_gen(g)) {
MemRegion to_be_cleared_mr = g->prev_used_region();
clear(to_be_cleared_mr);
}
// Clear perm gen cards if asked to do so.
if (clear_perm) {
MemRegion to_be_cleared_mr = gch->perm_gen()->prev_used_region();
clear(to_be_cleared_mr);
}
}
void HeapInspection::heap_inspection() {
ResourceMark rm;
HeapWord* permgen_bottom = NULL;
if (Universe::heap()->kind() == CollectedHeap::GenCollectedHeap) {
GenCollectedHeap* gch = GenCollectedHeap::heap();
gch->gc_prologue(false /* !full */); // get any necessary locks
permgen_bottom = gch->perm_gen()->used_region().start();
} else {
return;
}
// Collect klass instance info
// Iterate over objects in the heap
KlassInfoTable cit(KlassInfoTable::cit_size, permgen_bottom);
RecordInstanceClosure ric(&cit);
Universe::heap()->object_iterate(&ric);
// Sort and print klass instance info
KlassInfoHisto histo("\n"
"num #instances #bytes class name\n"
"--------------------------------------",
KlassInfoHisto::histo_initial_size);
HistoClosure hc(&histo);
cit.iterate(&hc);
histo.sort();
histo.print_on(gclog_or_tty);
gclog_or_tty->flush();
if (Universe::heap()->kind() == CollectedHeap::GenCollectedHeap) {
GenCollectedHeap* gch = GenCollectedHeap::heap();
gch->gc_epilogue(false /* !full */); // release all acquired locks
}
}
/**
* 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");
}
)
static void print_contents() {
if (PrintSharedSpaces) {
GenCollectedHeap* gch = GenCollectedHeap::heap();
CompactingPermGenGen* gen = (CompactingPermGenGen*)gch->perm_gen();
// High level summary of the read-only space:
ClassifyObjectClosure coc;
tty->cr(); tty->print_cr("ReadOnly space:");
gen->ro_space()->object_iterate(&coc);
coc.print();
// High level summary of the read-write space:
coc.reset();
tty->cr(); tty->print_cr("ReadWrite space:");
gen->rw_space()->object_iterate(&coc);
coc.print();
// Reset counters
ClearAllocCountClosure cacc;
gen->ro_space()->object_iterate(&cacc);
gen->rw_space()->object_iterate(&cacc);
coc.reset();
// Lower level summary of the read-only space:
gen->ro_space()->object_iterate(&coc);
tty->cr(); tty->print_cr("ReadOnly space:");
ClassifyInstanceKlassClosure cikc;
gen->rw_space()->object_iterate(&cikc);
cikc.print();
// Reset counters
gen->ro_space()->object_iterate(&cacc);
gen->rw_space()->object_iterate(&cacc);
coc.reset();
// Lower level summary of the read-write space:
gen->rw_space()->object_iterate(&coc);
cikc.reset();
tty->cr(); tty->print_cr("ReadWrite space:");
gen->rw_space()->object_iterate(&cikc);
cikc.print();
}
}
void CompactingPermGenGen::serialize_oops(SerializeOopClosure* soc) {
int tag = 0;
soc->do_tag(--tag);
assert(!UseCompressedOops, "UseCompressedOops doesn't work with shared archive");
// Verify the sizes of various oops in the system.
soc->do_tag(sizeof(oopDesc));
soc->do_tag(sizeof(instanceOopDesc));
soc->do_tag(sizeof(methodOopDesc));
soc->do_tag(sizeof(constMethodOopDesc));
soc->do_tag(sizeof(methodDataOopDesc));
soc->do_tag(arrayOopDesc::base_offset_in_bytes(T_BYTE));
soc->do_tag(sizeof(constantPoolOopDesc));
soc->do_tag(sizeof(constantPoolCacheOopDesc));
soc->do_tag(objArrayOopDesc::base_offset_in_bytes());
soc->do_tag(typeArrayOopDesc::base_offset_in_bytes(T_BYTE));
soc->do_tag(sizeof(symbolOopDesc));
soc->do_tag(sizeof(klassOopDesc));
soc->do_tag(sizeof(markOopDesc));
soc->do_tag(sizeof(compiledICHolderOopDesc));
// Dump the block offset table entries.
GenCollectedHeap* gch = GenCollectedHeap::heap();
CompactingPermGenGen* pg = (CompactingPermGenGen*)gch->perm_gen();
pg->serialize_bts(soc);
soc->do_tag(--tag);
pg->ro_space()->serialize_block_offset_array_offsets(soc);
soc->do_tag(--tag);
pg->rw_space()->serialize_block_offset_array_offsets(soc);
soc->do_tag(--tag);
// Special case - this oop needed in oop->is_oop() assertions.
soc->do_ptr((void**)&Universe::_klassKlassObj);
soc->do_tag(--tag);
// Dump/restore miscellaneous oops.
Universe::oops_do(soc, true);
soc->do_tag(--tag);
vmSymbols::oops_do(soc, true);
soc->do_tag(--tag);
CodeCache::oops_do(soc);
soc->do_tag(--tag);
soc->do_tag(666);
}