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8065358: Refactor G1s usage of save_marks and reduce related races

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Stop using save_marks in G1 related code and make setting the replacement field less racy.

Reviewed-by: brutisso, tschatzl
This commit is contained in:
Mikael Gerdin 2014-11-26 10:53:31 +01:00
parent d65f3c41b7
commit b5ef32af36
5 changed files with 54 additions and 50 deletions
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49
hotspot/src/share/vm/gc_implementation/g1/heapRegion.cpp
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@ -326,7 +326,7 @@ void HeapRegion::initialize(MemRegion mr, bool clear_space, bool mangle_space) {
hr_clear(false /*par*/, false /*clear_space*/);
set_top(bottom());
record_top_and_timestamp();
record_timestamp();
assert(mr.end() == orig_end(),
err_msg("Given region end address " PTR_FORMAT " should match exactly "
@ -416,9 +416,9 @@ oops_on_card_seq_iterate_careful(MemRegion mr,
// If we're within a stop-world GC, then we might look at a card in a
// GC alloc region that extends onto a GC LAB, which may not be
// parseable. Stop such at the "saved_mark" of the region.
// parseable. Stop such at the "scan_top" of the region.
if (g1h->is_gc_active()) {
mr = mr.intersection(used_region_at_save_marks());
mr = mr.intersection(MemRegion(bottom(), scan_top()));
} else {
mr = mr.intersection(used_region());
}
@ -969,7 +969,7 @@ void HeapRegion::prepare_for_compaction(CompactPoint* cp) {
void G1OffsetTableContigSpace::clear(bool mangle_space) {
set_top(bottom());
set_saved_mark_word(bottom());
_scan_top = bottom();
CompactibleSpace::clear(mangle_space);
reset_bot();
}
@ -1001,41 +1001,42 @@ HeapWord* G1OffsetTableContigSpace::cross_threshold(HeapWord* start,
return _offsets.threshold();
}
HeapWord* G1OffsetTableContigSpace::saved_mark_word() const {
HeapWord* G1OffsetTableContigSpace::scan_top() const {
G1CollectedHeap* g1h = G1CollectedHeap::heap();
assert( _gc_time_stamp <= g1h->get_gc_time_stamp(), "invariant" );
HeapWord* local_top = top();
OrderAccess::loadload();
if (_gc_time_stamp < g1h->get_gc_time_stamp()) {
const unsigned local_time_stamp = _gc_time_stamp;
assert(local_time_stamp <= g1h->get_gc_time_stamp(), "invariant");
if (local_time_stamp < g1h->get_gc_time_stamp()) {
return local_top;
} else {
return Space::saved_mark_word();
return _scan_top;
}
}
void G1OffsetTableContigSpace::record_top_and_timestamp() {
void G1OffsetTableContigSpace::record_timestamp() {
G1CollectedHeap* g1h = G1CollectedHeap::heap();
unsigned curr_gc_time_stamp = g1h->get_gc_time_stamp();
if (_gc_time_stamp < curr_gc_time_stamp) {
// The order of these is important, as another thread might be
// about to start scanning this region. If it does so after
// set_saved_mark and before _gc_time_stamp = ..., then the latter
// will be false, and it will pick up top() as the high water mark
// of region. If it does so after _gc_time_stamp = ..., then it
// will pick up the right saved_mark_word() as the high water mark
// of the region. Either way, the behavior will be correct.
Space::set_saved_mark_word(top());
OrderAccess::storestore();
// Setting the time stamp here tells concurrent readers to look at
// scan_top to know the maximum allowed address to look at.
// scan_top should be bottom for all regions except for the
// retained old alloc region which should have scan_top == top
HeapWord* st = _scan_top;
guarantee(st == _bottom || st == _top, "invariant");
_gc_time_stamp = curr_gc_time_stamp;
// No need to do another barrier to flush the writes above. If
// this is called in parallel with other threads trying to
// allocate into the region, the caller should call this while
// holding a lock and when the lock is released the writes will be
// flushed.
}
}
void G1OffsetTableContigSpace::record_retained_region() {
// scan_top is the maximum address where it's safe for the next gc to
// scan this region.
_scan_top = top();
}
void G1OffsetTableContigSpace::safe_object_iterate(ObjectClosure* blk) {
object_iterate(blk);
}
@ -1063,6 +1064,8 @@ G1OffsetTableContigSpace(G1BlockOffsetSharedArray* sharedOffsetArray,
void G1OffsetTableContigSpace::initialize(MemRegion mr, bool clear_space, bool mangle_space) {
CompactibleSpace::initialize(mr, clear_space, mangle_space);
_top = bottom();
_scan_top = bottom();
set_saved_mark_word(NULL);
reset_bot();
}