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8374682: ZGC: Convert zLiveMap to use Atomic<T>

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Reviewed-by: stefank, tschatzl
This commit is contained in:
Axel Boldt-Christmas 2026-01-26 15:05:24 +00:00
parent 61b722d59a
commit 99b4e05d50
3 changed files with 20 additions and 21 deletions
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17
src/hotspot/share/gc/z/zLiveMap.cpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2015, 2025, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2015, 2026, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -27,7 +27,6 @@
#include "gc/z/zStat.hpp"
#include "gc/z/zUtils.hpp"
#include "logging/log.hpp"
#include "runtime/atomicAccess.hpp"
#include "utilities/debug.hpp"
#include "utilities/powerOfTwo.hpp"
#include "utilities/spinYield.hpp"
@ -60,18 +59,18 @@ void ZLiveMap::reset(ZGenerationId id) {
// Multiple threads can enter here, make sure only one of them
// resets the marking information while the others busy wait.
for (uint32_t seqnum = AtomicAccess::load_acquire(&_seqnum);
for (uint32_t seqnum = _seqnum.load_acquire();
seqnum != generation->seqnum();
seqnum = AtomicAccess::load_acquire(&_seqnum)) {
seqnum = _seqnum.load_acquire()) {
if (seqnum != seqnum_initializing) {
// No one has claimed initialization of the livemap yet
if (AtomicAccess::cmpxchg(&_seqnum, seqnum, seqnum_initializing) == seqnum) {
if (_seqnum.compare_set(seqnum, seqnum_initializing)) {
// This thread claimed the initialization
// Reset marking information
_live_bytes = 0;
_live_objects = 0;
_live_bytes.store_relaxed(0u);
_live_objects.store_relaxed(0u);
// Clear segment claimed/live bits
segment_live_bits().clear();
@ -81,13 +80,13 @@ void ZLiveMap::reset(ZGenerationId id) {
// a bit is about to be set for the first time.
initialize_bitmap();
assert(_seqnum == seqnum_initializing, "Invalid");
assert(_seqnum.load_relaxed() == seqnum_initializing, "Invalid");
// Make sure the newly reset marking information is ordered
// before the update of the page seqnum, such that when the
// up-to-date seqnum is load acquired, the bit maps will not
// contain stale information.
AtomicAccess::release_store(&_seqnum, generation->seqnum());
_seqnum.release_store(generation->seqnum());
break;
}
}

9
src/hotspot/share/gc/z/zLiveMap.hpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2015, 2025, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2015, 2026, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -28,6 +28,7 @@
#include "gc/z/zBitMap.hpp"
#include "gc/z/zGenerationId.hpp"
#include "memory/allocation.hpp"
#include "runtime/atomic.hpp"
class ObjectClosure;
@ -41,9 +42,9 @@ private:
const uint32_t _segment_size;
const int _segment_shift;
volatile uint32_t _seqnum;
volatile uint32_t _live_objects;
volatile size_t _live_bytes;
Atomic<uint32_t> _seqnum;
Atomic<uint32_t> _live_objects;
Atomic<size_t> _live_bytes;
BitMap::bm_word_t _segment_live_bits;
BitMap::bm_word_t _segment_claim_bits;
ZBitMap _bitmap;

15
src/hotspot/share/gc/z/zLiveMap.inline.hpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2015, 2025, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2015, 2026, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -31,24 +31,23 @@
#include "gc/z/zGeneration.inline.hpp"
#include "gc/z/zMark.hpp"
#include "gc/z/zUtils.inline.hpp"
#include "runtime/atomicAccess.hpp"
#include "utilities/bitMap.inline.hpp"
#include "utilities/debug.hpp"
inline void ZLiveMap::reset() {
_seqnum = 0;
_seqnum.store_relaxed(0u);
}
inline bool ZLiveMap::is_marked(ZGenerationId id) const {
return AtomicAccess::load_acquire(&_seqnum) == ZGeneration::generation(id)->seqnum();
return _seqnum.load_acquire() == ZGeneration::generation(id)->seqnum();
}
inline uint32_t ZLiveMap::live_objects() const {
return _live_objects;
return _live_objects.load_relaxed();
}
inline size_t ZLiveMap::live_bytes() const {
return _live_bytes;
return _live_bytes.load_relaxed();
}
inline const BitMapView ZLiveMap::segment_live_bits() const {
@ -116,8 +115,8 @@ inline bool ZLiveMap::set(ZGenerationId id, BitMap::idx_t index, bool finalizabl
}
inline void ZLiveMap::inc_live(uint32_t objects, size_t bytes) {
AtomicAccess::add(&_live_objects, objects);
AtomicAccess::add(&_live_bytes, bytes);
_live_objects.add_then_fetch(objects);
_live_bytes.add_then_fetch(bytes);
}
inline BitMap::idx_t ZLiveMap::segment_start(BitMap::idx_t segment) const {