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Hi all,

  please review this conversions of `ContiguousSpace` to use `Atomic<T>`.

Testing: gha, tier1-5

Thanks,
  Thomas
This commit is contained in:
Thomas Schatzl 2026-01-22 18:48:38 +01:00
parent 025041ba04
commit 9ff4dd1325
4 changed files with 14 additions and 19 deletions
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12
src/hotspot/share/gc/shared/space.cpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1997, 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
@ -30,7 +30,6 @@
#include "memory/iterator.inline.hpp"
#include "memory/universe.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomicAccess.hpp"
#include "runtime/java.hpp"
#include "runtime/safepoint.hpp"
#include "utilities/align.hpp"
@ -69,7 +68,7 @@ void ContiguousSpace::clear(bool mangle_space) {
#ifndef PRODUCT
void ContiguousSpace::mangle_unused_area() {
mangle_unused_area(MemRegion(_top, _end));
mangle_unused_area(MemRegion(top(), _end));
}
void ContiguousSpace::mangle_unused_area(MemRegion mr) {
@ -128,11 +127,8 @@ inline HeapWord* ContiguousSpace::par_allocate_impl(size_t size) {
HeapWord* obj = top();
if (pointer_delta(end(), obj) >= size) {
HeapWord* new_top = obj + size;
HeapWord* result = AtomicAccess::cmpxchg(top_addr(), obj, new_top);
// result can be one of two:
// the old top value: the exchange succeeded
// otherwise: the new value of the top is returned.
if (result == obj) {
// Retry if we did not successfully updated the top pointers.
if (_top.compare_set(obj, new_top)) {
assert(is_object_aligned(obj) && is_object_aligned(new_top), "checking alignment");
return obj;
}

14
src/hotspot/share/gc/shared/space.hpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1997, 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
@ -32,6 +32,7 @@
#include "memory/iterator.hpp"
#include "memory/memRegion.hpp"
#include "oops/markWord.hpp"
#include "runtime/atomic.hpp"
#include "runtime/mutexLocker.hpp"
#include "utilities/align.hpp"
#include "utilities/macros.hpp"
@ -53,7 +54,7 @@ class ContiguousSpace: public CHeapObj<mtGC> {
private:
HeapWord* _bottom;
HeapWord* _end;
HeapWord* _top;
Atomic<HeapWord*> _top;
// Allocation helpers (return null if full).
inline HeapWord* allocate_impl(size_t word_size);
@ -64,12 +65,12 @@ public:
// Accessors
HeapWord* bottom() const { return _bottom; }
HeapWord* end() const { return _end; }
HeapWord* top() const { return _top; }
HeapWord* end() const { return _end; }
HeapWord* top() const { return _top.load_relaxed(); }
void set_bottom(HeapWord* value) { _bottom = value; }
void set_end(HeapWord* value) { _end = value; }
void set_top(HeapWord* value) { _top = value; }
void set_top(HeapWord* value) { _top.store_relaxed(value); }
// Testers
bool is_empty() const { return used() == 0; }
@ -121,9 +122,6 @@ public:
// Iteration
void object_iterate(ObjectClosure* blk);
// Addresses for inlined allocation
HeapWord** top_addr() { return &_top; }
// Debugging
void verify() const;
};

4
src/hotspot/share/gc/shared/vmStructs_gc.hpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2018, 2025, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2018, 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
@ -97,7 +97,7 @@
\
nonstatic_field(ContiguousSpace, _bottom, HeapWord*) \
nonstatic_field(ContiguousSpace, _end, HeapWord*) \
nonstatic_field(ContiguousSpace, _top, HeapWord*) \
nonstatic_field(ContiguousSpace, _top, Atomic<HeapWord*>) \
\
nonstatic_field(MemRegion, _start, HeapWord*) \
nonstatic_field(MemRegion, _word_size, size_t)

3
src/hotspot/share/runtime/vmStructs.cpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2000, 2025, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2000, 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
@ -901,6 +901,7 @@
/*****************************/ \
\
declare_toplevel_type(void*) \
declare_toplevel_type(Atomic<HeapWord*>) \
declare_toplevel_type(int*) \
declare_toplevel_type(char*) \
declare_toplevel_type(char**) \