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8375093: Convert GlobalCounter to use Atomic<T>

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Reviewed-by: dholmes, iwalulya
This commit is contained in:
Kim Barrett 2026-01-19 18:05:22 +00:00
parent f2d5290c29
commit 496af3cf47
5 changed files with 23 additions and 21 deletions
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5
src/hotspot/share/runtime/thread.cpp
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@ -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.
* Copyright (c) 2021, Azul Systems, Inc. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
@ -36,6 +36,7 @@
#include "memory/resourceArea.hpp"
#include "nmt/memTracker.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomic.hpp"
#include "runtime/atomicAccess.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/javaThread.inline.hpp"
@ -82,7 +83,7 @@ Thread::Thread(MemTag mem_tag) {
_threads_hazard_ptr = nullptr;
_threads_list_ptr = nullptr;
_nested_threads_hazard_ptr_cnt = 0;
_rcu_counter = 0;
_rcu_counter.store_relaxed(0);
// the handle mark links itself to last_handle_mark
new HandleMark(this);

7
src/hotspot/share/runtime/thread.hpp
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@ -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.
* Copyright (c) 2021, Azul Systems, Inc. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
@ -30,6 +30,7 @@
#include "gc/shared/threadLocalAllocBuffer.hpp"
#include "jni.h"
#include "memory/allocation.hpp"
#include "runtime/atomic.hpp"
#include "runtime/atomicAccess.hpp"
#include "runtime/globals.hpp"
#include "runtime/os.hpp"
@ -238,9 +239,9 @@ class Thread: public ThreadShadow {
// Support for GlobalCounter
private:
volatile uintx _rcu_counter;
Atomic<uintx> _rcu_counter;
public:
volatile uintx* get_rcu_counter() {
Atomic<uintx>* get_rcu_counter() {
return &_rcu_counter;
}

12
src/hotspot/share/utilities/globalCounter.cpp
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@ -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
@ -23,7 +23,7 @@
*/
#include "memory/iterator.hpp"
#include "runtime/atomicAccess.hpp"
#include "runtime/atomic.hpp"
#include "runtime/javaThread.hpp"
#include "runtime/threadSMR.inline.hpp"
#include "runtime/vmThread.hpp"
@ -41,7 +41,7 @@ class GlobalCounter::CounterThreadCheck : public ThreadClosure {
SpinYield yield;
// Loops on this thread until it has exited the critical read section.
while(true) {
uintx cnt = AtomicAccess::load_acquire(thread->get_rcu_counter());
uintx cnt = thread->get_rcu_counter()->load_acquire();
// This checks if the thread's counter is active. And if so is the counter
// for a pre-existing reader (belongs to this grace period). A pre-existing
// reader will have a lower counter than the global counter version for this
@ -57,9 +57,9 @@ class GlobalCounter::CounterThreadCheck : public ThreadClosure {
};
void GlobalCounter::write_synchronize() {
assert((*Thread::current()->get_rcu_counter() & COUNTER_ACTIVE) == 0x0, "must be outside a critcal section");
// AtomicAccess::add must provide fence since we have storeload dependency.
uintx gbl_cnt = AtomicAccess::add(&_global_counter._counter, COUNTER_INCREMENT);
assert((Thread::current()->get_rcu_counter()->load_relaxed() & COUNTER_ACTIVE) == 0x0, "must be outside a critcal section");
// Atomic add must provide fence since we have storeload dependency.
uintx gbl_cnt = _global_counter._counter.add_then_fetch(COUNTER_INCREMENT);
// Do all RCU threads.
CounterThreadCheck ctc(gbl_cnt);

5
src/hotspot/share/utilities/globalCounter.hpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2018, 2024, 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
@ -27,6 +27,7 @@
#include "memory/allStatic.hpp"
#include "memory/padded.hpp"
#include "runtime/atomic.hpp"
class Thread;
@ -47,7 +48,7 @@ class GlobalCounter : public AllStatic {
// counter is on a separate cacheline.
struct PaddedCounter {
DEFINE_PAD_MINUS_SIZE(0, DEFAULT_PADDING_SIZE, 0);
volatile uintx _counter;
Atomic<uintx> _counter;
DEFINE_PAD_MINUS_SIZE(1, DEFAULT_PADDING_SIZE, sizeof(volatile uintx));
};

15
src/hotspot/share/utilities/globalCounter.inline.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
@ -27,30 +27,29 @@
#include "utilities/globalCounter.hpp"
#include "runtime/atomicAccess.hpp"
#include "runtime/atomic.hpp"
#include "runtime/javaThread.hpp"
inline GlobalCounter::CSContext
GlobalCounter::critical_section_begin(Thread *thread) {
assert(thread == Thread::current(), "must be current thread");
uintx old_cnt = AtomicAccess::load(thread->get_rcu_counter());
uintx old_cnt = thread->get_rcu_counter()->load_relaxed();
// Retain the old counter value if already active, e.g. nested.
// Otherwise, set the counter to the current version + active bit.
uintx new_cnt = old_cnt;
if ((new_cnt & COUNTER_ACTIVE) == 0) {
new_cnt = AtomicAccess::load(&_global_counter._counter) | COUNTER_ACTIVE;
new_cnt = _global_counter._counter.load_relaxed() | COUNTER_ACTIVE;
}
AtomicAccess::release_store_fence(thread->get_rcu_counter(), new_cnt);
thread->get_rcu_counter()->release_store_fence(new_cnt);
return static_cast<CSContext>(old_cnt);
}
inline void
GlobalCounter::critical_section_end(Thread *thread, CSContext context) {
assert(thread == Thread::current(), "must be current thread");
assert((*thread->get_rcu_counter() & COUNTER_ACTIVE) == COUNTER_ACTIVE, "must be in critical section");
assert((thread->get_rcu_counter()->load_relaxed() & COUNTER_ACTIVE) == COUNTER_ACTIVE, "must be in critical section");
// Restore the counter value from before the associated begin.
AtomicAccess::release_store(thread->get_rcu_counter(),
static_cast<uintx>(context));
thread->get_rcu_counter()->release_store(static_cast<uintx>(context));
}
class GlobalCounter::CriticalSection {