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cppgc: Thread safe JSMember

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Make all writes to JSMember.val_ atomic and atomically check for
emptiness in Trace.

Bug: chromium:1056170
Change-Id: Ia7034b9318df081aa61c9b6664903dd4f73402a5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2431569
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70309}
This commit is contained in:
Omer Katz 2020-10-02 18:28:57 +02:00 committed by Commit Bot
parent ff61743fb0
commit f6bc6b6d0b
2 changed files with 17 additions and 5 deletions
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18
include/v8-cppgc.h
View File

@ -14,6 +14,7 @@ namespace v8 {
class Isolate;
template <typename T>
class JSMember;
class JSVisitor;
namespace internal {
@ -49,11 +50,21 @@ class V8_EXPORT JSMemberBase {
inline JSMemberBase& CopyImpl(const JSMemberBase& other);
inline JSMemberBase& MoveImpl(JSMemberBase&& other);
void SetSlotThreadSafe(void* value) {
reinterpret_cast<std::atomic<void*>*>(&val_)->store(
value, std::memory_order_relaxed);
}
bool IsEmptyThreadSafe() const {
return reinterpret_cast<std::atomic<const void*> const*>(&val_)->load(
std::memory_order_relaxed) == nullptr;
}
// val_ points to a GlobalHandles node.
internal::Address* val_ = nullptr;
template <typename T>
friend class v8::JSMember;
friend class v8::JSVisitor;
friend class v8::internal::JSMemberBaseExtractor;
};
@ -79,7 +90,7 @@ JSMemberBase& JSMemberBase::MoveImpl(JSMemberBase&& other) {
void JSMemberBase::Reset() {
if (IsEmpty()) return;
Delete(val_);
val_ = nullptr;
SetSlotThreadSafe(nullptr);
}
} // namespace internal
@ -144,7 +155,8 @@ class V8_EXPORT JSMember : public internal::JSMemberBase {
typename = std::enable_if_t<std::is_base_of<T, U>::value>>
void Set(v8::Isolate* isolate, Local<U> that) {
Reset();
val_ = New(isolate, reinterpret_cast<internal::Address*>(*that), &val_);
SetSlotThreadSafe(
New(isolate, reinterpret_cast<internal::Address*>(*that), &val_));
}
};
@ -200,7 +212,7 @@ class JSVisitor : public cppgc::Visitor {
template <typename T>
void Trace(const JSMember<T>& ref) {
if (ref.IsEmpty()) return;
if (ref.IsEmptyThreadSafe()) return;
Visit(ref);
}

4
src/handles/global-handles.cc
View File

@ -1073,7 +1073,7 @@ void GlobalHandles::MoveTracedGlobal(Address** from, Address** to) {
}
}
DestroyTraced(*from);
*from = nullptr;
SetSlotThreadSafe(from, nullptr);
} else {
// Pure heap move.
DestroyTraced(*to);
@ -1086,7 +1086,7 @@ void GlobalHandles::MoveTracedGlobal(Address** from, Address** to) {
if (to_node->has_destructor()) {
to_node->set_parameter(to);
}
*from = nullptr;
SetSlotThreadSafe(from, nullptr);
}
TracedNode::Verify(global_handles, to);
}