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cppgc: Make Trace methods const

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Bug: chromium:1056170
Change-Id: Ifc519559868d9c3099d309f75ba8faf2018a1578
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2154951
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67235}
This commit is contained in:
Omer Katz 2020-04-20 13:50:46 +02:00 committed by Commit Bot
parent 4dbb44609e
commit b246d341cd
8 changed files with 46 additions and 29 deletions
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32
include/cppgc/garbage-collected.h
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@ -40,21 +40,21 @@ class GarbageCollectedBase {
} // namespace internal
/**
* Base class for managed objects. Only descendent types of GarbageCollected can
* be constructed using MakeGarbageCollected. Must be inherited from as
* Base class for managed objects. Only descendent types of GarbageCollected
* can be constructed using MakeGarbageCollected. Must be inherited from as
* left-most base class.
*
* Types inheriting from GarbageCollected must provide a method of
* signature `void Trace(cppgc::Visitor*)` that dispatchs all managed pointers
* to the visitor and delegates to garbage-collected base classes. The method
* must be virtual if the type is not directly a child of GarbageCollected and
* marked as final.
* signature `void Trace(cppgc::Visitor*) const` that dispatchs all managed
* pointers to the visitor and delegates to garbage-collected base classes.
* The method must be virtual if the type is not directly a child of
* GarbageCollected and marked as final.
*
* \code
* // Example using final class.
* class FinalType final : public GarbageCollected<FinalType> {
* public:
* void Trace(cppgc::Visitor* visitor) {
* void Trace(cppgc::Visitor* visitor) const {
* // Dispatch using visitor->Trace(...);
* }
* };
@ -62,12 +62,12 @@ class GarbageCollectedBase {
* // Example using non-final base class.
* class NonFinalBase : public GarbageCollected<NonFinalBase> {
* public:
* virtual void Trace(cppgc::Visitor*) {}
* virtual void Trace(cppgc::Visitor*) const {}
* };
*
* class FinalChild final : public NonFinalBase {
* public:
* void Trace(cppgc::Visitor* visitor) final {
* void Trace(cppgc::Visitor* visitor) const final {
* // Dispatch using visitor->Trace(...);
* NonFinalBase::Trace(visitor);
* }
@ -88,14 +88,14 @@ class GarbageCollected : public internal::GarbageCollectedBase {
* directly but must be mixed into the inheritance hierarchy of a
* GarbageCollected object.
*
* Types inheriting from GarbageCollectedMixin must override a virtual method of
* signature `void Trace(cppgc::Visitor*)` that dispatchs all managed pointers
* to the visitor and delegates to base classes.
* Types inheriting from GarbageCollectedMixin must override a virtual method
* of signature `void Trace(cppgc::Visitor*) const` that dispatchs all managed
* pointers to the visitor and delegates to base classes.
*
* \code
* class Mixin : public GarbageCollectedMixin {
* public:
* void Trace(cppgc::Visitor* visitor) override {
* void Trace(cppgc::Visitor* visitor) const override {
* // Dispatch using visitor->Trace(...);
* }
* };
@ -119,7 +119,7 @@ class GarbageCollectedMixin : public internal::GarbageCollectedBase {
* This Trace method must be overriden by objects inheriting from
* GarbageCollectedMixin.
*/
virtual void Trace(cppgc::Visitor*) {}
virtual void Trace(cppgc::Visitor*) const {}
};
/**
@ -130,7 +130,7 @@ class GarbageCollectedMixin : public internal::GarbageCollectedBase {
* \code
* class Mixin : public GarbageCollectedMixin {
* public:
* void Trace(cppgc::Visitor* visitor) override {
* void Trace(cppgc::Visitor* visitor) const override {
* // Dispatch using visitor->Trace(...);
* }
* };
@ -138,7 +138,7 @@ class GarbageCollectedMixin : public internal::GarbageCollectedBase {
* class Foo : public GarbageCollected<Foo>, public Mixin {
* USING_GARBAGE_COLLECTED_MIXIN();
* public:
* void Trace(cppgc::Visitor* visitor) override {
* void Trace(cppgc::Visitor* visitor) const override {
* // Dispatch using visitor->Trace(...);
* Mixin::Trace(visitor);
* }

3
include/cppgc/trace-trait.h
View File

@ -41,8 +41,7 @@ struct TraceTrait {
}
static void Trace(Visitor* visitor, const void* self) {
// TODO(chromium:1056170): Remove const_cast when Trace() methods are const.
static_cast<T*>(const_cast<void*>(self))->Trace(visitor);
static_cast<const T*>(self)->Trace(visitor);
}
};

18
include/cppgc/type-traits.h
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@ -37,6 +37,16 @@ struct IsSubclassOfTemplate {
decltype(SubclassCheck(std::declval<T*>()))::value;
};
// IsTraceMethodConst is used to verify that all Trace methods are marked as
// const. It is equivalent to IsTraceable but for a non-const object.
template <typename T, typename = void>
struct IsTraceMethodConst : std::false_type {};
template <typename T>
struct IsTraceMethodConst<T, void_t<decltype(std::declval<const T>().Trace(
std::declval<Visitor*>()))>> : std::true_type {
};
template <typename T, typename = void>
struct IsTraceable : std::false_type {
static_assert(sizeof(T), "T must be fully defined");
@ -45,7 +55,13 @@ struct IsTraceable : std::false_type {
template <typename T>
struct IsTraceable<
T, void_t<decltype(std::declval<T>().Trace(std::declval<Visitor*>()))>>
: std::true_type {};
: std::true_type {
// All Trace methods should be marked as const. If an object of type
// 'T' is traceable then any object of type 'const T' should also
// be traceable.
static_assert(IsTraceMethodConst<T>(),
"Trace methods should be marked as const.");
};
template <typename T>
constexpr bool IsTraceableV = IsTraceable<T>::value;

6
test/unittests/heap/cppgc/garbage-collected_unittest.cc
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@ -25,7 +25,7 @@ class MergedMixins : public Mixin, public OtherMixin {
MERGE_GARBAGE_COLLECTED_MIXINS();
public:
void Trace(cppgc::Visitor* visitor) override {
void Trace(cppgc::Visitor* visitor) const override {
Mixin::Trace(visitor);
OtherMixin::Trace(visitor);
}
@ -34,7 +34,9 @@ class GCWithMergedMixins : public GCed, public MergedMixins {
USING_GARBAGE_COLLECTED_MIXIN();
public:
void Trace(cppgc::Visitor* visitor) override { MergedMixins::Trace(visitor); }
void Trace(cppgc::Visitor* visitor) const override {
MergedMixins::Trace(visitor);
}
};
class GarbageCollectedTestWithHeap

4
test/unittests/heap/cppgc/member_unittests.cc
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@ -20,10 +20,10 @@ namespace internal {
namespace {
struct GCed : GarbageCollected<GCed> {
virtual void Trace(cppgc::Visitor*) {}
virtual void Trace(cppgc::Visitor*) const {}
};
struct DerivedGCed : GCed {
void Trace(cppgc::Visitor* v) override { GCed::Trace(v); }
void Trace(cppgc::Visitor* v) const override { GCed::Trace(v); }
};
// Compile tests.

4
test/unittests/heap/cppgc/persistent_unittests.cc
View File

@ -22,12 +22,12 @@ namespace {
struct GCed : GarbageCollected<GCed> {
static size_t trace_call_count;
virtual void Trace(cppgc::Visitor*) { ++trace_call_count; }
virtual void Trace(cppgc::Visitor*) const { ++trace_call_count; }
};
size_t GCed::trace_call_count = 0;
struct DerivedGCed : GCed {
void Trace(cppgc::Visitor* v) override { GCed::Trace(v); }
void Trace(cppgc::Visitor* v) const override { GCed::Trace(v); }
};
template <template <typename> class PersistentType>

4
test/unittests/heap/cppgc/prefinalizer_unittests.cc
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@ -22,7 +22,7 @@ class GCed : public GarbageCollected<GCed> {
CPPGC_USING_PRE_FINALIZER(GCed, PreFinalizer);
public:
void Trace(Visitor*) {}
void Trace(Visitor*) const {}
void PreFinalizer() { ++prefinalizer_callcount; }
static size_t prefinalizer_callcount;
@ -175,7 +175,7 @@ class AllocatingPrefinalizer : public GarbageCollected<AllocatingPrefinalizer> {
public:
explicit AllocatingPrefinalizer(cppgc::Heap* heap) : heap_(heap) {}
void Trace(Visitor*) {}
void Trace(Visitor*) const {}
void PreFinalizer() { MakeGarbageCollected<GCed>(heap_); }
private:

4
test/unittests/heap/cppgc/visitor_unittest.cc
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@ -26,7 +26,7 @@ class GCed : public GarbageCollected<GCed> {
GCed() { trace_callcount = 0; }
virtual void Trace(cppgc::Visitor* visitor) { trace_callcount++; }
virtual void Trace(cppgc::Visitor* visitor) const { trace_callcount++; }
};
size_t GCed::trace_callcount;
@ -44,7 +44,7 @@ class GCedMixinApplication : public GCed,
USING_GARBAGE_COLLECTED_MIXIN();
public:
void Trace(cppgc::Visitor* visitor) override {
void Trace(cppgc::Visitor* visitor) const override {
GCed::Trace(visitor);
GCedMixin::Trace(visitor);
}