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cppgc_helpers.h
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#ifndef SRC_CPPGC_HELPERS_H_
#define SRC_CPPGC_HELPERS_H_
#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
#include <type_traits> // std::remove_reference
#include "cppgc/garbage-collected.h"
#include "cppgc/name-provider.h"
#include "cppgc/persistent.h"
#include "memory_tracker.h"
#include "util.h"
#include "v8-cppgc.h"
#include "v8-sandbox.h"
#include "v8.h"
namespace node {
class Environment;
class Realm;
class CppgcWrapperListNode;
/**
* This is a helper mixin with a BaseObject-like interface to help
* implementing wrapper objects managed by V8's cppgc (Oilpan) library.
* cppgc-manged objects in Node.js internals should extend this mixin,
* while non-cppgc-managed objects typically extend BaseObject - the
* latter are being migrated to be cppgc-managed wherever it's beneficial
* and practical. Typically cppgc-managed objects are more efficient to
* keep track of (which lowers initialization cost) and work better
* with V8's GC scheduling.
*
* A cppgc-managed native wrapper should look something like this, note
* that per cppgc rules, CPPGC_MIXIN(MyWrap) must be at the left-most
* position in the hierarchy (which ensures cppgc::GarbageCollected
* is at the left-most position).
*
* class MyWrap final : CPPGC_MIXIN(MyWrap) {
* public:
* SET_CPPGC_NAME(MyWrap) // Sets the heap snapshot name to "Node / MyWrap"
* void Trace(cppgc::Visitor* visitor) const final {
* CppgcMixin::Trace(visitor);
* visitor->Trace(...); // Trace any additional owned traceable data
* }
* }
*
* If the wrapper needs to perform cleanups when it's destroyed and that
* cleanup relies on a living Node.js `Realm`, it should implement a
* pattern like this:
*
* ~MyWrap() { this->Destroy(); }
* void Clean(Realm* env) override {
* // Do cleanup that relies on a living Environemnt.
* }
*/
class CppgcMixin : public cppgc::GarbageCollectedMixin, public MemoryRetainer {
public:
// To help various callbacks access wrapper objects with different memory
// management, cppgc-managed objects share the same layout as BaseObjects.
enum InternalFields { kEmbedderType = 0, kSlot, kInternalFieldCount };
// The initialization cannot be done in the mixin constructor but has to be
// invoked from the child class constructor, per cppgc::GarbageCollectedMixin
// rules.
template <typename T>
static inline void Wrap(T* ptr, Realm* realm, v8::Local<v8::Object> obj);
template <typename T>
static inline void Wrap(T* ptr, Environment* env, v8::Local<v8::Object> obj);
inline v8::Local<v8::Object> object() const;
inline Environment* env() const;
inline Realm* realm() const { return realm_; }
inline v8::Local<v8::Object> object(v8::Isolate* isolate) const {
return traced_reference_.Get(isolate);
}
template <typename T>
static inline T* Unwrap(v8::Local<v8::Object> obj);
// Subclasses are expected to invoke CppgcMixin::Trace() in their own Trace()
// methods.
void Trace(cppgc::Visitor* visitor) const override {
visitor->Trace(traced_reference_);
}
// TODO(joyeecheung): use ObjectSizeTrait;
inline size_t SelfSize() const override { return sizeof(*this); }
inline bool IsCppgcWrapper() const override { return true; }
// This is run for all the remaining Cppgc wrappers tracked in the Realm
// during Realm shutdown. The destruction of the wrappers would happen later,
// when the final garbage collection is triggered when CppHeap is torn down as
// part of the Isolate teardown. If subclasses of CppgcMixin wish to perform
// cleanups that depend on the Realm during destruction, they should implment
// it in a Clean() override, and then call this->Finalize() from their
// destructor. Outside of Finalize(), subclasses should avoid calling
// into JavaScript or perform any operation that can trigger garbage
// collection during the destruction.
void Finalize() {
if (realm_ == nullptr) return;
this->Clean(realm_);
realm_ = nullptr;
}
// The default implementation of Clean() is a no-op. If subclasses wish
// to perform cleanup that require a living Realm, they should
// should put the cleanups in a Clean() override, and call this->Finalize()
// in the destructor, instead of doing those cleanups directly in the
// destructor.
virtual void Clean(Realm* realm) {}
inline ~CppgcMixin();
friend class CppgcWrapperListNode;
private:
Realm* realm_ = nullptr;
v8::TracedReference<v8::Object> traced_reference_;
};
// If the class doesn't have additional owned traceable data, use this macro to
// save the implementation of a custom Trace() method.
#define DEFAULT_CPPGC_TRACE() \
void Trace(cppgc::Visitor* visitor) const final { \
CppgcMixin::Trace(visitor); \
}
// This macro sets the node name in the heap snapshot with a "Node /" prefix.
// Classes that use this macro must extend cppgc::NameProvider.
#define SET_CPPGC_NAME(Klass) \
inline const char* GetHumanReadableName() const final { \
return "Node / " #Klass; \
}
4CE5
\
inline const char* MemoryInfoName() const override { return #Klass; }
/**
* Similar to ASSIGN_OR_RETURN_UNWRAP() but works on cppgc-managed types
* inheriting CppgcMixin.
*/
#define ASSIGN_OR_RETURN_UNWRAP_CPPGC(ptr, obj, ...) \
do { \
*ptr = CppgcMixin::Unwrap< \
typename std::remove_reference<decltype(**ptr)>::type>(obj); \
if (*ptr == nullptr) return __VA_ARGS__; \
} while (0)
} // namespace node
/**
* Helper macro the manage the cppgc-based wrapper hierarchy. This must
* be used at the left-most position - right after `:` in the class inheritance,
* like this:
* class Klass : CPPGC_MIXIN(Klass) ... {}
*
* This needs to disable linters because it will be at odds with
* clang-format.
*/
#define CPPGC_MIXIN(Klass) \
public /* NOLINT(whitespace/indent) */ \
v8::Object::Wrappable, public CppgcMixin
#endif // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
#endif // SRC_CPPGC_HELPERS_H_