v8/include/cppgc/trace-trait.h
Omer Katz ab2b18e1be cppgc: Use object start bitmap to trace mixins
This CL removes the GetTraceDescriptor virtual call from garbage
collected mixins and replaces it with querying the object start
bitmap.

The CL also removes the mixin macros which are now no longer needed.

Bug: chromium:1056170
Change-Id: I27ed299f93025d09a3bb3f0d17b14bed3c200565
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2287508
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68787}
2020-07-10 12:00:45 +00:00

112 lines
2.8 KiB
C++

// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef INCLUDE_CPPGC_TRACE_TRAIT_H_
#define INCLUDE_CPPGC_TRACE_TRAIT_H_
#include <type_traits>
#include "cppgc/type-traits.h"
#include "v8config.h" // NOLINT(build/include_directory)
namespace cppgc {
class Visitor;
namespace internal {
// Implementation of the default TraceTrait handling GarbageCollected and
// GarbageCollectedMixin.
template <typename T,
bool =
IsGarbageCollectedMixinTypeV<typename std::remove_const<T>::type>>
struct TraceTraitImpl;
} // namespace internal
/**
* Callback for invoking tracing on a given object.
*
* \param visitor The visitor to dispatch to.
* \param object The object to invoke tracing on.
*/
using TraceCallback = void (*)(Visitor* visitor, const void* object);
/**
* Describes how to trace an object, i.e., how to visit all Oilpan-relevant
* fields of an object.
*/
struct TraceDescriptor {
/**
* Adjusted base pointer, i.e., the pointer to the class inheriting directly
* from GarbageCollected, of the object that is being traced.
*/
const void* base_object_payload;
/**
* Callback for tracing the object.
*/
TraceCallback callback;
};
namespace internal {
struct V8_EXPORT TraceTraitFromInnerAddressImpl {
static TraceDescriptor GetTraceDescriptor(const void* address);
};
} // namespace internal
/**
* Trait specifying how the garbage collector processes an object of type T.
*
* Advanced users may override handling by creating a specialization for their
* type.
*/
template <typename T>
struct TraceTrait {
static_assert(internal::IsTraceableV<T>, "T must have a Trace() method");
/**
* Accessor for retrieving a TraceDescriptor to process an object of type T.
*
* \param self The object to be processed.
* \returns a TraceDescriptor to process the object.
*/
static TraceDescriptor GetTraceDescriptor(const void* self) {
return internal::TraceTraitImpl<T>::GetTraceDescriptor(
static_cast<const T*>(self));
}
/**
* Function invoking the tracing for an object of type T.
*
* \param visitor The visitor to dispatch to.
* \param self The object to invoke tracing on.
*/
static void Trace(Visitor* visitor, const void* self) {
static_cast<const T*>(self)->Trace(visitor);
}
};
namespace internal {
template <typename T>
struct TraceTraitImpl<T, false> {
static TraceDescriptor GetTraceDescriptor(const void* self) {
return {self, TraceTrait<T>::Trace};
}
};
template <typename T>
struct TraceTraitImpl<T, true> {
static TraceDescriptor GetTraceDescriptor(const void* self) {
return internal::TraceTraitFromInnerAddressImpl::GetTraceDescriptor(self);
}
};
} // namespace internal
} // namespace cppgc
#endif // INCLUDE_CPPGC_TRACE_TRAIT_H_