root/src/objects-visiting.h
/* [<][>][^][v][top][bottom][index][help] */
DEFINITIONS
This source file includes following definitions.
- VISITOR_ID_LIST
// Copyright 2011 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#ifndef V8_OBJECTS_VISITING_H_
#define V8_OBJECTS_VISITING_H_
#include "allocation.h"
// This file provides base classes and auxiliary methods for defining
// static object visitors used during GC.
// Visiting HeapObject body with a normal ObjectVisitor requires performing
// two switches on object's instance type to determine object size and layout
// and one or more virtual method calls on visitor itself.
// Static visitor is different: it provides a dispatch table which contains
// pointers to specialized visit functions. Each map has the visitor_id
// field which contains an index of specialized visitor to use.
namespace v8 {
namespace internal {
// Base class for all static visitors.
class StaticVisitorBase : public AllStatic {
public:
#define VISITOR_ID_LIST(V) \
V(SeqAsciiString) \
V(SeqTwoByteString) \
V(ShortcutCandidate) \
V(ByteArray) \
V(FreeSpace) \
V(FixedArray) \
V(FixedDoubleArray) \
V(GlobalContext) \
V(DataObject2) \
V(DataObject3) \
V(DataObject4) \
V(DataObject5) \
V(DataObject6) \
V(DataObject7) \
V(DataObject8) \
V(DataObject9) \
V(DataObjectGeneric) \
V(JSObject2) \
V(JSObject3) \
V(JSObject4) \
V(JSObject5) \
V(JSObject6) \
V(JSObject7) \
V(JSObject8) \
V(JSObject9) \
V(JSObjectGeneric) \
V(Struct2) \
V(Struct3) \
V(Struct4) \
V(Struct5) \
V(Struct6) \
V(Struct7) \
V(Struct8) \
V(Struct9) \
V(StructGeneric) \
V(ConsString) \
V(SlicedString) \
V(Oddball) \
V(Code) \
V(Map) \
V(PropertyCell) \
V(SharedFunctionInfo) \
V(JSFunction) \
V(JSWeakMap) \
V(JSRegExp)
// For data objects, JS objects and structs along with generic visitor which
// can visit object of any size we provide visitors specialized by
// object size in words.
// Ids of specialized visitors are declared in a linear order (without
// holes) starting from the id of visitor specialized for 2 words objects
// (base visitor id) and ending with the id of generic visitor.
// Method GetVisitorIdForSize depends on this ordering to calculate visitor
// id of specialized visitor from given instance size, base visitor id and
// generic visitor's id.
enum VisitorId {
#define VISITOR_ID_ENUM_DECL(id) kVisit##id,
VISITOR_ID_LIST(VISITOR_ID_ENUM_DECL)
#undef VISITOR_ID_ENUM_DECL
kVisitorIdCount,
kVisitDataObject = kVisitDataObject2,
kVisitJSObject = kVisitJSObject2,
kVisitStruct = kVisitStruct2,
kMinObjectSizeInWords = 2
};
// Visitor ID should fit in one byte.
STATIC_ASSERT(kVisitorIdCount <= 256);
// Determine which specialized visitor should be used for given instance type
// and instance type.
static VisitorId GetVisitorId(int instance_type, int instance_size);
static VisitorId GetVisitorId(Map* map) {
return GetVisitorId(map->instance_type(), map->instance_size());
}
// For visitors that allow specialization by size calculate VisitorId based
// on size, base visitor id and generic visitor id.
static VisitorId GetVisitorIdForSize(VisitorId base,
VisitorId generic,
int object_size) {
ASSERT((base == kVisitDataObject) ||
(base == kVisitStruct) ||
(base == kVisitJSObject));
ASSERT(IsAligned(object_size, kPointerSize));
ASSERT(kMinObjectSizeInWords * kPointerSize <= object_size);
ASSERT(object_size < Page::kMaxNonCodeHeapObjectSize);
const VisitorId specialization = static_cast<VisitorId>(
base + (object_size >> kPointerSizeLog2) - kMinObjectSizeInWords);
return Min(specialization, generic);
}
};
template<typename Callback>
class VisitorDispatchTable {
public:
void CopyFrom(VisitorDispatchTable* other) {
// We are not using memcpy to guarantee that during update
// every element of callbacks_ array will remain correct
// pointer (memcpy might be implemented as a byte copying loop).
for (int i = 0; i < StaticVisitorBase::kVisitorIdCount; i++) {
NoBarrier_Store(&callbacks_[i], other->callbacks_[i]);
}
}
inline Callback GetVisitorById(StaticVisitorBase::VisitorId id) {
return reinterpret_cast<Callback>(callbacks_[id]);
}
inline Callback GetVisitor(Map* map) {
return reinterpret_cast<Callback>(callbacks_[map->visitor_id()]);
}
void Register(StaticVisitorBase::VisitorId id, Callback callback) {
ASSERT(id < StaticVisitorBase::kVisitorIdCount); // id is unsigned.
callbacks_[id] = reinterpret_cast<AtomicWord>(callback);
}
template<typename Visitor,
StaticVisitorBase::VisitorId base,
StaticVisitorBase::VisitorId generic,
int object_size_in_words>
void RegisterSpecialization() {
static const int size = object_size_in_words * kPointerSize;
Register(StaticVisitorBase::GetVisitorIdForSize(base, generic, size),
&Visitor::template VisitSpecialized<size>);
}
template<typename Visitor,
StaticVisitorBase::VisitorId base,
StaticVisitorBase::VisitorId generic>
void RegisterSpecializations() {
STATIC_ASSERT(
(generic - base + StaticVisitorBase::kMinObjectSizeInWords) == 10);
RegisterSpecialization<Visitor, base, generic, 2>();
RegisterSpecialization<Visitor, base, generic, 3>();
RegisterSpecialization<Visitor, base, generic, 4>();
RegisterSpecialization<Visitor, base, generic, 5>();
RegisterSpecialization<Visitor, base, generic, 6>();
RegisterSpecialization<Visitor, base, generic, 7>();
RegisterSpecialization<Visitor, base, generic, 8>();
RegisterSpecialization<Visitor, base, generic, 9>();
Register(generic, &Visitor::Visit);
}
private:
AtomicWord callbacks_[StaticVisitorBase::kVisitorIdCount];
};
template<typename StaticVisitor>
class BodyVisitorBase : public AllStatic {
public:
INLINE(static void IteratePointers(Heap* heap,
HeapObject* object,
int start_offset,
int end_offset)) {
Object** start_slot = reinterpret_cast<Object**>(object->address() +
start_offset);
Object** end_slot = reinterpret_cast<Object**>(object->address() +
end_offset);
StaticVisitor::VisitPointers(heap, start_slot, end_slot);
}
};
template<typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
class FlexibleBodyVisitor : public BodyVisitorBase<StaticVisitor> {
public:
static inline ReturnType Visit(Map* map, HeapObject* object) {
int object_size = BodyDescriptor::SizeOf(map, object);
BodyVisitorBase<StaticVisitor>::IteratePointers(
map->GetHeap(),
object,
BodyDescriptor::kStartOffset,
object_size);
return static_cast<ReturnType>(object_size);
}
template<int object_size>
static inline ReturnType VisitSpecialized(Map* map, HeapObject* object) {
ASSERT(BodyDescriptor::SizeOf(map, object) == object_size);
BodyVisitorBase<StaticVisitor>::IteratePointers(
map->GetHeap(),
object,
BodyDescriptor::kStartOffset,
object_size);
return static_cast<ReturnType>(object_size);
}
};
template<typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
class FixedBodyVisitor : public BodyVisitorBase<StaticVisitor> {
public:
static inline ReturnType Visit(Map* map, HeapObject* object) {
BodyVisitorBase<StaticVisitor>::IteratePointers(
map->GetHeap(),
object,
BodyDescriptor::kStartOffset,
BodyDescriptor::kEndOffset);
return static_cast<ReturnType>(BodyDescriptor::kSize);
}
};
// Base class for visitors used for a linear new space iteration.
// IterateBody returns size of visited object.
// Certain types of objects (i.e. Code objects) are not handled
// by dispatch table of this visitor because they cannot appear
// in the new space.
//
// This class is intended to be used in the following way:
//
// class SomeVisitor : public StaticNewSpaceVisitor<SomeVisitor> {
// ...
// }
//
// This is an example of Curiously recurring template pattern
// (see http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern).
// We use CRTP to guarantee aggressive compile time optimizations (i.e.
// inlining and specialization of StaticVisitor::VisitPointers methods).
template<typename StaticVisitor>
class StaticNewSpaceVisitor : public StaticVisitorBase {
public:
static void Initialize();
static inline int IterateBody(Map* map, HeapObject* obj) {
return table_.GetVisitor(map)(map, obj);
}
static inline void VisitPointers(Heap* heap, Object** start, Object** end) {
for (Object** p = start; p < end; p++) StaticVisitor::VisitPointer(heap, p);
}
private:
static inline int VisitJSFunction(Map* map, HeapObject* object) {
Heap* heap = map->GetHeap();
VisitPointers(heap,
HeapObject::RawField(object, JSFunction::kPropertiesOffset),
HeapObject::RawField(object, JSFunction::kCodeEntryOffset));
// Don't visit code entry. We are using this visitor only during scavenges.
VisitPointers(
heap,
HeapObject::RawField(object,
JSFunction::kCodeEntryOffset + kPointerSize),
HeapObject::RawField(object,
JSFunction::kNonWeakFieldsEndOffset));
return JSFunction::kSize;
}
static inline int VisitByteArray(Map* map, HeapObject* object) {
return reinterpret_cast<ByteArray*>(object)->ByteArraySize();
}
static inline int VisitFixedDoubleArray(Map* map, HeapObject* object) {
int length = reinterpret_cast<FixedDoubleArray*>(object)->length();
return FixedDoubleArray::SizeFor(length);
}
static inline int VisitJSObject(Map* map, HeapObject* object) {
return JSObjectVisitor::Visit(map, object);
}
static inline int VisitSeqAsciiString(Map* map, HeapObject* object) {
return SeqAsciiString::cast(object)->
SeqAsciiStringSize(map->instance_type());
}
static inline int VisitSeqTwoByteString(Map* map, HeapObject* object) {
return SeqTwoByteString::cast(object)->
SeqTwoByteStringSize(map->instance_type());
}
static inline int VisitFreeSpace(Map* map, HeapObject* object) {
return FreeSpace::cast(object)->Size();
}
class DataObjectVisitor {
public:
template<int object_size>
static inline int VisitSpecialized(Map* map, HeapObject* object) {
return object_size;
}
static inline int Visit(Map* map, HeapObject* object) {
return map->instance_size();
}
};
typedef FlexibleBodyVisitor<StaticVisitor,
StructBodyDescriptor,
int> StructVisitor;
typedef FlexibleBodyVisitor<StaticVisitor,
JSObject::BodyDescriptor,
int> JSObjectVisitor;
typedef int (*Callback)(Map* map, HeapObject* object);
static VisitorDispatchTable<Callback> table_;
};
template<typename StaticVisitor>
VisitorDispatchTable<typename StaticNewSpaceVisitor<StaticVisitor>::Callback>
StaticNewSpaceVisitor<StaticVisitor>::table_;
} } // namespace v8::internal
#endif // V8_OBJECTS_VISITING_H_