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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=8 sts=4 et sw=4 tw=99:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef js_TraceKind_h
#define js_TraceKind_h
#include "mozilla/UniquePtr.h"
#include "js/TypeDecls.h"
// Forward declarations of all the types a TraceKind can denote.
namespace js {
class BaseShape;
class LazyScript;
class ObjectGroup;
class Shape;
class Scope;
namespace jit {
class JitCode;
} // namespace jit
} // namespace js
namespace JS {
// When tracing a thing, the GC needs to know about the layout of the object it
// is looking at. There are a fixed number of different layouts that the GC
// knows about. The "trace kind" is a static map which tells which layout a GC
// thing has.
//
// Although this map is public, the details are completely hidden. Not all of
// the matching C++ types are exposed, and those that are, are opaque.
//
// See Value::gcKind() and JSTraceCallback in Tracer.h for more details.
enum class TraceKind
{
// These trace kinds have a publicly exposed, although opaque, C++ type.
// Note: The order here is determined by our Value packing. Other users
// should sort alphabetically, for consistency.
Object = 0x00,
String = 0x02,
Symbol = 0x03,
// 0x1 is not used for any GCThing Value tag, so we use it for Script.
Script = 0x01,
// Shape details are exposed through JS_TraceShapeCycleCollectorChildren.
Shape = 0x04,
// ObjectGroup details are exposed through JS_TraceObjectGroupCycleCollectorChildren.
ObjectGroup = 0x05,
// The kind associated with a nullptr.
Null = 0x06,
// The following kinds do not have an exposed C++ idiom.
BaseShape = 0x0F,
JitCode = 0x1F,
LazyScript = 0x2F,
Scope = 0x3F
};
const static uintptr_t OutOfLineTraceKindMask = 0x07;
static_assert(uintptr_t(JS::TraceKind::BaseShape) & OutOfLineTraceKindMask, "mask bits are set");
static_assert(uintptr_t(JS::TraceKind::JitCode) & OutOfLineTraceKindMask, "mask bits are set");
static_assert(uintptr_t(JS::TraceKind::LazyScript) & OutOfLineTraceKindMask, "mask bits are set");
static_assert(uintptr_t(JS::TraceKind::Scope) & OutOfLineTraceKindMask, "mask bits are set");
// When this header is imported inside SpiderMonkey, the class definitions are
// available and we can query those definitions to find the correct kind
// directly from the class hierarchy.
template <typename T>
struct MapTypeToTraceKind {
static const JS::TraceKind kind = T::TraceKind;
};
// When this header is used outside SpiderMonkey, the class definitions are not
// available, so the following table containing all public GC types is used.
#define JS_FOR_EACH_TRACEKIND(D) \
/* PrettyName TypeName AddToCCKind */ \
D(BaseShape, js::BaseShape, true) \
D(JitCode, js::jit::JitCode, true) \
D(LazyScript, js::LazyScript, true) \
D(Scope, js::Scope, true) \
D(Object, JSObject, true) \
D(ObjectGroup, js::ObjectGroup, true) \
D(Script, JSScript, true) \
D(Shape, js::Shape, true) \
D(String, JSString, false) \
D(Symbol, JS::Symbol, false)
// Map from all public types to their trace kind.
#define JS_EXPAND_DEF(name, type, _) \
template <> struct MapTypeToTraceKind<type> { \
static const JS::TraceKind kind = JS::TraceKind::name; \
};
JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
#undef JS_EXPAND_DEF
// RootKind is closely related to TraceKind. Whereas TraceKind's indices are
// laid out for convenient embedding as a pointer tag, the indicies of RootKind
// are designed for use as array keys via EnumeratedArray.
enum class RootKind : int8_t
{
// These map 1:1 with trace kinds.
#define EXPAND_ROOT_KIND(name, _0, _1) \
name,
JS_FOR_EACH_TRACEKIND(EXPAND_ROOT_KIND)
#undef EXPAND_ROOT_KIND
// These tagged pointers are special-cased for performance.
Id,
Value,
// Everything else.
Traceable,
Limit
};
// Most RootKind correspond directly to a trace kind.
template <TraceKind traceKind> struct MapTraceKindToRootKind {};
#define JS_EXPAND_DEF(name, _0, _1) \
template <> struct MapTraceKindToRootKind<JS::TraceKind::name> { \
static const JS::RootKind kind = JS::RootKind::name; \
};
JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF)
#undef JS_EXPAND_DEF
// Specify the RootKind for all types. Value and jsid map to special cases;
// pointer types we can derive directly from the TraceKind; everything else
// should go in the Traceable list and use GCPolicy<T>::trace for tracing.
template <typename T>
struct MapTypeToRootKind {
static const JS::RootKind kind = JS::RootKind::Traceable;
};
template <typename T>
struct MapTypeToRootKind<T*> {
static const JS::RootKind kind =
JS::MapTraceKindToRootKind<JS::MapTypeToTraceKind<T>::kind>::kind;
};
template <typename T>
struct MapTypeToRootKind<mozilla::UniquePtr<T>> {
static const JS::RootKind kind = JS::MapTypeToRootKind<T>::kind;
};
template <> struct MapTypeToRootKind<JS::Value> {
static const JS::RootKind kind = JS::RootKind::Value;
};
template <> struct MapTypeToRootKind<jsid> {
static const JS::RootKind kind = JS::RootKind::Id;
};
template <> struct MapTypeToRootKind<JSFunction*> : public MapTypeToRootKind<JSObject*> {};
// Fortunately, few places in the system need to deal with fully abstract
// cells. In those places that do, we generally want to move to a layout
// templated function as soon as possible. This template wraps the upcast
// for that dispatch.
//
// Given a call:
//
// DispatchTraceKindTyped(f, thing, traceKind, ... args)
//
// Downcast the |void *thing| to the specific type designated by |traceKind|,
// and pass it to the functor |f| along with |... args|, forwarded. Pass the
// type designated by |traceKind| as the functor's template argument. The
// |thing| parameter is optional; without it, we simply pass through |... args|.
// GCC and Clang require an explicit template declaration in front of the
// specialization of operator() because it is a dependent template. MSVC, on
// the other hand, gets very confused if we have a |template| token there.
// The clang-cl front end defines _MSC_VER, but still requires the explicit
// template declaration, so we must test for __clang__ here as well.
#if defined(_MSC_VER) && !defined(__clang__)
# define JS_DEPENDENT_TEMPLATE_HINT
#else
# define JS_DEPENDENT_TEMPLATE_HINT template
#endif
template <typename F, typename... Args>
auto
DispatchTraceKindTyped(F f, JS::TraceKind traceKind, Args&&... args)
-> decltype(f. JS_DEPENDENT_TEMPLATE_HINT operator()<JSObject>(mozilla::Forward<Args>(args)...))
{
switch (traceKind) {
#define JS_EXPAND_DEF(name, type, _) \
case JS::TraceKind::name: \
return f. JS_DEPENDENT_TEMPLATE_HINT operator()<type>(mozilla::Forward<Args>(args)...);
JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
#undef JS_EXPAND_DEF
default:
MOZ_CRASH("Invalid trace kind in DispatchTraceKindTyped.");
}
}
#undef JS_DEPENDENT_TEMPLATE_HINT
template <typename F, typename... Args>
auto
DispatchTraceKindTyped(F f, void* thing, JS::TraceKind traceKind, Args&&... args)
-> decltype(f(static_cast<JSObject*>(nullptr), mozilla::Forward<Args>(args)...))
{
switch (traceKind) {
#define JS_EXPAND_DEF(name, type, _) \
case JS::TraceKind::name: \
return f(static_cast<type*>(thing), mozilla::Forward<Args>(args)...);
JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
#undef JS_EXPAND_DEF
default:
MOZ_CRASH("Invalid trace kind in DispatchTraceKindTyped.");
}
}
} // namespace JS
#endif // js_TraceKind_h
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