/* -*- 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