/* -*- 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 jsgc_root_h__ #define jsgc_root_h__ #include "mozilla/GuardObjects.h" #include "mozilla/TypeTraits.h" #include "js/Utility.h" #include "js/TemplateLib.h" #include "jspubtd.h" /* * Moving GC Stack Rooting * * A moving GC may change the physical location of GC allocated things, even * when they are rooted, updating all pointers to the thing to refer to its new * location. The GC must therefore know about all live pointers to a thing, * not just one of them, in order to behave correctly. * * The |Rooted| and |Handle| classes below are used to root stack locations * whose value may be held live across a call that can trigger GC. For a * code fragment such as: * * JSObject *obj = NewObject(cx); * DoSomething(cx); * ... = obj->lastProperty(); * * If |DoSomething()| can trigger a GC, the stack location of |obj| must be * rooted to ensure that the GC does not move the JSObject referred to by * |obj| without updating |obj|'s location itself. This rooting must happen * regardless of whether there are other roots which ensure that the object * itself will not be collected. * * If |DoSomething()| cannot trigger a GC, and the same holds for all other * calls made between |obj|'s definitions and its last uses, then no rooting * is required. * * SpiderMonkey can trigger a GC at almost any time and in ways that are not * always clear. For example, the following innocuous-looking actions can * cause a GC: allocation of any new GC thing; JSObject::hasProperty; * JS_ReportError and friends; and ToNumber, among many others. The following * dangerous-looking actions cannot trigger a GC: js_malloc, cx->malloc_, * rt->malloc_, and friends and JS_ReportOutOfMemory. * * The following family of three classes will exactly root a stack location. * Incorrect usage of these classes will result in a compile error in almost * all cases. Therefore, it is very hard to be incorrectly rooted if you use * these classes exclusively. These classes are all templated on the type T of * the value being rooted. * * - Rooted<T> declares a variable of type T, whose value is always rooted. * Rooted<T> may be automatically coerced to a Handle<T>, below. Rooted<T> * should be used whenever a local variable's value may be held live across a * call which can trigger a GC. * * - Handle<T> is a const reference to a Rooted<T>. Functions which take GC * things or values as arguments and need to root those arguments should * generally use handles for those arguments and avoid any explicit rooting. * This has two benefits. First, when several such functions call each other * then redundant rooting of multiple copies of the GC thing can be avoided. * Second, if the caller does not pass a rooted value a compile error will be * generated, which is quicker and easier to fix than when relying on a * separate rooting analysis. * * - MutableHandle<T> is a non-const reference to Rooted<T>. It is used in the * same way as Handle<T> and includes a |set(const T &v)| method to allow * updating the value of the referenced Rooted<T>. A MutableHandle<T> can be * created from a Rooted<T> by using |Rooted<T>::operator&()|. * * In some cases the small performance overhead of exact rooting (measured to * be a few nanoseconds on desktop) is too much. In these cases, try the * following: * * - Move all Rooted<T> above inner loops: this allows you to re-use the root * on each iteration of the loop. * * - Pass Handle<T> through your hot call stack to avoid re-rooting costs at * every invocation. * * The following diagram explains the list of supported, implicit type * conversions between classes of this family: * * Rooted<T> ----> Handle<T> * | ^ * | | * | | * +---> MutableHandle<T> * (via &) * * All of these types have an implicit conversion to raw pointers. */ namespace js { class Module; template <typename T> struct RootMethods {}; template <typename T> class RootedBase {}; template <typename T> class HandleBase {}; template <typename T> class MutableHandleBase {}; /* * js::NullPtr acts like a NULL pointer in contexts that require a Handle. * * Handle provides an implicit constructor for js::NullPtr so that, given: * foo(Handle<JSObject*> h); * callers can simply write: * foo(js::NullPtr()); * which avoids creating a Rooted<JSObject*> just to pass NULL. * * This is the SpiderMonkey internal variant. js::NullPtr should be used in * preference to JS::NullPtr to avoid the GOT access required for JS_PUBLIC_API * symbols. */ struct NullPtr { static void * const constNullValue; }; } /* namespace js */ namespace JS { template <typename T> class Rooted; template <typename T> class Handle; template <typename T> class MutableHandle; /* This is exposing internal state of the GC for inlining purposes. */ JS_FRIEND_API(bool) isGCEnabled(); #if defined(DEBUG) && defined(JS_GC_ZEAL) && defined(JSGC_ROOT_ANALYSIS) && !defined(JS_THREADSAFE) extern void CheckStackRoots(JSContext *cx); #endif /* * JS::NullPtr acts like a NULL pointer in contexts that require a Handle. * * Handle provides an implicit constructor for JS::NullPtr so that, given: * foo(Handle<JSObject*> h); * callers can simply write: * foo(JS::NullPtr()); * which avoids creating a Rooted<JSObject*> just to pass NULL. */ struct JS_PUBLIC_API(NullPtr) { static void * const constNullValue; }; /* * Reference to a T that has been rooted elsewhere. This is most useful * as a parameter type, which guarantees that the T lvalue is properly * rooted. See "Move GC Stack Rooting" above. * * If you want to add additional methods to Handle for a specific * specialization, define a HandleBase<T> specialization containing them. */ template <typename T> class MOZ_STACK_CLASS Handle : public js::HandleBase<T> { friend class MutableHandle<T>; public: /* Creates a handle from a handle of a type convertible to T. */ template <typename S> Handle(Handle<S> handle, typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy = 0) { ptr = reinterpret_cast<const T *>(handle.address()); } /* Create a handle for a NULL pointer. */ Handle(js::NullPtr) { MOZ_STATIC_ASSERT(mozilla::IsPointer<T>::value, "js::NullPtr overload not valid for non-pointer types"); ptr = reinterpret_cast<const T *>(&js::NullPtr::constNullValue); } /* Create a handle for a NULL pointer. */ Handle(JS::NullPtr) { MOZ_STATIC_ASSERT(mozilla::IsPointer<T>::value, "JS::NullPtr overload not valid for non-pointer types"); ptr = reinterpret_cast<const T *>(&JS::NullPtr::constNullValue); } Handle(MutableHandle<T> handle) { ptr = handle.address(); } /* * This may be called only if the location of the T is guaranteed * to be marked (for some reason other than being a Rooted), * e.g., if it is guaranteed to be reachable from an implicit root. * * Create a Handle from a raw location of a T. */ static Handle fromMarkedLocation(const T *p) { Handle h; h.ptr = p; return h; } /* * Construct a handle from an explicitly rooted location. This is the * normal way to create a handle, and normally happens implicitly. */ template <typename S> inline Handle(const Rooted<S> &root, typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy = 0); /* Construct a read only handle from a mutable handle. */ template <typename S> inline Handle(MutableHandle<S> &root, typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy = 0); const T *address() const { return ptr; } T get() const { return *ptr; } operator T() const { return get(); } T operator->() const { return get(); } bool operator!=(const T &other) { return *ptr != other; } bool operator==(const T &other) { return *ptr == other; } private: Handle() {} const T *ptr; template <typename S> void operator=(S v) MOZ_DELETE; }; typedef Handle<JSObject*> HandleObject; typedef Handle<js::Module*> HandleModule; typedef Handle<JSFunction*> HandleFunction; typedef Handle<JSScript*> HandleScript; typedef Handle<JSString*> HandleString; typedef Handle<jsid> HandleId; typedef Handle<Value> HandleValue; /* * Similar to a handle, but the underlying storage can be changed. This is * useful for outparams. * * If you want to add additional methods to MutableHandle for a specific * specialization, define a MutableHandleBase<T> specialization containing * them. */ template <typename T> class MOZ_STACK_CLASS MutableHandle : public js::MutableHandleBase<T> { public: inline MutableHandle(Rooted<T> *root); void set(T v) { JS_ASSERT(!js::RootMethods<T>::poisoned(v)); *ptr = v; } /* * This may be called only if the location of the T is guaranteed * to be marked (for some reason other than being a Rooted), * e.g., if it is guaranteed to be reachable from an implicit root. * * Create a MutableHandle from a raw location of a T. */ static MutableHandle fromMarkedLocation(T *p) { MutableHandle h; h.ptr = p; return h; } T *address() const { return ptr; } T get() const { return *ptr; } operator T() const { return get(); } T operator->() const { return get(); } private: MutableHandle() {} T *ptr; template <typename S> void operator=(S v) MOZ_DELETE; }; typedef MutableHandle<JSObject*> MutableHandleObject; typedef MutableHandle<JSFunction*> MutableHandleFunction; typedef MutableHandle<JSScript*> MutableHandleScript; typedef MutableHandle<JSString*> MutableHandleString; typedef MutableHandle<jsid> MutableHandleId; typedef MutableHandle<Value> MutableHandleValue; } /* namespace JS */ namespace js { /* * InternalHandle is a handle to an internal pointer into a gcthing. Use * InternalHandle when you have a pointer to a direct field of a gcthing, or * when you need a parameter type for something that *may* be a pointer to a * direct field of a gcthing. */ template <typename T> class InternalHandle {}; template <typename T> class InternalHandle<T*> { void * const *holder; size_t offset; public: /* * Create an InternalHandle using a Handle to the gcthing containing the * field in question, and a pointer to the field. */ template<typename H> InternalHandle(const JS::Handle<H> &handle, T *field) : holder((void**)handle.address()), offset(uintptr_t(field) - uintptr_t(handle.get())) {} /* * Create an InternalHandle to a field within a Rooted<>. */ template<typename R> InternalHandle(const JS::Rooted<R> &root, T *field) : holder((void**)root.address()), offset(uintptr_t(field) - uintptr_t(root.get())) {} T *get() const { return reinterpret_cast<T*>(uintptr_t(*holder) + offset); } const T &operator*() const { return *get(); } T *operator->() const { return get(); } static InternalHandle<T*> fromMarkedLocation(T *fieldPtr) { return InternalHandle(fieldPtr); } private: /* * Create an InternalHandle to something that is not a pointer to a * gcthing, and so does not need to be rooted in the first place. Use these * InternalHandles to pass pointers into functions that also need to accept * regular InternalHandles to gcthing fields. * * Make this private to prevent accidental misuse; this is only for * fromMarkedLocation(). */ InternalHandle(T *field) : holder(reinterpret_cast<void * const *>(&js::NullPtr::constNullValue)), offset(uintptr_t(field)) {} }; /* * By default, pointers should use the inheritance hierarchy to find their * ThingRootKind. Some pointer types are explicitly set in jspubtd.h so that * Rooted<T> may be used without the class definition being available. */ template <typename T> struct RootKind<T *> { static ThingRootKind rootKind() { return T::rootKind(); } }; template <typename T> struct RootMethods<T *> { static T *initial() { return NULL; } static ThingRootKind kind() { return RootKind<T *>::rootKind(); } static bool poisoned(T *v) { return JS::IsPoisonedPtr(v); } }; } /* namespace js */ namespace JS { /* * Local variable of type T whose value is always rooted. This is typically * used for local variables, or for non-rooted values being passed to a * function that requires a handle, e.g. Foo(Root<T>(cx, x)). * * If you want to add additional methods to Rooted for a specific * specialization, define a RootedBase<T> specialization containing them. */ template <typename T> class MOZ_STACK_CLASS Rooted : public js::RootedBase<T> { void init(JSContext *cxArg) { #if defined(JSGC_ROOT_ANALYSIS) || defined(JSGC_USE_EXACT_ROOTING) js::ContextFriendFields *cx = js::ContextFriendFields::get(cxArg); commonInit(cx->thingGCRooters); #endif } void init(js::PerThreadData *ptArg) { #if defined(JSGC_ROOT_ANALYSIS) || defined(JSGC_USE_EXACT_ROOTING) js::PerThreadDataFriendFields *pt = js::PerThreadDataFriendFields::get(ptArg); commonInit(pt->thingGCRooters); #endif } public: Rooted(JSContext *cx MOZ_GUARD_OBJECT_NOTIFIER_PARAM) : ptr(js::RootMethods<T>::initial()) { MOZ_GUARD_OBJECT_NOTIFIER_INIT; init(cx); } Rooted(JSContext *cx, T initial MOZ_GUARD_OBJECT_NOTIFIER_PARAM) : ptr(initial) { MOZ_GUARD_OBJECT_NOTIFIER_INIT; init(cx); } Rooted(js::PerThreadData *pt MOZ_GUARD_OBJECT_NOTIFIER_PARAM) : ptr(js::RootMethods<T>::initial()) { MOZ_GUARD_OBJECT_NOTIFIER_INIT; init(pt); } Rooted(js::PerThreadData *pt, T initial MOZ_GUARD_OBJECT_NOTIFIER_PARAM) : ptr(initial) { MOZ_GUARD_OBJECT_NOTIFIER_INIT; init(pt); } ~Rooted() { #if defined(JSGC_ROOT_ANALYSIS) || defined(JSGC_USE_EXACT_ROOTING) JS_ASSERT(*stack == reinterpret_cast<Rooted<void*>*>(this)); *stack = prev; #endif } #if defined(JSGC_ROOT_ANALYSIS) || defined(JSGC_USE_EXACT_ROOTING) Rooted<T> *previous() { return prev; } #endif operator T() const { return ptr; } T operator->() const { return ptr; } T *address() { return &ptr; } const T *address() const { return &ptr; } T &get() { return ptr; } const T &get() const { return ptr; } T &operator=(T value) { JS_ASSERT(!js::RootMethods<T>::poisoned(value)); ptr = value; return ptr; } T &operator=(const Rooted &value) { ptr = value; return ptr; } bool operator!=(const T &other) { return ptr != other; } bool operator==(const T &other) { return ptr == other; } private: void commonInit(Rooted<void*> **thingGCRooters) { #if defined(JSGC_ROOT_ANALYSIS) || defined(JSGC_USE_EXACT_ROOTING) js::ThingRootKind kind = js::RootMethods<T>::kind(); this->stack = &thingGCRooters[kind]; this->prev = *stack; *stack = reinterpret_cast<Rooted<void*>*>(this); JS_ASSERT(!js::RootMethods<T>::poisoned(ptr)); #endif } #if defined(JSGC_ROOT_ANALYSIS) || defined(JSGC_USE_EXACT_ROOTING) Rooted<void*> **stack, *prev; #endif #if defined(DEBUG) && defined(JS_GC_ZEAL) && defined(JSGC_ROOT_ANALYSIS) && !defined(JS_THREADSAFE) /* Has the rooting analysis ever scanned this Rooted's stack location? */ friend void JS::CheckStackRoots(JSContext*); bool scanned; #endif /* * |ptr| must be the last field in Rooted because the analysis treats all * Rooted as Rooted<void*> during the analysis. See bug 829372. */ T ptr; MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER Rooted(const Rooted &) MOZ_DELETE; }; #if !(defined(JSGC_ROOT_ANALYSIS) || defined(JSGC_USE_EXACT_ROOTING)) // Defined in vm/String.h. template <> class Rooted<JSStableString *>; #endif typedef Rooted<JSObject*> RootedObject; typedef Rooted<js::Module*> RootedModule; typedef Rooted<JSFunction*> RootedFunction; typedef Rooted<JSScript*> RootedScript; typedef Rooted<JSString*> RootedString; typedef Rooted<jsid> RootedId; typedef Rooted<JS::Value> RootedValue; } /* namespace JS */ namespace js { /* * Mark a stack location as a root for the rooting analysis, without actually * rooting it in release builds. This should only be used for stack locations * of GC things that cannot be relocated by a garbage collection, and that * are definitely reachable via another path. */ class SkipRoot { #if defined(DEBUG) && defined(JS_GC_ZEAL) && defined(JSGC_ROOT_ANALYSIS) && !defined(JS_THREADSAFE) SkipRoot **stack, *prev; const uint8_t *start; const uint8_t *end; template <typename T> void init(SkipRoot **head, const T *ptr, size_t count) { this->stack = head; this->prev = *stack; *stack = this; this->start = (const uint8_t *) ptr; this->end = this->start + (sizeof(T) * count); } public: template <typename T> SkipRoot(JSContext *cx, const T *ptr, size_t count = 1 MOZ_GUARD_OBJECT_NOTIFIER_PARAM) { init(&ContextFriendFields::get(cx)->skipGCRooters, ptr, count); MOZ_GUARD_OBJECT_NOTIFIER_INIT; } template <typename T> SkipRoot(js::PerThreadData *ptd, const T *ptr, size_t count = 1 MOZ_GUARD_OBJECT_NOTIFIER_PARAM) { PerThreadDataFriendFields *ptff = PerThreadDataFriendFields::get(ptd); init(&ptff->skipGCRooters, ptr, count); MOZ_GUARD_OBJECT_NOTIFIER_INIT; } ~SkipRoot() { JS_ASSERT(*stack == this); *stack = prev; } SkipRoot *previous() { return prev; } bool contains(const uint8_t *v, size_t len) { return v >= start && v + len <= end; } #else /* DEBUG && JSGC_ROOT_ANALYSIS */ public: template <typename T> SkipRoot(JSContext *cx, const T *ptr, size_t count = 1 MOZ_GUARD_OBJECT_NOTIFIER_PARAM) { MOZ_GUARD_OBJECT_NOTIFIER_INIT; } template <typename T> SkipRoot(PerThreadData *ptd, const T *ptr, size_t count = 1 MOZ_GUARD_OBJECT_NOTIFIER_PARAM) { MOZ_GUARD_OBJECT_NOTIFIER_INIT; } #endif /* DEBUG && JSGC_ROOT_ANALYSIS */ MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER }; /* Interface substitute for Rooted<T> which does not root the variable's memory. */ template <typename T> class FakeRooted : public RootedBase<T> { public: FakeRooted(JSContext *cx MOZ_GUARD_OBJECT_NOTIFIER_PARAM) : ptr(RootMethods<T>::initial()) { MOZ_GUARD_OBJECT_NOTIFIER_INIT; } FakeRooted(JSContext *cx, T initial MOZ_GUARD_OBJECT_NOTIFIER_PARAM) : ptr(initial) { MOZ_GUARD_OBJECT_NOTIFIER_INIT; } operator T() const { return ptr; } T operator->() const { return ptr; } T *address() { return &ptr; } const T *address() const { return &ptr; } T &get() { return ptr; } const T &get() const { return ptr; } T &operator=(T value) { JS_ASSERT(!RootMethods<T>::poisoned(value)); ptr = value; return ptr; } bool operator!=(const T &other) { return ptr != other; } bool operator==(const T &other) { return ptr == other; } private: T ptr; MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER FakeRooted(const FakeRooted &) MOZ_DELETE; }; /* Interface substitute for MutableHandle<T> which is not required to point to rooted memory. */ template <typename T> class FakeMutableHandle : public js::MutableHandleBase<T> { public: FakeMutableHandle(T *t) { ptr = t; } FakeMutableHandle(FakeRooted<T> *root) { ptr = root->address(); } void set(T v) { JS_ASSERT(!js::RootMethods<T>::poisoned(v)); *ptr = v; } T *address() const { return ptr; } T get() const { return *ptr; } operator T() const { return get(); } T operator->() const { return get(); } private: FakeMutableHandle() {} T *ptr; template <typename S> void operator=(S v) MOZ_DELETE; }; /* * Types for a variable that either should or shouldn't be rooted, depending on * the template parameter Rooted. Used for implementing functions that can * operate on either rooted or unrooted data. * * The toHandle() and toMutableHandle() functions are for calling functions * which require handle types and are only called in the CanGC case. These * allow the calling code to type check. */ enum AllowGC { NoGC = 0, CanGC = 1 }; template <typename T, AllowGC allowGC> class MaybeRooted { }; template <typename T> class MaybeRooted<T, CanGC> { public: typedef JS::Handle<T> HandleType; typedef JS::Rooted<T> RootType; typedef JS::MutableHandle<T> MutableHandleType; static inline JS::Handle<T> toHandle(HandleType v) { return v; } static inline JS::MutableHandle<T> toMutableHandle(MutableHandleType v) { return v; } }; template <typename T> class MaybeRooted<T, NoGC> { public: typedef T HandleType; typedef FakeRooted<T> RootType; typedef FakeMutableHandle<T> MutableHandleType; static inline JS::Handle<T> toHandle(HandleType v) { JS_NOT_REACHED("Bad conversion"); return JS::Handle<T>::fromMarkedLocation(NULL); } static inline JS::MutableHandle<T> toMutableHandle(MutableHandleType v) { JS_NOT_REACHED("Bad conversion"); return JS::MutableHandle<T>::fromMarkedLocation(NULL); } }; } /* namespace js */ namespace JS { template <typename T> template <typename S> inline Handle<T>::Handle(const Rooted<S> &root, typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy) { ptr = reinterpret_cast<const T *>(root.address()); } template <typename T> template <typename S> inline Handle<T>::Handle(MutableHandle<S> &root, typename mozilla::EnableIf<mozilla::IsConvertible<S, T>::value, int>::Type dummy) { ptr = reinterpret_cast<const T *>(root.address()); } template <typename T> inline MutableHandle<T>::MutableHandle(Rooted<T> *root) { ptr = root->address(); } } /* namespace JS */ namespace js { /* * Hook for dynamic root analysis. Checks the native stack and poisons * references to GC things which have not been rooted. */ inline void MaybeCheckStackRoots(JSContext *cx) { #if defined(DEBUG) && defined(JS_GC_ZEAL) && defined(JSGC_ROOT_ANALYSIS) && !defined(JS_THREADSAFE) JS::CheckStackRoots(cx); #endif } namespace gc { struct Cell; } /* namespace gc */ /* Base class for automatic read-only object rooting during compilation. */ class CompilerRootNode { protected: CompilerRootNode(js::gc::Cell *ptr) : next(NULL), ptr_(ptr) {} public: void **address() { return (void **)&ptr_; } public: CompilerRootNode *next; protected: js::gc::Cell *ptr_; }; } /* namespace js */ #endif /* jsgc_root_h___ */