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Diffstat (limited to 'js/public/RootingAPI.h')
| -rw-r--r-- | js/public/RootingAPI.h | 1609 |
1 files changed, 1609 insertions, 0 deletions
diff --git a/js/public/RootingAPI.h b/js/public/RootingAPI.h new file mode 100644 index 0000000000..471c72dc42 --- /dev/null +++ b/js/public/RootingAPI.h @@ -0,0 +1,1609 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- + * vim: set ts=8 sts=2 et sw=2 tw=80: + * 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_RootingAPI_h +#define js_RootingAPI_h + +#include "mozilla/Attributes.h" +#include "mozilla/DebugOnly.h" +#include "mozilla/EnumeratedArray.h" +#include "mozilla/LinkedList.h" +#include "mozilla/Maybe.h" + +#include <type_traits> +#include <utility> + +#include "jspubtd.h" + +#include "js/ComparisonOperators.h" // JS::detail::DefineComparisonOps +#include "js/GCAnnotations.h" +#include "js/GCPolicyAPI.h" +#include "js/GCTypeMacros.h" // JS_FOR_EACH_PUBLIC_{,TAGGED_}GC_POINTER_TYPE +#include "js/HashTable.h" +#include "js/HeapAPI.h" // StackKindCount +#include "js/ProfilingStack.h" +#include "js/Realm.h" +#include "js/Stack.h" // JS::NativeStackLimit +#include "js/TypeDecls.h" +#include "js/UniquePtr.h" + +/* + * [SMDOC] Stack Rooting + * + * 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 with an implicit cast from a Rooted<T>*. + * + * 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 Nursery; + +// The defaulted Enable parameter for the following two types is for restricting +// specializations with std::enable_if. +template <typename T, typename Enable = void> +struct BarrierMethods {}; + +template <typename Element, typename Wrapper, typename Enable = void> +class WrappedPtrOperations {}; + +template <typename Element, typename Wrapper> +class MutableWrappedPtrOperations + : public WrappedPtrOperations<Element, Wrapper> {}; + +template <typename T, typename Wrapper> +class RootedOperations : public MutableWrappedPtrOperations<T, Wrapper> {}; + +template <typename T, typename Wrapper> +class HandleOperations : public WrappedPtrOperations<T, Wrapper> {}; + +template <typename T, typename Wrapper> +class MutableHandleOperations : public MutableWrappedPtrOperations<T, Wrapper> { +}; + +template <typename T, typename Wrapper> +class HeapOperations : public MutableWrappedPtrOperations<T, Wrapper> {}; + +// Cannot use FOR_EACH_HEAP_ABLE_GC_POINTER_TYPE, as this would import too many +// macros into scope + +// Add a 2nd template parameter to allow conditionally enabling partial +// specializations via std::enable_if. +template <typename T, typename Enable = void> +struct IsHeapConstructibleType : public std::false_type {}; + +#define JS_DECLARE_IS_HEAP_CONSTRUCTIBLE_TYPE(T) \ + template <> \ + struct IsHeapConstructibleType<T> : public std::true_type {}; +JS_FOR_EACH_PUBLIC_GC_POINTER_TYPE(JS_DECLARE_IS_HEAP_CONSTRUCTIBLE_TYPE) +JS_FOR_EACH_PUBLIC_TAGGED_GC_POINTER_TYPE(JS_DECLARE_IS_HEAP_CONSTRUCTIBLE_TYPE) +// Note that JS_DECLARE_IS_HEAP_CONSTRUCTIBLE_TYPE is left defined, to allow +// declaring other types (eg from js/public/experimental/TypedData.h) to +// be used with Heap<>. + +namespace gc { +struct Cell; +} /* namespace gc */ + +// Important: Return a reference so passing a Rooted<T>, etc. to +// something that takes a |const T&| is not a GC hazard. +#define DECLARE_POINTER_CONSTREF_OPS(T) \ + operator const T&() const { return get(); } \ + const T& operator->() const { return get(); } + +// Assignment operators on a base class are hidden by the implicitly defined +// operator= on the derived class. Thus, define the operator= directly on the +// class as we would need to manually pass it through anyway. +#define DECLARE_POINTER_ASSIGN_OPS(Wrapper, T) \ + Wrapper<T>& operator=(const T& p) { \ + set(p); \ + return *this; \ + } \ + Wrapper<T>& operator=(T&& p) { \ + set(std::move(p)); \ + return *this; \ + } \ + Wrapper<T>& operator=(const Wrapper<T>& other) { \ + set(other.get()); \ + return *this; \ + } + +#define DELETE_ASSIGNMENT_OPS(Wrapper, T) \ + template <typename S> \ + Wrapper<T>& operator=(S) = delete; \ + Wrapper<T>& operator=(const Wrapper<T>&) = delete; + +#define DECLARE_NONPOINTER_ACCESSOR_METHODS(ptr) \ + const T* address() const { return &(ptr); } \ + const T& get() const { return (ptr); } + +#define DECLARE_NONPOINTER_MUTABLE_ACCESSOR_METHODS(ptr) \ + T* address() { return &(ptr); } \ + T& get() { return (ptr); } + +} /* namespace js */ + +namespace JS { + +JS_PUBLIC_API void HeapObjectPostWriteBarrier(JSObject** objp, JSObject* prev, + JSObject* next); +JS_PUBLIC_API void HeapStringPostWriteBarrier(JSString** objp, JSString* prev, + JSString* next); +JS_PUBLIC_API void HeapBigIntPostWriteBarrier(JS::BigInt** bip, + JS::BigInt* prev, + JS::BigInt* next); +JS_PUBLIC_API void HeapObjectWriteBarriers(JSObject** objp, JSObject* prev, + JSObject* next); +JS_PUBLIC_API void HeapStringWriteBarriers(JSString** objp, JSString* prev, + JSString* next); +JS_PUBLIC_API void HeapBigIntWriteBarriers(JS::BigInt** bip, JS::BigInt* prev, + JS::BigInt* next); +JS_PUBLIC_API void HeapScriptWriteBarriers(JSScript** objp, JSScript* prev, + JSScript* next); + +/** + * SafelyInitialized<T>::create() creates a safely-initialized |T|, suitable for + * use as a default value in situations requiring a safe but arbitrary |T| + * value. Implemented as a static method of a struct to allow partial + * specialization for subclasses via the Enable template parameter. + */ +template <typename T, typename Enable = void> +struct SafelyInitialized { + static T create() { + // This function wants to presume that |T()| -- which value-initializes a + // |T| per C++11 [expr.type.conv]p2 -- will produce a safely-initialized, + // safely-usable T that it can return. + +#if defined(XP_WIN) || defined(XP_MACOSX) || \ + (defined(XP_UNIX) && !defined(__clang__)) + + // That presumption holds for pointers, where value initialization produces + // a null pointer. + constexpr bool IsPointer = std::is_pointer_v<T>; + + // For classes and unions we *assume* that if |T|'s default constructor is + // non-trivial it'll initialize correctly. (This is unideal, but C++ + // doesn't offer a type trait indicating whether a class's constructor is + // user-defined, which better approximates our desired semantics.) + constexpr bool IsNonTriviallyDefaultConstructibleClassOrUnion = + (std::is_class_v<T> || + std::is_union_v<T>)&&!std::is_trivially_default_constructible_v<T>; + + static_assert(IsPointer || IsNonTriviallyDefaultConstructibleClassOrUnion, + "T() must evaluate to a safely-initialized T"); + +#endif + + return T(); + } +}; + +#ifdef JS_DEBUG +/** + * For generational GC, assert that an object is in the tenured generation as + * opposed to being in the nursery. + */ +extern JS_PUBLIC_API void AssertGCThingMustBeTenured(JSObject* obj); +extern JS_PUBLIC_API void AssertGCThingIsNotNurseryAllocable( + js::gc::Cell* cell); +#else +inline void AssertGCThingMustBeTenured(JSObject* obj) {} +inline void AssertGCThingIsNotNurseryAllocable(js::gc::Cell* cell) {} +#endif + +/** + * The Heap<T> class is a heap-stored reference to a JS GC thing for use outside + * the JS engine. All members of heap classes that refer to GC things should use + * Heap<T> (or possibly TenuredHeap<T>, described below). + * + * Heap<T> is an abstraction that hides some of the complexity required to + * maintain GC invariants for the contained reference. It uses operator + * overloading to provide a normal pointer interface, but adds barriers to + * notify the GC of changes. + * + * Heap<T> implements the following barriers: + * + * - Post-write barrier (necessary for generational GC). + * - Read barrier (necessary for incremental GC and cycle collector + * integration). + * + * Note Heap<T> does not have a pre-write barrier as used internally in the + * engine. The read barrier is used to mark anything read from a Heap<T> during + * an incremental GC. + * + * Heap<T> may be moved or destroyed outside of GC finalization and hence may be + * used in dynamic storage such as a Vector. + * + * Heap<T> instances must be traced when their containing object is traced to + * keep the pointed-to GC thing alive. + * + * Heap<T> objects should only be used on the heap. GC references stored on the + * C/C++ stack must use Rooted/Handle/MutableHandle instead. + * + * Type T must be a public GC pointer type. + */ +template <typename T> +class MOZ_NON_MEMMOVABLE Heap : public js::HeapOperations<T, Heap<T>> { + // Please note: this can actually also be used by nsXBLMaybeCompiled<T>, for + // legacy reasons. + static_assert(js::IsHeapConstructibleType<T>::value, + "Type T must be a public GC pointer type"); + + public: + using ElementType = T; + + Heap() : ptr(SafelyInitialized<T>::create()) { + // No barriers are required for initialization to the default value. + static_assert(sizeof(T) == sizeof(Heap<T>), + "Heap<T> must be binary compatible with T."); + } + explicit Heap(const T& p) : ptr(p) { + postWriteBarrier(SafelyInitialized<T>::create(), ptr); + } + + /* + * For Heap, move semantics are equivalent to copy semantics. However, we want + * the copy constructor to be explicit, and an explicit move constructor + * breaks common usage of move semantics, so we need to define both, even + * though they are equivalent. + */ + explicit Heap(const Heap<T>& other) : ptr(other.getWithoutExpose()) { + postWriteBarrier(SafelyInitialized<T>::create(), ptr); + } + Heap(Heap<T>&& other) : ptr(other.getWithoutExpose()) { + postWriteBarrier(SafelyInitialized<T>::create(), ptr); + } + + Heap& operator=(Heap<T>&& other) { + set(other.getWithoutExpose()); + other.set(SafelyInitialized<T>::create()); + return *this; + } + + ~Heap() { postWriteBarrier(ptr, SafelyInitialized<T>::create()); } + + DECLARE_POINTER_CONSTREF_OPS(T); + DECLARE_POINTER_ASSIGN_OPS(Heap, T); + + const T* address() const { return &ptr; } + + void exposeToActiveJS() const { js::BarrierMethods<T>::exposeToJS(ptr); } + + const T& get() const { + exposeToActiveJS(); + return ptr; + } + const T& getWithoutExpose() const { + js::BarrierMethods<T>::readBarrier(ptr); + return ptr; + } + const T& unbarrieredGet() const { return ptr; } + + void set(const T& newPtr) { + T tmp = ptr; + ptr = newPtr; + postWriteBarrier(tmp, ptr); + } + + T* unsafeGet() { return &ptr; } + + void unbarrieredSet(const T& newPtr) { ptr = newPtr; } + + explicit operator bool() const { + return bool(js::BarrierMethods<T>::asGCThingOrNull(ptr)); + } + explicit operator bool() { + return bool(js::BarrierMethods<T>::asGCThingOrNull(ptr)); + } + + private: + void postWriteBarrier(const T& prev, const T& next) { + js::BarrierMethods<T>::postWriteBarrier(&ptr, prev, next); + } + + T ptr; +}; + +namespace detail { + +template <typename T> +struct DefineComparisonOps<Heap<T>> : std::true_type { + static const T& get(const Heap<T>& v) { return v.unbarrieredGet(); } +}; + +} // namespace detail + +static MOZ_ALWAYS_INLINE bool ObjectIsTenured(JSObject* obj) { + return !js::gc::IsInsideNursery(reinterpret_cast<js::gc::Cell*>(obj)); +} + +static MOZ_ALWAYS_INLINE bool ObjectIsTenured(const Heap<JSObject*>& obj) { + return ObjectIsTenured(obj.unbarrieredGet()); +} + +static MOZ_ALWAYS_INLINE bool ObjectIsMarkedGray(JSObject* obj) { + auto cell = reinterpret_cast<js::gc::Cell*>(obj); + if (js::gc::IsInsideNursery(cell)) { + return false; + } + + auto tenuredCell = reinterpret_cast<js::gc::TenuredCell*>(cell); + return js::gc::detail::CellIsMarkedGrayIfKnown(tenuredCell); +} + +static MOZ_ALWAYS_INLINE bool ObjectIsMarkedGray( + const JS::Heap<JSObject*>& obj) { + return ObjectIsMarkedGray(obj.unbarrieredGet()); +} + +// The following *IsNotGray functions take account of the eventual +// gray marking state at the end of any ongoing incremental GC by +// delaying the checks if necessary. + +#ifdef DEBUG + +inline void AssertCellIsNotGray(const js::gc::Cell* maybeCell) { + if (maybeCell) { + js::gc::detail::AssertCellIsNotGray(maybeCell); + } +} + +inline void AssertObjectIsNotGray(JSObject* maybeObj) { + AssertCellIsNotGray(reinterpret_cast<js::gc::Cell*>(maybeObj)); +} + +inline void AssertObjectIsNotGray(const JS::Heap<JSObject*>& obj) { + AssertObjectIsNotGray(obj.unbarrieredGet()); +} + +#else + +inline void AssertCellIsNotGray(js::gc::Cell* maybeCell) {} +inline void AssertObjectIsNotGray(JSObject* maybeObj) {} +inline void AssertObjectIsNotGray(const JS::Heap<JSObject*>& obj) {} + +#endif + +/** + * The TenuredHeap<T> class is similar to the Heap<T> class above in that it + * encapsulates the GC concerns of an on-heap reference to a JS object. However, + * it has two important differences: + * + * 1) Pointers which are statically known to only reference "tenured" objects + * can avoid the extra overhead of SpiderMonkey's write barriers. + * + * 2) Objects in the "tenured" heap have stronger alignment restrictions than + * those in the "nursery", so it is possible to store flags in the lower + * bits of pointers known to be tenured. TenuredHeap wraps a normal tagged + * pointer with a nice API for accessing the flag bits and adds various + * assertions to ensure that it is not mis-used. + * + * GC things are said to be "tenured" when they are located in the long-lived + * heap: e.g. they have gained tenure as an object by surviving past at least + * one GC. For performance, SpiderMonkey allocates some things which are known + * to normally be long lived directly into the tenured generation; for example, + * global objects. Additionally, SpiderMonkey does not visit individual objects + * when deleting non-tenured objects, so object with finalizers are also always + * tenured; for instance, this includes most DOM objects. + * + * The considerations to keep in mind when using a TenuredHeap<T> vs a normal + * Heap<T> are: + * + * - It is invalid for a TenuredHeap<T> to refer to a non-tenured thing. + * - It is however valid for a Heap<T> to refer to a tenured thing. + * - It is not possible to store flag bits in a Heap<T>. + */ +template <typename T> +class TenuredHeap : public js::HeapOperations<T, TenuredHeap<T>> { + public: + using ElementType = T; + + TenuredHeap() : bits(0) { + static_assert(sizeof(T) == sizeof(TenuredHeap<T>), + "TenuredHeap<T> must be binary compatible with T."); + } + explicit TenuredHeap(T p) : bits(0) { setPtr(p); } + explicit TenuredHeap(const TenuredHeap<T>& p) : bits(0) { + setPtr(p.getPtr()); + } + + void setPtr(T newPtr) { + MOZ_ASSERT((reinterpret_cast<uintptr_t>(newPtr) & flagsMask) == 0); + MOZ_ASSERT(js::gc::IsCellPointerValidOrNull(newPtr)); + if (newPtr) { + AssertGCThingMustBeTenured(newPtr); + } + bits = (bits & flagsMask) | reinterpret_cast<uintptr_t>(newPtr); + } + + void setFlags(uintptr_t flagsToSet) { + MOZ_ASSERT((flagsToSet & ~flagsMask) == 0); + bits |= flagsToSet; + } + + void unsetFlags(uintptr_t flagsToUnset) { + MOZ_ASSERT((flagsToUnset & ~flagsMask) == 0); + bits &= ~flagsToUnset; + } + + bool hasFlag(uintptr_t flag) const { + MOZ_ASSERT((flag & ~flagsMask) == 0); + return (bits & flag) != 0; + } + + T unbarrieredGetPtr() const { return reinterpret_cast<T>(bits & ~flagsMask); } + uintptr_t getFlags() const { return bits & flagsMask; } + + void exposeToActiveJS() const { + js::BarrierMethods<T>::exposeToJS(unbarrieredGetPtr()); + } + T getPtr() const { + exposeToActiveJS(); + return unbarrieredGetPtr(); + } + + operator T() const { return getPtr(); } + T operator->() const { return getPtr(); } + + explicit operator bool() const { + return bool(js::BarrierMethods<T>::asGCThingOrNull(unbarrieredGetPtr())); + } + explicit operator bool() { + return bool(js::BarrierMethods<T>::asGCThingOrNull(unbarrieredGetPtr())); + } + + TenuredHeap<T>& operator=(T p) { + setPtr(p); + return *this; + } + + TenuredHeap<T>& operator=(const TenuredHeap<T>& other) { + bits = other.bits; + return *this; + } + + private: + enum { + maskBits = 3, + flagsMask = (1 << maskBits) - 1, + }; + + uintptr_t bits; +}; + +namespace detail { + +template <typename T> +struct DefineComparisonOps<TenuredHeap<T>> : std::true_type { + static const T get(const TenuredHeap<T>& v) { return v.unbarrieredGetPtr(); } +}; + +} // namespace detail + +// std::swap uses a stack temporary, which prevents classes like Heap<T> +// from being declared MOZ_HEAP_CLASS. +template <typename T> +void swap(TenuredHeap<T>& aX, TenuredHeap<T>& aY) { + T tmp = aX; + aX = aY; + aY = tmp; +} + +template <typename T> +void swap(Heap<T>& aX, Heap<T>& aY) { + T tmp = aX; + aX = aY; + aY = tmp; +} + +static MOZ_ALWAYS_INLINE bool ObjectIsMarkedGray( + const JS::TenuredHeap<JSObject*>& obj) { + return ObjectIsMarkedGray(obj.unbarrieredGetPtr()); +} + +template <typename T> +class MutableHandle; +template <typename T> +class Rooted; +template <typename T> +class PersistentRooted; + +/** + * 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 HandleOperations<T> specialization containing them. + */ +template <typename T> +class MOZ_NONHEAP_CLASS Handle : public js::HandleOperations<T, Handle<T>> { + friend class MutableHandle<T>; + + public: + using ElementType = T; + + Handle(const Handle<T>&) = default; + + /* Creates a handle from a handle of a type convertible to T. */ + template <typename S> + MOZ_IMPLICIT Handle( + Handle<S> handle, + std::enable_if_t<std::is_convertible_v<S, T>, int> dummy = 0) { + static_assert(sizeof(Handle<T>) == sizeof(T*), + "Handle must be binary compatible with T*."); + ptr = reinterpret_cast<const T*>(handle.address()); + } + + MOZ_IMPLICIT Handle(decltype(nullptr)) { + static_assert(std::is_pointer_v<T>, + "nullptr_t overload not valid for non-pointer types"); + static void* const ConstNullValue = nullptr; + ptr = reinterpret_cast<const T*>(&ConstNullValue); + } + + MOZ_IMPLICIT Handle(MutableHandle<T> handle) { ptr = handle.address(); } + + /* + * Take care when calling this method! + * + * This creates a Handle from the raw location of a T. + * + * It should be called only if the following conditions hold: + * + * 1) 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. + * + * 2) the contents of the location are immutable, or at least cannot change + * for the lifetime of the handle, as its users may not expect its value + * to change underneath them. + */ + static constexpr Handle fromMarkedLocation(const T* p) { + return Handle(p, DeliberatelyChoosingThisOverload, + ImUsingThisOnlyInFromFromMarkedLocation); + } + + /* + * 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 MOZ_IMPLICIT Handle( + const Rooted<S>& root, + std::enable_if_t<std::is_convertible_v<S, T>, int> dummy = 0); + + template <typename S> + inline MOZ_IMPLICIT Handle( + const PersistentRooted<S>& root, + std::enable_if_t<std::is_convertible_v<S, T>, int> dummy = 0); + + /* Construct a read only handle from a mutable handle. */ + template <typename S> + inline MOZ_IMPLICIT Handle( + MutableHandle<S>& root, + std::enable_if_t<std::is_convertible_v<S, T>, int> dummy = 0); + + DECLARE_POINTER_CONSTREF_OPS(T); + DECLARE_NONPOINTER_ACCESSOR_METHODS(*ptr); + + private: + Handle() = default; + DELETE_ASSIGNMENT_OPS(Handle, T); + + enum Disambiguator { DeliberatelyChoosingThisOverload = 42 }; + enum CallerIdentity { ImUsingThisOnlyInFromFromMarkedLocation = 17 }; + constexpr Handle(const T* p, Disambiguator, CallerIdentity) : ptr(p) {} + + const T* ptr; +}; + +namespace detail { + +template <typename T> +struct DefineComparisonOps<Handle<T>> : std::true_type { + static const T& get(const Handle<T>& v) { return v.get(); } +}; + +} // namespace detail + +/** + * 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 MutableHandleOperations<T> specialization containing + * them. + */ +template <typename T> +class MOZ_STACK_CLASS MutableHandle + : public js::MutableHandleOperations<T, MutableHandle<T>> { + public: + using ElementType = T; + + inline MOZ_IMPLICIT MutableHandle(Rooted<T>* root); + inline MOZ_IMPLICIT MutableHandle(PersistentRooted<T>* root); + + private: + // Disallow nullptr for overloading purposes. + MutableHandle(decltype(nullptr)) = delete; + + public: + MutableHandle(const MutableHandle<T>&) = default; + void set(const T& v) { + *ptr = v; + MOZ_ASSERT(GCPolicy<T>::isValid(*ptr)); + } + void set(T&& v) { + *ptr = std::move(v); + MOZ_ASSERT(GCPolicy<T>::isValid(*ptr)); + } + + /* + * 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; + } + + DECLARE_POINTER_CONSTREF_OPS(T); + DECLARE_NONPOINTER_ACCESSOR_METHODS(*ptr); + DECLARE_NONPOINTER_MUTABLE_ACCESSOR_METHODS(*ptr); + + private: + MutableHandle() = default; + DELETE_ASSIGNMENT_OPS(MutableHandle, T); + + T* ptr; +}; + +namespace detail { + +template <typename T> +struct DefineComparisonOps<MutableHandle<T>> : std::true_type { + static const T& get(const MutableHandle<T>& v) { return v.get(); } +}; + +} // namespace detail + +} /* namespace JS */ + +namespace js { + +namespace detail { + +// Default implementations for barrier methods on GC thing pointers. +template <typename T> +struct PtrBarrierMethodsBase { + static T* initial() { return nullptr; } + static gc::Cell* asGCThingOrNull(T* v) { + if (!v) { + return nullptr; + } + MOZ_ASSERT(uintptr_t(v) > 32); + return reinterpret_cast<gc::Cell*>(v); + } + static void exposeToJS(T* t) { + if (t) { + js::gc::ExposeGCThingToActiveJS(JS::GCCellPtr(t)); + } + } + static void readBarrier(T* t) { + if (t) { + js::gc::IncrementalReadBarrier(JS::GCCellPtr(t)); + } + } +}; + +} // namespace detail + +template <typename T> +struct BarrierMethods<T*> : public detail::PtrBarrierMethodsBase<T> { + static void postWriteBarrier(T** vp, T* prev, T* next) { + if (next) { + JS::AssertGCThingIsNotNurseryAllocable( + reinterpret_cast<js::gc::Cell*>(next)); + } + } +}; + +template <> +struct BarrierMethods<JSObject*> + : public detail::PtrBarrierMethodsBase<JSObject> { + static void postWriteBarrier(JSObject** vp, JSObject* prev, JSObject* next) { + JS::HeapObjectPostWriteBarrier(vp, prev, next); + } + static void exposeToJS(JSObject* obj) { + if (obj) { + JS::ExposeObjectToActiveJS(obj); + } + } +}; + +template <> +struct BarrierMethods<JSFunction*> + : public detail::PtrBarrierMethodsBase<JSFunction> { + static void postWriteBarrier(JSFunction** vp, JSFunction* prev, + JSFunction* next) { + JS::HeapObjectPostWriteBarrier(reinterpret_cast<JSObject**>(vp), + reinterpret_cast<JSObject*>(prev), + reinterpret_cast<JSObject*>(next)); + } + static void exposeToJS(JSFunction* fun) { + if (fun) { + JS::ExposeObjectToActiveJS(reinterpret_cast<JSObject*>(fun)); + } + } +}; + +template <> +struct BarrierMethods<JSString*> + : public detail::PtrBarrierMethodsBase<JSString> { + static void postWriteBarrier(JSString** vp, JSString* prev, JSString* next) { + JS::HeapStringPostWriteBarrier(vp, prev, next); + } +}; + +template <> +struct BarrierMethods<JS::BigInt*> + : public detail::PtrBarrierMethodsBase<JS::BigInt> { + static void postWriteBarrier(JS::BigInt** vp, JS::BigInt* prev, + JS::BigInt* next) { + JS::HeapBigIntPostWriteBarrier(vp, prev, next); + } +}; + +// Provide hash codes for Cell kinds that may be relocated and, thus, not have +// a stable address to use as the base for a hash code. Instead of the address, +// this hasher uses Cell::getUniqueId to provide exact matches and as a base +// for generating hash codes. +// +// Note: this hasher, like PointerHasher can "hash" a nullptr. While a nullptr +// would not likely be a useful key, there are some cases where being able to +// hash a nullptr is useful, either on purpose or because of bugs: +// (1) existence checks where the key may happen to be null and (2) some +// aggregate Lookup kinds embed a JSObject* that is frequently null and do not +// null test before dispatching to the hasher. +template <typename T> +struct JS_PUBLIC_API StableCellHasher { + using Key = T; + using Lookup = T; + + static bool maybeGetHash(const Lookup& l, mozilla::HashNumber* hashOut); + static bool ensureHash(const Lookup& l, HashNumber* hashOut); + static HashNumber hash(const Lookup& l); + static bool match(const Key& k, const Lookup& l); + // The rekey hash policy method is not provided since you dont't need to + // rekey any more when using this policy. +}; + +template <typename T> +struct JS_PUBLIC_API StableCellHasher<JS::Heap<T>> { + using Key = JS::Heap<T>; + using Lookup = T; + + static bool maybeGetHash(const Lookup& l, HashNumber* hashOut) { + return StableCellHasher<T>::maybeGetHash(l, hashOut); + } + static bool ensureHash(const Lookup& l, HashNumber* hashOut) { + return StableCellHasher<T>::ensureHash(l, hashOut); + } + static HashNumber hash(const Lookup& l) { + return StableCellHasher<T>::hash(l); + } + static bool match(const Key& k, const Lookup& l) { + return StableCellHasher<T>::match(k.unbarrieredGet(), l); + } +}; + +} // namespace js + +namespace mozilla { + +template <typename T> +struct FallibleHashMethods<js::StableCellHasher<T>> { + template <typename Lookup> + static bool maybeGetHash(Lookup&& l, HashNumber* hashOut) { + return js::StableCellHasher<T>::maybeGetHash(std::forward<Lookup>(l), + hashOut); + } + template <typename Lookup> + static bool ensureHash(Lookup&& l, HashNumber* hashOut) { + return js::StableCellHasher<T>::ensureHash(std::forward<Lookup>(l), + hashOut); + } +}; + +} // namespace mozilla + +namespace js { + +struct VirtualTraceable { + virtual ~VirtualTraceable() = default; + virtual void trace(JSTracer* trc, const char* name) = 0; +}; + +class StackRootedBase { + public: + StackRootedBase* previous() { return prev; } + + protected: + StackRootedBase** stack; + StackRootedBase* prev; + + template <typename T> + auto* derived() { + return static_cast<JS::Rooted<T>*>(this); + } +}; + +class PersistentRootedBase + : protected mozilla::LinkedListElement<PersistentRootedBase> { + protected: + friend class mozilla::LinkedList<PersistentRootedBase>; + friend class mozilla::LinkedListElement<PersistentRootedBase>; + + template <typename T> + auto* derived() { + return static_cast<JS::PersistentRooted<T>*>(this); + } +}; + +struct StackRootedTraceableBase : public StackRootedBase, + public VirtualTraceable {}; + +class PersistentRootedTraceableBase : public PersistentRootedBase, + public VirtualTraceable {}; + +template <typename Base, typename T> +class TypedRootedGCThingBase : public Base { + public: + void trace(JSTracer* trc, const char* name); +}; + +template <typename Base, typename T> +class TypedRootedTraceableBase : public Base { + public: + void trace(JSTracer* trc, const char* name) override { + auto* self = this->template derived<T>(); + JS::GCPolicy<T>::trace(trc, self->address(), name); + } +}; + +template <typename T> +struct RootedTraceableTraits { + using StackBase = TypedRootedTraceableBase<StackRootedTraceableBase, T>; + using PersistentBase = + TypedRootedTraceableBase<PersistentRootedTraceableBase, T>; +}; + +template <typename T> +struct RootedGCThingTraits { + using StackBase = TypedRootedGCThingBase<StackRootedBase, T>; + using PersistentBase = TypedRootedGCThingBase<PersistentRootedBase, T>; +}; + +} /* namespace js */ + +namespace JS { + +class JS_PUBLIC_API AutoGCRooter; + +enum class AutoGCRooterKind : uint8_t { + WrapperVector, /* js::AutoWrapperVector */ + Wrapper, /* js::AutoWrapperRooter */ + Custom, /* js::CustomAutoRooter */ + + Limit +}; + +using RootedListHeads = + mozilla::EnumeratedArray<RootKind, RootKind::Limit, js::StackRootedBase*>; + +using AutoRooterListHeads = + mozilla::EnumeratedArray<AutoGCRooterKind, AutoGCRooterKind::Limit, + AutoGCRooter*>; + +// Superclass of JSContext which can be used for rooting data in use by the +// current thread but that does not provide all the functions of a JSContext. +class RootingContext { + // Stack GC roots for Rooted GC heap pointers. + RootedListHeads stackRoots_; + template <typename T> + friend class Rooted; + + // Stack GC roots for AutoFooRooter classes. + AutoRooterListHeads autoGCRooters_; + friend class AutoGCRooter; + + // Gecko profiling metadata. + // This isn't really rooting related. It's only here because we want + // GetContextProfilingStackIfEnabled to be inlineable into non-JS code, and + // we didn't want to add another superclass of JSContext just for this. + js::GeckoProfilerThread geckoProfiler_; + + public: + explicit RootingContext(js::Nursery* nursery); + + void traceStackRoots(JSTracer* trc); + + /* Implemented in gc/RootMarking.cpp. */ + void traceAllGCRooters(JSTracer* trc); + void traceWrapperGCRooters(JSTracer* trc); + static void traceGCRooterList(JSTracer* trc, AutoGCRooter* head); + + void checkNoGCRooters(); + + js::GeckoProfilerThread& geckoProfiler() { return geckoProfiler_; } + + js::Nursery& nursery() const { + MOZ_ASSERT(nursery_); + return *nursery_; + } + + protected: + // The remaining members in this class should only be accessed through + // JSContext pointers. They are unrelated to rooting and are in place so + // that inlined API functions can directly access the data. + + /* The nursery. Null for non-main-thread contexts. */ + js::Nursery* nursery_; + + /* The current zone. */ + Zone* zone_; + + /* The current realm. */ + Realm* realm_; + + public: + /* Limit pointer for checking native stack consumption. */ + JS::NativeStackLimit nativeStackLimit[StackKindCount]; + +#ifdef __wasi__ + // For WASI we can't catch call-stack overflows with stack-pointer checks, so + // we count recursion depth with RAII based AutoCheckRecursionLimit. + uint32_t wasiRecursionDepth = 0u; + + static constexpr uint32_t wasiRecursionDepthLimit = 350u; +#endif // __wasi__ + + static const RootingContext* get(const JSContext* cx) { + return reinterpret_cast<const RootingContext*>(cx); + } + + static RootingContext* get(JSContext* cx) { + return reinterpret_cast<RootingContext*>(cx); + } + + friend JS::Realm* js::GetContextRealm(const JSContext* cx); + friend JS::Zone* js::GetContextZone(const JSContext* cx); +}; + +class JS_PUBLIC_API AutoGCRooter { + public: + using Kind = AutoGCRooterKind; + + AutoGCRooter(JSContext* cx, Kind kind) + : AutoGCRooter(JS::RootingContext::get(cx), kind) {} + AutoGCRooter(RootingContext* cx, Kind kind) + : down(cx->autoGCRooters_[kind]), + stackTop(&cx->autoGCRooters_[kind]), + kind_(kind) { + MOZ_ASSERT(this != *stackTop); + *stackTop = this; + } + + ~AutoGCRooter() { + MOZ_ASSERT(this == *stackTop); + *stackTop = down; + } + + void trace(JSTracer* trc); + + private: + friend class RootingContext; + + AutoGCRooter* const down; + AutoGCRooter** const stackTop; + + /* + * Discriminates actual subclass of this being used. The meaning is + * indicated by the corresponding value in the Kind enum. + */ + Kind kind_; + + /* No copy or assignment semantics. */ + AutoGCRooter(AutoGCRooter& ida) = delete; + void operator=(AutoGCRooter& ida) = delete; +} JS_HAZ_ROOTED_BASE; + +/** + * Custom rooting behavior for internal and external clients. + * + * Deprecated. Where possible, use Rooted<> instead. + */ +class MOZ_RAII JS_PUBLIC_API CustomAutoRooter : private AutoGCRooter { + public: + template <typename CX> + explicit CustomAutoRooter(const CX& cx) + : AutoGCRooter(cx, AutoGCRooter::Kind::Custom) {} + + friend void AutoGCRooter::trace(JSTracer* trc); + + protected: + virtual ~CustomAutoRooter() = default; + + /** Supplied by derived class to trace roots. */ + virtual void trace(JSTracer* trc) = 0; +}; + +namespace detail { + +template <typename T> +constexpr bool IsTraceable_v = + MapTypeToRootKind<T>::kind == JS::RootKind::Traceable; + +template <typename T> +using RootedTraits = + std::conditional_t<IsTraceable_v<T>, js::RootedTraceableTraits<T>, + js::RootedGCThingTraits<T>>; + +} /* namespace detail */ + +/** + * 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 RootedOperations<T> specialization containing them. + */ +template <typename T> +class MOZ_RAII Rooted : public detail::RootedTraits<T>::StackBase, + public js::RootedOperations<T, Rooted<T>> { + inline void registerWithRootLists(RootedListHeads& roots) { + this->stack = &roots[JS::MapTypeToRootKind<T>::kind]; + this->prev = *this->stack; + *this->stack = this; + } + + inline RootedListHeads& rootLists(RootingContext* cx) { + return cx->stackRoots_; + } + inline RootedListHeads& rootLists(JSContext* cx) { + return rootLists(RootingContext::get(cx)); + } + + public: + using ElementType = T; + + // Construct an empty Rooted holding a safely initialized but empty T. + // Requires T to have a copy constructor in order to copy the safely + // initialized value. + // + // Note that for SFINAE to reject this method, the 2nd template parameter must + // depend on RootingContext somehow even though we really only care about T. + template <typename RootingContext, + typename = std::enable_if_t<std::is_copy_constructible_v<T>, + RootingContext>> + explicit Rooted(const RootingContext& cx) + : ptr(SafelyInitialized<T>::create()) { + registerWithRootLists(rootLists(cx)); + } + + // Provide an initial value. Requires T to be constructible from the given + // argument. + template <typename RootingContext, typename S> + Rooted(const RootingContext& cx, S&& initial) + : ptr(std::forward<S>(initial)) { + MOZ_ASSERT(GCPolicy<T>::isValid(ptr)); + registerWithRootLists(rootLists(cx)); + } + + // (Traceables only) Construct the contained value from the given arguments. + // Constructs in-place, so T does not need to be copyable or movable. + // + // Note that a copyable Traceable passed only a RootingContext will + // choose the above SafelyInitialized<T> constructor, because otherwise + // identical functions with parameter packs are considered less specialized. + // + // The SFINAE type must again depend on an inferred template parameter. + template < + typename RootingContext, typename... CtorArgs, + typename = std::enable_if_t<detail::IsTraceable_v<T>, RootingContext>> + explicit Rooted(const RootingContext& cx, CtorArgs... args) + : ptr(std::forward<CtorArgs>(args)...) { + MOZ_ASSERT(GCPolicy<T>::isValid(ptr)); + registerWithRootLists(rootLists(cx)); + } + + ~Rooted() { + MOZ_ASSERT(*this->stack == this); + *this->stack = this->prev; + } + + /* + * This method is public for Rooted so that Codegen.py can use a Rooted + * interchangeably with a MutableHandleValue. + */ + void set(const T& value) { + ptr = value; + MOZ_ASSERT(GCPolicy<T>::isValid(ptr)); + } + void set(T&& value) { + ptr = std::move(value); + MOZ_ASSERT(GCPolicy<T>::isValid(ptr)); + } + + DECLARE_POINTER_CONSTREF_OPS(T); + DECLARE_POINTER_ASSIGN_OPS(Rooted, T); + + T& get() { return ptr; } + const T& get() const { return ptr; } + + T* address() { return &ptr; } + const T* address() const { return &ptr; } + + private: + T ptr; + + Rooted(const Rooted&) = delete; +} JS_HAZ_ROOTED; + +namespace detail { + +template <typename T> +struct DefineComparisonOps<Rooted<T>> : std::true_type { + static const T& get(const Rooted<T>& v) { return v.get(); } +}; + +} // namespace detail + +} /* namespace JS */ + +namespace js { + +/* + * Inlinable accessors for JSContext. + * + * - These must not be available on the more restricted superclasses of + * JSContext, so we can't simply define them on RootingContext. + * + * - They're perfectly ordinary JSContext functionality, so ought to be + * usable without resorting to jsfriendapi.h, and when JSContext is an + * incomplete type. + */ +inline JS::Realm* GetContextRealm(const JSContext* cx) { + return JS::RootingContext::get(cx)->realm_; +} + +inline JS::Compartment* GetContextCompartment(const JSContext* cx) { + if (JS::Realm* realm = GetContextRealm(cx)) { + return GetCompartmentForRealm(realm); + } + return nullptr; +} + +inline JS::Zone* GetContextZone(const JSContext* cx) { + return JS::RootingContext::get(cx)->zone_; +} + +inline ProfilingStack* GetContextProfilingStackIfEnabled(JSContext* cx) { + return JS::RootingContext::get(cx) + ->geckoProfiler() + .getProfilingStackIfEnabled(); +} + +/** + * Augment the generic Rooted<T> interface when T = JSObject* with + * class-querying and downcasting operations. + * + * Given a Rooted<JSObject*> obj, one can view + * Handle<StringObject*> h = obj.as<StringObject*>(); + * as an optimization of + * Rooted<StringObject*> rooted(cx, &obj->as<StringObject*>()); + * Handle<StringObject*> h = rooted; + */ +template <typename Container> +class RootedOperations<JSObject*, Container> + : public MutableWrappedPtrOperations<JSObject*, Container> { + public: + template <class U> + JS::Handle<U*> as() const; +}; + +/** + * Augment the generic Handle<T> interface when T = JSObject* with + * downcasting operations. + * + * Given a Handle<JSObject*> obj, one can view + * Handle<StringObject*> h = obj.as<StringObject*>(); + * as an optimization of + * Rooted<StringObject*> rooted(cx, &obj->as<StringObject*>()); + * Handle<StringObject*> h = rooted; + */ +template <typename Container> +class HandleOperations<JSObject*, Container> + : public WrappedPtrOperations<JSObject*, Container> { + public: + template <class U> + JS::Handle<U*> as() const; +}; + +} /* namespace js */ + +namespace JS { + +template <typename T> +template <typename S> +inline Handle<T>::Handle( + const Rooted<S>& root, + std::enable_if_t<std::is_convertible_v<S, T>, int> dummy) { + ptr = reinterpret_cast<const T*>(root.address()); +} + +template <typename T> +template <typename S> +inline Handle<T>::Handle( + const PersistentRooted<S>& root, + std::enable_if_t<std::is_convertible_v<S, T>, int> dummy) { + ptr = reinterpret_cast<const T*>(root.address()); +} + +template <typename T> +template <typename S> +inline Handle<T>::Handle( + MutableHandle<S>& root, + std::enable_if_t<std::is_convertible_v<S, T>, int> dummy) { + ptr = reinterpret_cast<const T*>(root.address()); +} + +template <typename T> +inline MutableHandle<T>::MutableHandle(Rooted<T>* root) { + static_assert(sizeof(MutableHandle<T>) == sizeof(T*), + "MutableHandle must be binary compatible with T*."); + ptr = root->address(); +} + +template <typename T> +inline MutableHandle<T>::MutableHandle(PersistentRooted<T>* root) { + static_assert(sizeof(MutableHandle<T>) == sizeof(T*), + "MutableHandle must be binary compatible with T*."); + ptr = root->address(); +} + +JS_PUBLIC_API void AddPersistentRoot(RootingContext* cx, RootKind kind, + js::PersistentRootedBase* root); + +JS_PUBLIC_API void AddPersistentRoot(JSRuntime* rt, RootKind kind, + js::PersistentRootedBase* root); + +/** + * A copyable, assignable global GC root type with arbitrary lifetime, an + * infallible constructor, and automatic unrooting on destruction. + * + * These roots can be used in heap-allocated data structures, so they are not + * associated with any particular JSContext or stack. They are registered with + * the JSRuntime itself, without locking. Initialization may take place on + * construction, or in two phases if the no-argument constructor is called + * followed by init(). + * + * Note that you must not use an PersistentRooted in an object owned by a JS + * object: + * + * Whenever one object whose lifetime is decided by the GC refers to another + * such object, that edge must be traced only if the owning JS object is traced. + * This applies not only to JS objects (which obviously are managed by the GC) + * but also to C++ objects owned by JS objects. + * + * If you put a PersistentRooted in such a C++ object, that is almost certainly + * a leak. When a GC begins, the referent of the PersistentRooted is treated as + * live, unconditionally (because a PersistentRooted is a *root*), even if the + * JS object that owns it is unreachable. If there is any path from that + * referent back to the JS object, then the C++ object containing the + * PersistentRooted will not be destructed, and the whole blob of objects will + * not be freed, even if there are no references to them from the outside. + * + * In the context of Firefox, this is a severe restriction: almost everything in + * Firefox is owned by some JS object or another, so using PersistentRooted in + * such objects would introduce leaks. For these kinds of edges, Heap<T> or + * TenuredHeap<T> would be better types. It's up to the implementor of the type + * containing Heap<T> or TenuredHeap<T> members to make sure their referents get + * marked when the object itself is marked. + */ +template <typename T> +class PersistentRooted : public detail::RootedTraits<T>::PersistentBase, + public js::RootedOperations<T, PersistentRooted<T>> { + void registerWithRootLists(RootingContext* cx) { + MOZ_ASSERT(!initialized()); + JS::RootKind kind = JS::MapTypeToRootKind<T>::kind; + AddPersistentRoot(cx, kind, this); + } + + void registerWithRootLists(JSRuntime* rt) { + MOZ_ASSERT(!initialized()); + JS::RootKind kind = JS::MapTypeToRootKind<T>::kind; + AddPersistentRoot(rt, kind, this); + } + + // Used when JSContext type is incomplete and so it is not known to inherit + // from RootingContext. + void registerWithRootLists(JSContext* cx) { + registerWithRootLists(RootingContext::get(cx)); + } + + public: + using ElementType = T; + + PersistentRooted() : ptr(SafelyInitialized<T>::create()) {} + + template < + typename RootHolder, + typename = std::enable_if_t<std::is_copy_constructible_v<T>, RootHolder>> + explicit PersistentRooted(const RootHolder& cx) + : ptr(SafelyInitialized<T>::create()) { + registerWithRootLists(cx); + } + + template < + typename RootHolder, typename U, + typename = std::enable_if_t<std::is_constructible_v<T, U>, RootHolder>> + PersistentRooted(const RootHolder& cx, U&& initial) + : ptr(std::forward<U>(initial)) { + registerWithRootLists(cx); + } + + template <typename RootHolder, typename... CtorArgs, + typename = std::enable_if_t<detail::IsTraceable_v<T>, RootHolder>> + explicit PersistentRooted(const RootHolder& cx, CtorArgs... args) + : ptr(std::forward<CtorArgs>(args)...) { + registerWithRootLists(cx); + } + + PersistentRooted(const PersistentRooted& rhs) : ptr(rhs.ptr) { + /* + * Copy construction takes advantage of the fact that the original + * is already inserted, and simply adds itself to whatever list the + * original was on - no JSRuntime pointer needed. + * + * This requires mutating rhs's links, but those should be 'mutable' + * anyway. C++ doesn't let us declare mutable base classes. + */ + const_cast<PersistentRooted&>(rhs).setNext(this); + } + + bool initialized() const { return this->isInList(); } + + void init(RootingContext* cx) { init(cx, SafelyInitialized<T>::create()); } + void init(JSContext* cx) { init(RootingContext::get(cx)); } + + template <typename U> + void init(RootingContext* cx, U&& initial) { + ptr = std::forward<U>(initial); + registerWithRootLists(cx); + } + template <typename U> + void init(JSContext* cx, U&& initial) { + ptr = std::forward<U>(initial); + registerWithRootLists(RootingContext::get(cx)); + } + + void reset() { + if (initialized()) { + set(SafelyInitialized<T>::create()); + this->remove(); + } + } + + DECLARE_POINTER_CONSTREF_OPS(T); + DECLARE_POINTER_ASSIGN_OPS(PersistentRooted, T); + + T& get() { return ptr; } + const T& get() const { return ptr; } + + T* address() { + MOZ_ASSERT(initialized()); + return &ptr; + } + const T* address() const { return &ptr; } + + template <typename U> + void set(U&& value) { + MOZ_ASSERT(initialized()); + ptr = std::forward<U>(value); + } + + private: + T ptr; +} JS_HAZ_ROOTED; + +namespace detail { + +template <typename T> +struct DefineComparisonOps<PersistentRooted<T>> : std::true_type { + static const T& get(const PersistentRooted<T>& v) { return v.get(); } +}; + +} // namespace detail + +} /* namespace JS */ + +namespace js { + +template <typename T, typename D, typename Container> +class WrappedPtrOperations<UniquePtr<T, D>, Container> { + const UniquePtr<T, D>& uniquePtr() const { + return static_cast<const Container*>(this)->get(); + } + + public: + explicit operator bool() const { return !!uniquePtr(); } + T* get() const { return uniquePtr().get(); } + T* operator->() const { return get(); } + T& operator*() const { return *uniquePtr(); } +}; + +template <typename T, typename D, typename Container> +class MutableWrappedPtrOperations<UniquePtr<T, D>, Container> + : public WrappedPtrOperations<UniquePtr<T, D>, Container> { + UniquePtr<T, D>& uniquePtr() { return static_cast<Container*>(this)->get(); } + + public: + [[nodiscard]] typename UniquePtr<T, D>::Pointer release() { + return uniquePtr().release(); + } + void reset(T* ptr = T()) { uniquePtr().reset(ptr); } +}; + +template <typename T, typename Container> +class WrappedPtrOperations<mozilla::Maybe<T>, Container> { + const mozilla::Maybe<T>& maybe() const { + return static_cast<const Container*>(this)->get(); + } + + public: + // This only supports a subset of Maybe's interface. + bool isSome() const { return maybe().isSome(); } + bool isNothing() const { return maybe().isNothing(); } + const T value() const { return maybe().value(); } + const T* operator->() const { return maybe().ptr(); } + const T& operator*() const { return maybe().ref(); } +}; + +template <typename T, typename Container> +class MutableWrappedPtrOperations<mozilla::Maybe<T>, Container> + : public WrappedPtrOperations<mozilla::Maybe<T>, Container> { + mozilla::Maybe<T>& maybe() { return static_cast<Container*>(this)->get(); } + + public: + // This only supports a subset of Maybe's interface. + T* operator->() { return maybe().ptr(); } + T& operator*() { return maybe().ref(); } + void reset() { return maybe().reset(); } +}; + +namespace gc { + +template <typename T, typename TraceCallbacks> +void CallTraceCallbackOnNonHeap(T* v, const TraceCallbacks& aCallbacks, + const char* aName, void* aClosure) { + static_assert(sizeof(T) == sizeof(JS::Heap<T>), + "T and Heap<T> must be compatible."); + MOZ_ASSERT(v); + mozilla::DebugOnly<Cell*> cell = BarrierMethods<T>::asGCThingOrNull(*v); + MOZ_ASSERT(cell); + MOZ_ASSERT(!IsInsideNursery(cell)); + JS::Heap<T>* asHeapT = reinterpret_cast<JS::Heap<T>*>(v); + aCallbacks.Trace(asHeapT, aName, aClosure); +} + +} /* namespace gc */ + +template <typename Wrapper, typename T1, typename T2> +class WrappedPtrOperations<std::pair<T1, T2>, Wrapper> { + const std::pair<T1, T2>& pair() const { + return static_cast<const Wrapper*>(this)->get(); + } + + public: + const T1& first() const { return pair().first; } + const T2& second() const { return pair().second; } +}; + +template <typename Wrapper, typename T1, typename T2> +class MutableWrappedPtrOperations<std::pair<T1, T2>, Wrapper> + : public WrappedPtrOperations<std::pair<T1, T2>, Wrapper> { + std::pair<T1, T2>& pair() { return static_cast<Wrapper*>(this)->get(); } + + public: + T1& first() { return pair().first; } + T2& second() { return pair().second; } +}; + +} /* namespace js */ + +#endif /* js_RootingAPI_h */ |