1 // Copyright 2011 the V8 project authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef V8_HANDLES_MAYBE_HANDLES_H_ 6 #define V8_HANDLES_MAYBE_HANDLES_H_ 7 8 #include <type_traits> 9 10 #include "src/handles/handles.h" 11 12 namespace v8 { 13 namespace internal { 14 15 struct NullMaybeHandleType {}; 16 17 constexpr NullMaybeHandleType kNullMaybeHandle; 18 19 // ---------------------------------------------------------------------------- 20 // A Handle can be converted into a MaybeHandle. Converting a MaybeHandle 21 // into a Handle requires checking that it does not point to nullptr. This 22 // ensures nullptr checks before use. 23 // 24 // Also note that Handles do not provide default equality comparison or hashing 25 // operators on purpose. Such operators would be misleading, because intended 26 // semantics is ambiguous between Handle location and object identity. 27 template <typename T> 28 class MaybeHandle final { 29 public: 30 V8_INLINE MaybeHandle() = default; 31 MaybeHandle(NullMaybeHandleType)32 V8_INLINE MaybeHandle(NullMaybeHandleType) {} 33 34 // Constructor for handling automatic up casting from Handle. 35 // Ex. Handle<JSArray> can be passed when MaybeHandle<Object> is expected. 36 template <typename S, typename = typename std::enable_if< 37 std::is_convertible<S*, T*>::value>::type> MaybeHandle(Handle<S> handle)38 V8_INLINE MaybeHandle(Handle<S> handle) : location_(handle.location_) {} 39 40 // Constructor for handling automatic up casting. 41 // Ex. MaybeHandle<JSArray> can be passed when Handle<Object> is expected. 42 template <typename S, typename = typename std::enable_if< 43 std::is_convertible<S*, T*>::value>::type> MaybeHandle(MaybeHandle<S> maybe_handle)44 V8_INLINE MaybeHandle(MaybeHandle<S> maybe_handle) 45 : location_(maybe_handle.location_) {} 46 47 V8_INLINE MaybeHandle(T object, Isolate* isolate); 48 V8_INLINE MaybeHandle(T object, LocalHeap* local_heap); 49 Assert()50 V8_INLINE void Assert() const { DCHECK_NOT_NULL(location_); } Check()51 V8_INLINE void Check() const { CHECK_NOT_NULL(location_); } 52 ToHandleChecked()53 V8_INLINE Handle<T> ToHandleChecked() const { 54 Check(); 55 return Handle<T>(location_); 56 } 57 58 // Convert to a Handle with a type that can be upcasted to. 59 template <typename S> ToHandle(Handle<S> * out)60 V8_WARN_UNUSED_RESULT V8_INLINE bool ToHandle(Handle<S>* out) const { 61 if (location_ == nullptr) { 62 *out = Handle<T>::null(); 63 return false; 64 } else { 65 *out = Handle<T>(location_); 66 return true; 67 } 68 } 69 70 // Returns the raw address where this handle is stored. This should only be 71 // used for hashing handles; do not ever try to dereference it. address()72 V8_INLINE Address address() const { 73 return reinterpret_cast<Address>(location_); 74 } 75 is_null()76 bool is_null() const { return location_ == nullptr; } 77 78 protected: 79 Address* location_ = nullptr; 80 81 // MaybeHandles of different classes are allowed to access each 82 // other's location_. 83 template <typename> 84 friend class MaybeHandle; 85 }; 86 87 // A handle which contains a potentially weak pointer. Keeps it alive (strongly) 88 // while the MaybeObjectHandle is alive. 89 class MaybeObjectHandle { 90 public: MaybeObjectHandle()91 inline MaybeObjectHandle() 92 : reference_type_(HeapObjectReferenceType::STRONG) {} 93 inline MaybeObjectHandle(MaybeObject object, Isolate* isolate); 94 inline MaybeObjectHandle(Object object, Isolate* isolate); 95 inline MaybeObjectHandle(MaybeObject object, LocalHeap* local_heap); 96 inline MaybeObjectHandle(Object object, LocalHeap* local_heap); 97 inline explicit MaybeObjectHandle(Handle<Object> object); 98 99 static inline MaybeObjectHandle Weak(Object object, Isolate* isolate); 100 static inline MaybeObjectHandle Weak(Handle<Object> object); 101 102 inline MaybeObject operator*() const; 103 inline MaybeObject operator->() const; 104 inline Handle<Object> object() const; 105 106 inline bool is_identical_to(const MaybeObjectHandle& other) const; is_null()107 bool is_null() const { return handle_.is_null(); } 108 109 private: 110 inline MaybeObjectHandle(Object object, 111 HeapObjectReferenceType reference_type, 112 Isolate* isolate); 113 inline MaybeObjectHandle(Handle<Object> object, 114 HeapObjectReferenceType reference_type); 115 116 HeapObjectReferenceType reference_type_; 117 MaybeHandle<Object> handle_; 118 }; 119 120 } // namespace internal 121 } // namespace v8 122 123 #endif // V8_HANDLES_MAYBE_HANDLES_H_ 124