Line data    Source code

       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_MAYBE_HANDLES_H_
       6             : #define V8_MAYBE_HANDLES_H_
       7             : 
       8             : #include <type_traits>
       9             : 
      10             : #include "src/handles.h"
      11             : 
      12             : namespace v8 {
      13             : namespace internal {
      14             : 
      15             : // ----------------------------------------------------------------------------
      16             : // A Handle can be converted into a MaybeHandle. Converting a MaybeHandle
      17             : // into a Handle requires checking that it does not point to nullptr.  This
      18             : // ensures nullptr checks before use.
      19             : //
      20             : // Also note that Handles do not provide default equality comparison or hashing
      21             : // operators on purpose. Such operators would be misleading, because intended
      22             : // semantics is ambiguous between Handle location and object identity.
      23             : template <typename T>
      24             : class MaybeHandle final {
      25             :  public:
      26    14378963 :   V8_INLINE MaybeHandle() = default;
      27             : 
      28             :   // Constructor for handling automatic up casting from Handle.
      29             :   // Ex. Handle<JSArray> can be passed when MaybeHandle<Object> is expected.
      30             :   template <typename S, typename = typename std::enable_if<
      31             :                             std::is_convertible<S*, T*>::value>::type>
      32    65799141 :   V8_INLINE MaybeHandle(Handle<S> handle) : location_(handle.location_) {}
      33             : 
      34             :   // Constructor for handling automatic up casting.
      35             :   // Ex. MaybeHandle<JSArray> can be passed when Handle<Object> is expected.
      36             :   template <typename S, typename = typename std::enable_if<
      37             :                             std::is_convertible<S*, T*>::value>::type>
      38             :   V8_INLINE MaybeHandle(MaybeHandle<S> maybe_handle)
      39     5915144 :       : location_(maybe_handle.location_) {}
      40             : 
      41             :   V8_INLINE MaybeHandle(T object, Isolate* isolate);
      42             : 
      43             :   V8_INLINE void Assert() const { DCHECK_NOT_NULL(location_); }
      44   279922670 :   V8_INLINE void Check() const { CHECK_NOT_NULL(location_); }
      45             : 
      46             :   V8_INLINE Handle<T> ToHandleChecked() const {
      47             :     Check();
      48             :     return Handle<T>(location_);
      49             :   }
      50             : 
      51             :   // Convert to a Handle with a type that can be upcasted to.
      52             :   template <typename S>
      53             :   V8_INLINE bool ToHandle(Handle<S>* out) const {
      54   407657187 :     if (location_ == nullptr) {
      55    10579004 :       *out = Handle<T>::null();
      56             :       return false;
      57             :     } else {
      58    32151803 :       *out = Handle<T>(location_);
      59             :       return true;
      60             :     }
      61             :   }
      62             : 
      63             :   // Returns the raw address where this handle is stored. This should only be
      64             :   // used for hashing handles; do not ever try to dereference it.
      65             :   V8_INLINE Address address() const {
      66     1009742 :     return reinterpret_cast<Address>(location_);
      67             :   }
      68             : 
      69    68742015 :   bool is_null() const { return location_ == nullptr; }
      70             : 
      71             :  protected:
      72             :   Address* location_ = nullptr;
      73             : 
      74             :   // MaybeHandles of different classes are allowed to access each
      75             :   // other's location_.
      76             :   template <typename>
      77             :   friend class MaybeHandle;
      78             : };
      79             : 
      80             : // A handle which contains a potentially weak pointer. Keeps it alive (strongly)
      81             : // while the MaybeObjectHandle is alive.
      82             : class MaybeObjectHandle {
      83             :  public:
      84             :   inline MaybeObjectHandle();
      85             :   inline MaybeObjectHandle(MaybeObject object, Isolate* isolate);
      86             :   inline MaybeObjectHandle(Object object, Isolate* isolate);
      87             :   inline explicit MaybeObjectHandle(Handle<Object> object);
      88             : 
      89             :   static inline MaybeObjectHandle Weak(Object object, Isolate* isolate);
      90             :   static inline MaybeObjectHandle Weak(Handle<Object> object);
      91             : 
      92             :   inline MaybeObject operator*() const;
      93             :   inline MaybeObject operator->() const;
      94             :   inline Handle<Object> object() const;
      95             : 
      96       12996 :   bool is_identical_to(const MaybeObjectHandle& other) const {
      97             :     Handle<Object> this_handle;
      98             :     Handle<Object> other_handle;
      99       17663 :     return reference_type_ == other.reference_type_ &&
     100             :            handle_.ToHandle(&this_handle) ==
     101       17663 :                other.handle_.ToHandle(&other_handle) &&
     102       12996 :            this_handle.is_identical_to(other_handle);
     103             :   }
     104             : 
     105             :   bool is_null() const { return handle_.is_null(); }
     106             : 
     107             :  private:
     108             :   inline MaybeObjectHandle(Object object,
     109             :                            HeapObjectReferenceType reference_type,
     110             :                            Isolate* isolate);
     111             :   inline MaybeObjectHandle(Handle<Object> object,
     112             :                            HeapObjectReferenceType reference_type);
     113             : 
     114             :   HeapObjectReferenceType reference_type_;
     115             :   MaybeHandle<Object> handle_;
     116             : };
     117             : 
     118             : }  // namespace internal
     119             : }  // namespace v8
     120             : 
     121             : #endif  // V8_MAYBE_HANDLES_H_