diff options
Diffstat (limited to 'node_modules/nan/doc/persistent.md')
| -rw-r--r-- | node_modules/nan/doc/persistent.md | 296 |
1 files changed, 0 insertions, 296 deletions
diff --git a/node_modules/nan/doc/persistent.md b/node_modules/nan/doc/persistent.md deleted file mode 100644 index 2e13f6b..0000000 --- a/node_modules/nan/doc/persistent.md +++ /dev/null @@ -1,296 +0,0 @@ -## Persistent references - -An object reference that is independent of any `HandleScope` is a _persistent_ reference. Where a `Local` handle only lives as long as the `HandleScope` in which it was allocated, a `Persistent` handle remains valid until it is explicitly disposed. - -Due to the evolution of the V8 API, it is necessary for NAN to provide a wrapper implementation of the `Persistent` classes to supply compatibility across the V8 versions supported. - - - <a href="#api_nan_persistent_base"><b><code>Nan::PersistentBase & v8::PersistentBase</code></b></a> - - <a href="#api_nan_non_copyable_persistent_traits"><b><code>Nan::NonCopyablePersistentTraits & v8::NonCopyablePersistentTraits</code></b></a> - - <a href="#api_nan_copyable_persistent_traits"><b><code>Nan::CopyablePersistentTraits & v8::CopyablePersistentTraits</code></b></a> - - <a href="#api_nan_persistent"><b><code>Nan::Persistent</code></b></a> - - <a href="#api_nan_global"><b><code>Nan::Global</code></b></a> - - <a href="#api_nan_weak_callback_info"><b><code>Nan::WeakCallbackInfo</code></b></a> - - <a href="#api_nan_weak_callback_type"><b><code>Nan::WeakCallbackType</code></b></a> - -Also see the V8 Embedders Guide section on [Handles and Garbage Collection](https://developers.google.com/v8/embed#handles). - -<a name="api_nan_persistent_base"></a> -### Nan::PersistentBase & v8::PersistentBase - -A persistent handle contains a reference to a storage cell in V8 which holds an object value and which is updated by the garbage collector whenever the object is moved. A new storage cell can be created using the constructor or `Nan::PersistentBase::Reset()`. Existing handles can be disposed using an argument-less `Nan::PersistentBase::Reset()`. - -Definition: - -_(note: this is implemented as `Nan::PersistentBase` for older versions of V8 and the native `v8::PersistentBase` is used for newer versions of V8)_ - -```c++ -template<typename T> class PersistentBase { - public: - /** - * If non-empty, destroy the underlying storage cell - */ - void Reset(); - - /** - * If non-empty, destroy the underlying storage cell and create a new one with - * the contents of another if it is also non-empty - */ - template<typename S> void Reset(const v8::Local<S> &other); - - /** - * If non-empty, destroy the underlying storage cell and create a new one with - * the contents of another if it is also non-empty - */ - template<typename S> void Reset(const PersistentBase<S> &other); - - /** Returns true if the handle is empty. */ - bool IsEmpty() const; - - /** - * If non-empty, destroy the underlying storage cell - * IsEmpty() will return true after this call. - */ - void Empty(); - - template<typename S> bool operator==(const PersistentBase<S> &that); - - template<typename S> bool operator==(const v8::Local<S> &that); - - template<typename S> bool operator!=(const PersistentBase<S> &that); - - template<typename S> bool operator!=(const v8::Local<S> &that); - - /** - * Install a finalization callback on this object. - * NOTE: There is no guarantee as to *when* or even *if* the callback is - * invoked. The invocation is performed solely on a best effort basis. - * As always, GC-based finalization should *not* be relied upon for any - * critical form of resource management! At the moment you can either - * specify a parameter for the callback or the location of two internal - * fields in the dying object. - */ - template<typename P> - void SetWeak(P *parameter, - typename WeakCallbackInfo<P>::Callback callback, - WeakCallbackType type); - - void ClearWeak(); - - /** - * Marks the reference to this object independent. Garbage collector is free - * to ignore any object groups containing this object. Weak callback for an - * independent handle should not assume that it will be preceded by a global - * GC prologue callback or followed by a global GC epilogue callback. - */ - void MarkIndependent() const; - - bool IsIndependent() const; - - /** Checks if the handle holds the only reference to an object. */ - bool IsNearDeath() const; - - /** Returns true if the handle's reference is weak. */ - bool IsWeak() const -}; -``` - -See the V8 documentation for [`PersistentBase`](https://v8docs.nodesource.com/node-8.16/d4/dca/classv8_1_1_persistent_base.html) for further information. - -**Tip:** To get a `v8::Local` reference to the original object back from a `PersistentBase` or `Persistent` object: - -```c++ -v8::Local<v8::Object> object = Nan::New(persistent); -``` - -<a name="api_nan_non_copyable_persistent_traits"></a> -### Nan::NonCopyablePersistentTraits & v8::NonCopyablePersistentTraits - -Default traits for `Nan::Persistent`. This class does not allow use of the a copy constructor or assignment operator. At present `kResetInDestructor` is not set, but that will change in a future version. - -Definition: - -_(note: this is implemented as `Nan::NonCopyablePersistentTraits` for older versions of V8 and the native `v8::NonCopyablePersistentTraits` is used for newer versions of V8)_ - -```c++ -template<typename T> class NonCopyablePersistentTraits { - public: - typedef Persistent<T, NonCopyablePersistentTraits<T> > NonCopyablePersistent; - - static const bool kResetInDestructor = false; - - template<typename S, typename M> - static void Copy(const Persistent<S, M> &source, - NonCopyablePersistent *dest); - - template<typename O> static void Uncompilable(); -}; -``` - -See the V8 documentation for [`NonCopyablePersistentTraits`](https://v8docs.nodesource.com/node-8.16/de/d73/classv8_1_1_non_copyable_persistent_traits.html) for further information. - -<a name="api_nan_copyable_persistent_traits"></a> -### Nan::CopyablePersistentTraits & v8::CopyablePersistentTraits - -A helper class of traits to allow copying and assignment of `Persistent`. This will clone the contents of storage cell, but not any of the flags, etc.. - -Definition: - -_(note: this is implemented as `Nan::CopyablePersistentTraits` for older versions of V8 and the native `v8::NonCopyablePersistentTraits` is used for newer versions of V8)_ - -```c++ -template<typename T> -class CopyablePersistentTraits { - public: - typedef Persistent<T, CopyablePersistentTraits<T> > CopyablePersistent; - - static const bool kResetInDestructor = true; - - template<typename S, typename M> - static void Copy(const Persistent<S, M> &source, - CopyablePersistent *dest); -}; -``` - -See the V8 documentation for [`CopyablePersistentTraits`](https://v8docs.nodesource.com/node-8.16/da/d5c/structv8_1_1_copyable_persistent_traits.html) for further information. - -<a name="api_nan_persistent"></a> -### Nan::Persistent - -A type of `PersistentBase` which allows copy and assignment. Copy, assignment and destructor behavior is controlled by the traits class `M`. - -Definition: - -```c++ -template<typename T, typename M = NonCopyablePersistentTraits<T> > -class Persistent; - -template<typename T, typename M> class Persistent : public PersistentBase<T> { - public: - /** - * A Persistent with no storage cell. - */ - Persistent(); - - /** - * Construct a Persistent from a v8::Local. When the v8::Local is non-empty, a - * new storage cell is created pointing to the same object, and no flags are - * set. - */ - template<typename S> Persistent(v8::Local<S> that); - - /** - * Construct a Persistent from a Persistent. When the Persistent is non-empty, - * a new storage cell is created pointing to the same object, and no flags are - * set. - */ - Persistent(const Persistent &that); - - /** - * The copy constructors and assignment operator create a Persistent exactly - * as the Persistent constructor, but the Copy function from the traits class - * is called, allowing the setting of flags based on the copied Persistent. - */ - Persistent &operator=(const Persistent &that); - - template <typename S, typename M2> - Persistent &operator=(const Persistent<S, M2> &that); - - /** - * The destructor will dispose the Persistent based on the kResetInDestructor - * flags in the traits class. Since not calling dispose can result in a - * memory leak, it is recommended to always set this flag. - */ - ~Persistent(); -}; -``` - -See the V8 documentation for [`Persistent`](https://v8docs.nodesource.com/node-8.16/d2/d78/classv8_1_1_persistent.html) for further information. - -<a name="api_nan_global"></a> -### Nan::Global - -A type of `PersistentBase` which has move semantics. - -```c++ -template<typename T> class Global : public PersistentBase<T> { - public: - /** - * A Global with no storage cell. - */ - Global(); - - /** - * Construct a Global from a v8::Local. When the v8::Local is non-empty, a new - * storage cell is created pointing to the same object, and no flags are set. - */ - template<typename S> Global(v8::Local<S> that); - /** - * Construct a Global from a PersistentBase. When the Persistent is non-empty, - * a new storage cell is created pointing to the same object, and no flags are - * set. - */ - template<typename S> Global(const PersistentBase<S> &that); - - /** - * Pass allows returning globals from functions, etc. - */ - Global Pass(); -}; -``` - -See the V8 documentation for [`Global`](https://v8docs.nodesource.com/node-8.16/d5/d40/classv8_1_1_global.html) for further information. - -<a name="api_nan_weak_callback_info"></a> -### Nan::WeakCallbackInfo - -`Nan::WeakCallbackInfo` is used as an argument when setting a persistent reference as weak. You may need to free any external resources attached to the object. It is a mirror of `v8:WeakCallbackInfo` as found in newer versions of V8. - -Definition: - -```c++ -template<typename T> class WeakCallbackInfo { - public: - typedef void (*Callback)(const WeakCallbackInfo<T>& data); - - v8::Isolate *GetIsolate() const; - - /** - * Get the parameter that was associated with the weak handle. - */ - T *GetParameter() const; - - /** - * Get pointer from internal field, index can be 0 or 1. - */ - void *GetInternalField(int index) const; -}; -``` - -Example usage: - -```c++ -void weakCallback(const WeakCallbackInfo<int> &data) { - int *parameter = data.GetParameter(); - delete parameter; -} - -Persistent<v8::Object> obj; -int *data = new int(0); -obj.SetWeak(data, callback, WeakCallbackType::kParameter); -``` - -See the V8 documentation for [`WeakCallbackInfo`](https://v8docs.nodesource.com/node-8.16/d8/d06/classv8_1_1_weak_callback_info.html) for further information. - -<a name="api_nan_weak_callback_type"></a> -### Nan::WeakCallbackType - -Represents the type of a weak callback. -A weak callback of type `kParameter` makes the supplied parameter to `Nan::PersistentBase::SetWeak` available through `WeakCallbackInfo::GetParameter`. -A weak callback of type `kInternalFields` uses up to two internal fields at indices 0 and 1 on the `Nan::PersistentBase<v8::Object>` being made weak. -Note that only `v8::Object`s and derivatives can have internal fields. - -Definition: - -```c++ -enum class WeakCallbackType { kParameter, kInternalFields }; -``` |