v8/src/handles.h

// Copyright 2006-2008 the V8 project authors. All rights reserved.
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#ifndef V8_HANDLES_H_
#define V8_HANDLES_H_

#include "apiutils.h"

namespace v8 {
namespace internal {

// ----------------------------------------------------------------------------
// A Handle provides a reference to an object that survives relocation by
// the garbage collector.
// Handles are only valid within a HandleScope.
// When a handle is created for an object a cell is allocated in the heap.

template<class T>
class Handle {
 public:
  INLINE(explicit Handle(T** location)) { location_ = location; }
  INLINE(explicit Handle(T* obj));

  INLINE(Handle()) : location_(NULL) {}

  // Constructor for handling automatic up casting.
  // Ex. Handle<JSFunction> can be passed when Handle<Object> is expected.
  template <class S> Handle(Handle<S> handle) {
#ifdef DEBUG
    T* a = NULL;
    S* b = NULL;
    a = b;  // Fake assignment to enforce type checks.
    USE(a);
#endif
    location_ = reinterpret_cast<T**>(handle.location());
  }

  INLINE(T* operator ->() const) { return operator*(); }

  // Check if this handle refers to the exact same object as the other handle.
  bool is_identical_to(const Handle<T> other) const {
    return operator*() == *other;
  }

  // Provides the C++ dereference operator.
  INLINE(T* operator*() const);

  // Returns the address to where the raw pointer is stored.
  T** location() const {
    ASSERT(location_ == NULL ||
           reinterpret_cast<Address>(*location_) != kZapValue);
    return location_;
  }

  template <class S> static Handle<T> cast(Handle<S> that) {
    T::cast(*that);
    return Handle<T>(reinterpret_cast<T**>(that.location()));
  }

  static Handle<T> null() { return Handle<T>(); }
  bool is_null() { return location_ == NULL; }

  // Closes the given scope, but lets this handle escape. See
  // implementation in api.h.
  inline Handle<T> EscapeFrom(v8::HandleScope* scope);

 private:
  T** location_;
};


// A stack-allocated class that governs a number of local handles.
// After a handle scope has been created, all local handles will be
// allocated within that handle scope until either the handle scope is
// deleted or another handle scope is created.  If there is already a
// handle scope and a new one is created, all allocations will take
// place in the new handle scope until it is deleted.  After that,
// new handles will again be allocated in the original handle scope.
//
// After the handle scope of a local handle has been deleted the
// garbage collector will no longer track the object stored in the
// handle and may deallocate it.  The behavior of accessing a handle
// for which the handle scope has been deleted is undefined.
class HandleScope {
 public:
  HandleScope() : previous_(current_) {
    current_.extensions = 0;
  }

  ~HandleScope() {
    Leave(&previous_);
  }

  // Counts the number of allocated handles.
  static int NumberOfHandles();

  // Creates a new handle with the given value.
  template <typename T>
  static inline T** CreateHandle(T* value) {
    internal::Object** cur = current_.next;
    if (cur == current_.limit) cur = Extend();
    // Update the current next field, set the value in the created
    // handle, and return the result.
    ASSERT(cur < current_.limit);
    current_.next = cur + 1;

    T** result = reinterpret_cast<T**>(cur);
    *result = value;
    return result;
  }

  // Deallocates any extensions used by the current scope.
  static void DeleteExtensions();

  static Address current_extensions_address();
  static Address current_next_address();
  static Address current_limit_address();

 private:
  // Prevent heap allocation or illegal handle scopes.
  HandleScope(const HandleScope&);
  void operator=(const HandleScope&);
  void* operator new(size_t size);
  void operator delete(void* size_t);

  static v8::ImplementationUtilities::HandleScopeData current_;
  const v8::ImplementationUtilities::HandleScopeData previous_;

  // Pushes a fresh handle scope to be used when allocating new handles.
  static void Enter(
      v8::ImplementationUtilities::HandleScopeData* previous) {
    *previous = current_;
    current_.extensions = 0;
  }

  // Re-establishes the previous scope state. Should be called only
  // once, and only for the current scope.
  static void Leave(
      const v8::ImplementationUtilities::HandleScopeData* previous) {
    if (current_.extensions > 0) {
      DeleteExtensions();
    }
    current_ = *previous;
#ifdef DEBUG
    ZapRange(current_.next, current_.limit);
#endif
  }

  // Extend the handle scope making room for more handles.
  static internal::Object** Extend();

  // Zaps the handles in the half-open interval [start, end).
  static void ZapRange(internal::Object** start, internal::Object** end);

  friend class v8::HandleScope;
  friend class v8::ImplementationUtilities;
};


// ----------------------------------------------------------------------------
// Handle operations.
// They might invoke garbage collection. The result is an handle to
// an object of expected type, or the handle is an error if running out
// of space or encountering an internal error.

void NormalizeProperties(Handle<JSObject> object,
                         PropertyNormalizationMode mode,
                         int expected_additional_properties);
void NormalizeElements(Handle<JSObject> object);
void TransformToFastProperties(Handle<JSObject> object,
                               int unused_property_fields);

// Flattens a string.
void FlattenString(Handle<String> str);

// Flattens a string and returns the underlying external or sequential
// string.
Handle<String> FlattenGetString(Handle<String> str);

Handle<Object> SetProperty(Handle<JSObject> object,
                           Handle<String> key,
                           Handle<Object> value,
                           PropertyAttributes attributes);

Handle<Object> SetProperty(Handle<Object> object,
                           Handle<Object> key,
                           Handle<Object> value,
                           PropertyAttributes attributes);

Handle<Object> ForceSetProperty(Handle<JSObject> object,
                                Handle<Object> key,
                                Handle<Object> value,
                                PropertyAttributes attributes);

Handle<Object> SetNormalizedProperty(Handle<JSObject> object,
                                     Handle<String> key,
                                     Handle<Object> value,
                                     PropertyDetails details);

Handle<Object> ForceDeleteProperty(Handle<JSObject> object,
                                   Handle<Object> key);

Handle<Object> IgnoreAttributesAndSetLocalProperty(Handle<JSObject> object,
                                                   Handle<String> key,
                                                   Handle<Object> value,
    PropertyAttributes attributes);

Handle<Object> SetPropertyWithInterceptor(Handle<JSObject> object,
                                          Handle<String> key,
                                          Handle<Object> value,
                                          PropertyAttributes attributes);

Handle<Object> SetElement(Handle<JSObject> object,
                          uint32_t index,
                          Handle<Object> value);

Handle<Object> GetProperty(Handle<JSObject> obj,
                           const char* name);

Handle<Object> GetProperty(Handle<Object> obj,
                           Handle<Object> key);

Handle<Object> GetElement(Handle<Object> obj,
                          uint32_t index);

Handle<Object> GetPropertyWithInterceptor(Handle<JSObject> receiver,
                                          Handle<JSObject> holder,
                                          Handle<String> name,
                                          PropertyAttributes* attributes);

Handle<Object> GetPrototype(Handle<Object> obj);

Handle<Object> SetPrototype(Handle<JSObject> obj, Handle<Object> value);

// Return the object's hidden properties object. If the object has no hidden
// properties and create_if_needed is true, then a new hidden property object
// will be allocated. Otherwise the Heap::undefined_value is returned.
Handle<Object> GetHiddenProperties(Handle<JSObject> obj, bool create_if_needed);

Handle<Object> DeleteElement(Handle<JSObject> obj, uint32_t index);
Handle<Object> DeleteProperty(Handle<JSObject> obj, Handle<String> prop);

Handle<Object> LookupSingleCharacterStringFromCode(uint32_t index);

Handle<JSObject> Copy(Handle<JSObject> obj);

Handle<Object> SetAccessor(Handle<JSObject> obj, Handle<AccessorInfo> info);

Handle<FixedArray> AddKeysFromJSArray(Handle<FixedArray>,
                                      Handle<JSArray> array);

// Get the JS object corresponding to the given script; create it
// if none exists.
Handle<JSValue> GetScriptWrapper(Handle<Script> script);

// Script line number computations.
void InitScriptLineEnds(Handle<Script> script);
// For string calculates an array of line end positions. If the string
// does not end with a new line character, this character may optionally be
// imagined.
Handle<FixedArray> CalculateLineEnds(Handle<String> string,
                                     bool with_imaginary_last_new_line);
int GetScriptLineNumber(Handle<Script> script, int code_position);
// The safe version does not make heap allocations but may work much slower.
int GetScriptLineNumberSafe(Handle<Script> script, int code_position);

// Computes the enumerable keys from interceptors. Used for debug mirrors and
// by GetKeysInFixedArrayFor below.
v8::Handle<v8::Array> GetKeysForNamedInterceptor(Handle<JSObject> receiver,
                                                 Handle<JSObject> object);
v8::Handle<v8::Array> GetKeysForIndexedInterceptor(Handle<JSObject> receiver,
                                                   Handle<JSObject> object);

enum KeyCollectionType { LOCAL_ONLY, INCLUDE_PROTOS };

// Computes the enumerable keys for a JSObject. Used for implementing
// "for (n in object) { }".
Handle<FixedArray> GetKeysInFixedArrayFor(Handle<JSObject> object,
                                          KeyCollectionType type);
Handle<JSArray> GetKeysFor(Handle<JSObject> object);
Handle<FixedArray> GetEnumPropertyKeys(Handle<JSObject> object,
                                       bool cache_result);

// Computes the union of keys and return the result.
// Used for implementing "for (n in object) { }"
Handle<FixedArray> UnionOfKeys(Handle<FixedArray> first,
                               Handle<FixedArray> second);

Handle<String> SubString(Handle<String> str,
                         int start,
                         int end,
                         PretenureFlag pretenure = NOT_TENURED);


// Sets the expected number of properties for the function's instances.
void SetExpectedNofProperties(Handle<JSFunction> func, int nof);

// Sets the prototype property for a function instance.
void SetPrototypeProperty(Handle<JSFunction> func, Handle<JSObject> value);

// Sets the expected number of properties based on estimate from compiler.
void SetExpectedNofPropertiesFromEstimate(Handle<SharedFunctionInfo> shared,
                                          int estimate);


Handle<JSGlobalProxy> ReinitializeJSGlobalProxy(
    Handle<JSFunction> constructor,
    Handle<JSGlobalProxy> global);

Handle<Object> SetPrototype(Handle<JSFunction> function,
                            Handle<Object> prototype);


// Does lazy compilation of the given function. Returns true on success and
// false if the compilation resulted in a stack overflow.
enum ClearExceptionFlag { KEEP_EXCEPTION, CLEAR_EXCEPTION };

bool EnsureCompiled(Handle<SharedFunctionInfo> shared,
                    ClearExceptionFlag flag);

bool CompileLazyShared(Handle<SharedFunctionInfo> shared,
                       ClearExceptionFlag flag);

bool CompileLazy(Handle<JSFunction> function,
                 Handle<Object> receiver,
                 ClearExceptionFlag flag);

bool CompileLazyInLoop(Handle<JSFunction> function,
                       Handle<Object> receiver,
                       ClearExceptionFlag flag);

class NoHandleAllocation BASE_EMBEDDED {
 public:
#ifndef DEBUG
  NoHandleAllocation() {}
  ~NoHandleAllocation() {}
#else
  inline NoHandleAllocation();
  inline ~NoHandleAllocation();
 private:
  int extensions_;
#endif
};


// ----------------------------------------------------------------------------


// Stack allocated wrapper call for optimizing adding multiple
// properties to an object.
class OptimizedObjectForAddingMultipleProperties BASE_EMBEDDED {
 public:
  OptimizedObjectForAddingMultipleProperties(Handle<JSObject> object,
                                             int expected_property_count,
                                             bool condition = true);
  ~OptimizedObjectForAddingMultipleProperties();
 private:
  bool has_been_transformed_;  // Tells whether the object has been transformed.
  int unused_property_fields_;  // Captures the unused number of field.
  Handle<JSObject> object_;    // The object being optimized.
};


} }  // namespace v8::internal

#endif  // V8_HANDLES_H_