src/contexts.h

// Copyright 2006-2008 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
//       copyright notice, this list of conditions and the following
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//       with the distribution.
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#ifndef V8_CONTEXTS_H_
#define V8_CONTEXTS_H_

namespace v8 {
namespace internal {


enum ContextLookupFlags {
  FOLLOW_CONTEXT_CHAIN = 1,
  FOLLOW_PROTOTYPE_CHAIN = 2,

  DONT_FOLLOW_CHAINS = 0,
  FOLLOW_CHAINS = FOLLOW_CONTEXT_CHAIN | FOLLOW_PROTOTYPE_CHAIN
};


// Heap-allocated activation contexts.
//
// Contexts are implemented as FixedArray objects; the Context
// class is a convenience interface casted on a FixedArray object.
//
// Note: Context must have no virtual functions and Context objects
// must always be allocated via Heap::AllocateContext() or
// Factory::NewContext.

// Comment for special_function_table:
// Table for providing optimized/specialized functions.
// The array contains triplets [object, general_function, optimized_function].
// Primarily added to support built-in optimized variants of
// Array.prototype.{push,pop}.

#define GLOBAL_CONTEXT_FIELDS(V) \
  V(GLOBAL_PROXY_INDEX, JSObject, global_proxy_object) \
  V(SECURITY_TOKEN_INDEX, Object, security_token) \
  V(BOOLEAN_FUNCTION_INDEX, JSFunction, boolean_function) \
  V(NUMBER_FUNCTION_INDEX, JSFunction, number_function) \
  V(STRING_FUNCTION_INDEX, JSFunction, string_function) \
  V(OBJECT_FUNCTION_INDEX, JSFunction, object_function) \
  V(ARRAY_FUNCTION_INDEX, JSFunction, array_function) \
  V(DATE_FUNCTION_INDEX, JSFunction, date_function) \
  V(JSON_OBJECT_INDEX, JSObject, json_object) \
  V(REGEXP_FUNCTION_INDEX, JSFunction, regexp_function) \
  V(INITIAL_OBJECT_PROTOTYPE_INDEX, JSObject, initial_object_prototype) \
  V(CREATE_DATE_FUN_INDEX, JSFunction,  create_date_fun) \
  V(TO_NUMBER_FUN_INDEX, JSFunction, to_number_fun) \
  V(TO_STRING_FUN_INDEX, JSFunction, to_string_fun) \
  V(TO_DETAIL_STRING_FUN_INDEX, JSFunction, to_detail_string_fun) \
  V(TO_OBJECT_FUN_INDEX, JSFunction, to_object_fun) \
  V(TO_INTEGER_FUN_INDEX, JSFunction, to_integer_fun) \
  V(TO_UINT32_FUN_INDEX, JSFunction, to_uint32_fun) \
  V(TO_INT32_FUN_INDEX, JSFunction, to_int32_fun) \
  V(TO_BOOLEAN_FUN_INDEX, JSFunction, to_boolean_fun) \
  V(INSTANTIATE_FUN_INDEX, JSFunction, instantiate_fun) \
  V(CONFIGURE_INSTANCE_FUN_INDEX, JSFunction, configure_instance_fun) \
  V(FUNCTION_MAP_INDEX, Map, function_map) \
  V(FUNCTION_INSTANCE_MAP_INDEX, Map, function_instance_map) \
  V(JS_ARRAY_MAP_INDEX, Map, js_array_map)\
  V(SPECIAL_FUNCTION_TABLE_INDEX, FixedArray, special_function_table) \
  V(ARGUMENTS_BOILERPLATE_INDEX, JSObject, arguments_boilerplate) \
  V(MESSAGE_LISTENERS_INDEX, JSObject, message_listeners) \
  V(MAKE_MESSAGE_FUN_INDEX, JSFunction, make_message_fun) \
  V(GET_STACK_TRACE_LINE_INDEX, JSFunction, get_stack_trace_line_fun) \
  V(CONFIGURE_GLOBAL_INDEX, JSFunction, configure_global_fun) \
  V(FUNCTION_CACHE_INDEX, JSObject, function_cache) \
  V(RUNTIME_CONTEXT_INDEX, Context, runtime_context) \
  V(CALL_AS_FUNCTION_DELEGATE_INDEX, JSFunction, call_as_function_delegate) \
  V(CALL_AS_CONSTRUCTOR_DELEGATE_INDEX, JSFunction, \
    call_as_constructor_delegate) \
  V(EMPTY_SCRIPT_INDEX, Script, empty_script) \
  V(SCRIPT_FUNCTION_INDEX, JSFunction, script_function) \
  V(CONTEXT_EXTENSION_FUNCTION_INDEX, JSFunction, context_extension_function) \
  V(OUT_OF_MEMORY_INDEX, Object, out_of_memory) \
  V(MAP_CACHE_INDEX, Object, map_cache) \
  V(CONTEXT_DATA_INDEX, Object, data)

// JSFunctions are pairs (context, function code), sometimes also called
// closures. A Context object is used to represent function contexts and
// dynamically pushed 'with' contexts (or 'scopes' in ECMA-262 speak).
//
// At runtime, the contexts build a stack in parallel to the execution
// stack, with the top-most context being the current context. All contexts
// have the following slots:
//
// [ closure   ]  This is the current function. It is the same for all
//                contexts inside a function. It provides access to the
//                incoming context (i.e., the outer context, which may
//                or may not become the current function's context), and
//                it provides access to the functions code and thus it's
//                scope information, which in turn contains the names of
//                statically allocated context slots. The names are needed
//                for dynamic lookups in the presence of 'with' or 'eval'.
//
// [ fcontext  ]  A pointer to the innermost enclosing function context.
//                It is the same for all contexts *allocated* inside a
//                function, and the function context's fcontext points
//                to itself. It is only needed for fast access of the
//                function context (used for declarations, and static
//                context slot access).
//
// [ previous  ]  A pointer to the previous context. It is NULL for
//                function contexts, and non-NULL for 'with' contexts.
//                Used to implement the 'with' statement.
//
// [ extension ]  A pointer to an extension JSObject, or NULL. Used to
//                implement 'with' statements and dynamic declarations
//                (through 'eval'). The object in a 'with' statement is
//                stored in the extension slot of a 'with' context.
//                Dynamically declared variables/functions are also added
//                to lazily allocated extension object. Context::Lookup
//                searches the extension object for properties.
//
// [ global    ]  A pointer to the global object. Provided for quick
//                access to the global object from inside the code (since
//                we always have a context pointer).
//
// In addition, function contexts may have statically allocated context slots
// to store local variables/functions that are accessed from inner functions
// (via static context addresses) or through 'eval' (dynamic context lookups).
// Finally, the global context contains additional slots for fast access to
// global properties.
//
// We may be able to simplify the implementation:
//
// - We may be able to get rid of 'fcontext': We can always use the fact that
//   previous == NULL for function contexts and so we can search for them. They
//   are only needed when doing dynamic declarations, and the context chains
//   tend to be very very short (depth of nesting of 'with' statements). At
//   the moment we also use it in generated code for context slot accesses -
//   and there we don't want a loop because of code bloat - but we may not
//   need it there after all (see comment in codegen_*.cc).
//
// - If we cannot get rid of fcontext, consider making 'previous' never NULL
//   except for the global context. This could simplify Context::Lookup.

class Context: public FixedArray {
 public:
  // Conversions.
  static Context* cast(Object* context) {
    ASSERT(context->IsContext());
    return reinterpret_cast<Context*>(context);
  }

  // The default context slot layout; indices are FixedArray slot indices.
  enum {
    // These slots are in all contexts.
    CLOSURE_INDEX,
    FCONTEXT_INDEX,
    PREVIOUS_INDEX,
    EXTENSION_INDEX,
    GLOBAL_INDEX,
    MIN_CONTEXT_SLOTS,

    // These slots are only in global contexts.
    GLOBAL_PROXY_INDEX = MIN_CONTEXT_SLOTS,
    SECURITY_TOKEN_INDEX,
    ARGUMENTS_BOILERPLATE_INDEX,
    JS_ARRAY_MAP_INDEX,
    FUNCTION_MAP_INDEX,
    FUNCTION_INSTANCE_MAP_INDEX,
    INITIAL_OBJECT_PROTOTYPE_INDEX,
    BOOLEAN_FUNCTION_INDEX,
    NUMBER_FUNCTION_INDEX,
    STRING_FUNCTION_INDEX,
    OBJECT_FUNCTION_INDEX,
    ARRAY_FUNCTION_INDEX,
    DATE_FUNCTION_INDEX,
    JSON_OBJECT_INDEX,
    REGEXP_FUNCTION_INDEX,
    CREATE_DATE_FUN_INDEX,
    TO_NUMBER_FUN_INDEX,
    TO_STRING_FUN_INDEX,
    TO_DETAIL_STRING_FUN_INDEX,
    TO_OBJECT_FUN_INDEX,
    TO_INTEGER_FUN_INDEX,
    TO_UINT32_FUN_INDEX,
    TO_INT32_FUN_INDEX,
    TO_BOOLEAN_FUN_INDEX,
    INSTANTIATE_FUN_INDEX,
    CONFIGURE_INSTANCE_FUN_INDEX,
    SPECIAL_FUNCTION_TABLE_INDEX,
    MESSAGE_LISTENERS_INDEX,
    MAKE_MESSAGE_FUN_INDEX,
    GET_STACK_TRACE_LINE_INDEX,
    CONFIGURE_GLOBAL_INDEX,
    FUNCTION_CACHE_INDEX,
    RUNTIME_CONTEXT_INDEX,
    CALL_AS_FUNCTION_DELEGATE_INDEX,
    CALL_AS_CONSTRUCTOR_DELEGATE_INDEX,
    EMPTY_SCRIPT_INDEX,
    SCRIPT_FUNCTION_INDEX,
    CONTEXT_EXTENSION_FUNCTION_INDEX,
    OUT_OF_MEMORY_INDEX,
    MAP_CACHE_INDEX,
    CONTEXT_DATA_INDEX,
    GLOBAL_CONTEXT_SLOTS
  };

  // Direct slot access.
  JSFunction* closure() { return JSFunction::cast(get(CLOSURE_INDEX)); }
  void set_closure(JSFunction* closure) { set(CLOSURE_INDEX, closure); }

  Context* fcontext() { return Context::cast(get(FCONTEXT_INDEX)); }
  void set_fcontext(Context* context) { set(FCONTEXT_INDEX, context); }

  Context* previous() {
    Object* result = unchecked_previous();
    ASSERT(IsBootstrappingOrContext(result));
    return reinterpret_cast<Context*>(result);
  }
  void set_previous(Context* context) { set(PREVIOUS_INDEX, context); }

  bool has_extension() { return unchecked_extension() != NULL; }
  JSObject* extension() { return JSObject::cast(unchecked_extension()); }
  void set_extension(JSObject* object) { set(EXTENSION_INDEX, object); }

  GlobalObject* global() {
    Object* result = get(GLOBAL_INDEX);
    ASSERT(IsBootstrappingOrGlobalObject(result));
    return reinterpret_cast<GlobalObject*>(result);
  }
  void set_global(GlobalObject* global) { set(GLOBAL_INDEX, global); }

  // Returns a JSGlobalProxy object or null.
  JSObject* global_proxy();
  void set_global_proxy(JSObject* global);

  // The builtins object.
  JSBuiltinsObject* builtins();

  // Compute the global context by traversing the context chain.
  Context* global_context();

  // Tells if this is a function context (as opposed to a 'with' context).
  bool is_function_context() { return unchecked_previous() == NULL; }

  // Tells whether the global context is marked with out of memory.
  bool has_out_of_memory() {
    return global_context()->out_of_memory() == Heap::true_value();
  }

  // Mark the global context with out of memory.
  void mark_out_of_memory() {
    global_context()->set_out_of_memory(Heap::true_value());
  }

  // The exception holder is the object used as a with object in
  // the implementation of a catch block.
  bool is_exception_holder(Object* object) {
    return IsCatchContext() && extension() == object;
  }

#define GLOBAL_CONTEXT_FIELD_ACCESSORS(index, type, name) \
  void  set_##name(type* value) {                         \
    ASSERT(IsGlobalContext());                            \
    set(index, value);                                    \
  }                                                       \
  type* name() {                                          \
    ASSERT(IsGlobalContext());                            \
    return type::cast(get(index));                        \
  }
  GLOBAL_CONTEXT_FIELDS(GLOBAL_CONTEXT_FIELD_ACCESSORS)
#undef GLOBAL_CONTEXT_FIELD_ACCESSORS

  // Lookup the the slot called name, starting with the current context.
  // There are 4 possible outcomes:
  //
  // 1) index_ >= 0 && result->IsContext():
  //    most common case, the result is a Context, and index is the
  //    context slot index, and the slot exists.
  //    attributes == READ_ONLY for the function name variable, NONE otherwise.
  //
  // 2) index_ >= 0 && result->IsJSObject():
  //    the result is the JSObject arguments object, the index is the parameter
  //    index, i.e., key into the arguments object, and the property exists.
  //    attributes != ABSENT.
  //
  // 3) index_ < 0 && result->IsJSObject():
  //    the result is the JSObject extension context or the global object,
  //    and the name is the property name, and the property exists.
  //    attributes != ABSENT.
  //
  // 4) index_ < 0 && result.is_null():
  //    there was no context found with the corresponding property.
  //    attributes == ABSENT.
  Handle<Object> Lookup(Handle<String> name, ContextLookupFlags flags,
                        int* index_, PropertyAttributes* attributes);

  // Determine if a local variable with the given name exists in a
  // context.  Do not consider context extension objects.  This is
  // used for compiling code using eval.  If the context surrounding
  // the eval call does not have a local variable with this name and
  // does not contain a with statement the property is global unless
  // it is shadowed by a property in an extension object introduced by
  // eval.
  bool GlobalIfNotShadowedByEval(Handle<String> name);

  // Code generation support.
  static int SlotOffset(int index) {
    return kHeaderSize + index * kPointerSize - kHeapObjectTag;
  }

 private:
  // Unchecked access to the slots.
  Object* unchecked_previous() { return get(PREVIOUS_INDEX); }
  Object* unchecked_extension() { return get(EXTENSION_INDEX); }

#ifdef DEBUG
  // Bootstrapping-aware type checks.
  static bool IsBootstrappingOrContext(Object* object);
  static bool IsBootstrappingOrGlobalObject(Object* object);
#endif
};

} }  // namespace v8::internal

#endif  // V8_CONTEXTS_H_