/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sw=4 et tw=78:
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef ObjectImpl_h___
#define ObjectImpl_h___

#include "mozilla/Assertions.h"
#include "mozilla/StandardInteger.h"

#include "jsfriendapi.h"
#include "jsinfer.h"
#include "jsval.h"

#include "gc/Barrier.h"

namespace js {

/*
 * Header structure for object element arrays. This structure is immediately
 * followed by an array of elements, with the elements member in an object
 * pointing to the beginning of that array (the end of this structure).
 * See below for usage of this structure.
 */
class ObjectElements
{
    friend struct ::JSObject;

    /* Number of allocated slots. */
    uint32_t capacity;

    /*
     * Number of initialized elements. This is <= the capacity, and for arrays
     * is <= the length. Memory for elements above the initialized length is
     * uninitialized, but values between the initialized length and the proper
     * length are conceptually holes.
     */
    uint32_t initializedLength;

    /* 'length' property of array objects, unused for other objects. */
    uint32_t length;

    /* :XXX: bug 586842 store state about sparse slots. */
    uint32_t unused;

    void staticAsserts() {
        MOZ_STATIC_ASSERT(sizeof(ObjectElements) == VALUES_PER_HEADER * sizeof(Value),
                          "Elements size and values-per-Elements mismatch");
    }

  public:

    ObjectElements(uint32_t capacity, uint32_t length)
      : capacity(capacity), initializedLength(0), length(length)
    {}

    HeapSlot *elements() { return (HeapSlot *)(uintptr_t(this) + sizeof(ObjectElements)); }
    static ObjectElements * fromElements(HeapSlot *elems) {
        return (ObjectElements *)(uintptr_t(elems) - sizeof(ObjectElements));
    }

    static int offsetOfCapacity() {
        return (int)offsetof(ObjectElements, capacity) - (int)sizeof(ObjectElements);
    }
    static int offsetOfInitializedLength() {
        return (int)offsetof(ObjectElements, initializedLength) - (int)sizeof(ObjectElements);
    }
    static int offsetOfLength() {
        return (int)offsetof(ObjectElements, length) - (int)sizeof(ObjectElements);
    }

    static const size_t VALUES_PER_HEADER = 2;
};

/* Shared singleton for objects with no elements. */
extern HeapSlot *emptyObjectElements;

struct Class;
struct GCMarker;
struct ObjectOps;
struct Shape;

class NewObjectCache;

/*
 * ObjectImpl specifies the internal implementation of an object.  (In contrast
 * JSObject specifies an "external" interface, at the conceptual level of that
 * exposed in ECMAScript.)
 *
 * The |shape_| member stores the shape of the object, which includes the
 * object's class and the layout of all its properties.
 *
 * The type member stores the type of the object, which contains its prototype
 * object and the possible types of its properties.
 *
 * The rest of the object stores its named properties and indexed elements.
 * These are stored separately from one another. Objects are followed by an
 * variable-sized array of values for inline storage, which may be used by
 * either properties of native objects (fixed slots) or by elements.
 *
 * Two native objects with the same shape are guaranteed to have the same
 * number of fixed slots.
 *
 * Named property storage can be split between fixed slots and a dynamically
 * allocated array (the slots member). For an object with N fixed slots, shapes
 * with slots [0..N-1] are stored in the fixed slots, and the remainder are
 * stored in the dynamic array. If all properties fit in the fixed slots, the
 * 'slots' member is NULL.
 *
 * Elements are indexed via the 'elements' member. This member can point to
 * either the shared emptyObjectElements singleton, into the inline value array
 * (the address of the third value, to leave room for a ObjectElements header;
 * in this case numFixedSlots() is zero) or to a dynamically allocated array.
 *
 * Only certain combinations of properties and elements storage are currently
 * possible. This will be changing soon :XXX: bug 586842.
 *
 * - For objects other than arrays and typed arrays, the elements are empty.
 *
 * - For 'slow' arrays, both elements and properties are used, but the
 *   elements have zero capacity --- only the length member is used.
 *
 * - For dense arrays, elements are used and properties are not used.
 *
 * - For typed array buffers, elements are used and properties are not used.
 *   The data indexed by the elements do not represent Values, but primitive
 *   unboxed integers or floating point values.
 *
 * The members of this class are currently protected; in the long run this will
 * will change so that some members are private, and only certain methods that
 * act upon them will be protected.
 */
class ObjectImpl : public gc::Cell
{
  protected:
    /*
     * Shape of the object, encodes the layout of the object's properties and
     * all other information about its structure. See jsscope.h.
     */
    HeapPtrShape shape_;

    /*
     * The object's type and prototype. For objects with the LAZY_TYPE flag
     * set, this is the prototype's default 'new' type and can only be used
     * to get that prototype.
     */
    HeapPtrTypeObject type_;

    HeapSlot *slots;     /* Slots for object properties. */
    HeapSlot *elements;  /* Slots for object elements. */

  private:
    static void staticAsserts() {
        MOZ_STATIC_ASSERT(sizeof(ObjectImpl) == sizeof(shadow::Object),
                          "shadow interface must match actual implementation");
        MOZ_STATIC_ASSERT(sizeof(ObjectImpl) % sizeof(Value) == 0,
                          "fixed slots after an object must be aligned");

        MOZ_STATIC_ASSERT(offsetof(ObjectImpl, shape_) == offsetof(shadow::Object, shape),
                          "shadow shape must match actual shape");
        MOZ_STATIC_ASSERT(offsetof(ObjectImpl, type_) == offsetof(shadow::Object, type),
                          "shadow type must match actual type");
        MOZ_STATIC_ASSERT(offsetof(ObjectImpl, slots) == offsetof(shadow::Object, slots),
                          "shadow slots must match actual slots");
        MOZ_STATIC_ASSERT(offsetof(ObjectImpl, elements) == offsetof(shadow::Object, _1),
                          "shadow placeholder must match actual elements");
    }

    JSObject * asObjectPtr() { return reinterpret_cast<JSObject *>(this); }

  protected:
    friend struct GCMarker;
    friend struct Shape;
    friend class NewObjectCache;

    /* Minimum size for dynamically allocated slots. */
    static const uint32_t SLOT_CAPACITY_MIN = 8;

    HeapSlot *fixedSlots() const {
        return reinterpret_cast<HeapSlot *>(uintptr_t(this) + sizeof(ObjectImpl));
    }

    /*
     * These functions are currently public for simplicity; in the long run
     * it may make sense to make at least some of them private.
     */

  public:
    Shape * lastProperty() const {
        MOZ_ASSERT(shape_);
        return shape_;
    }

    types::TypeObject *type() const {
        MOZ_ASSERT(!hasLazyType());
        return type_;
    }

    size_t numFixedSlots() const {
        return reinterpret_cast<const shadow::Object *>(this)->numFixedSlots();
    }

    /*
     * Whether this is the only object which has its specified type. This
     * object will have its type constructed lazily as needed by analysis.
     */
    bool hasSingletonType() const { return !!type_->singleton; }

    /*
     * Whether the object's type has not been constructed yet. If an object
     * might have a lazy type, use getType() below, otherwise type().
     */
    bool hasLazyType() const { return type_->lazy(); }

    inline bool isNative() const;

    const Shape * nativeLookup(JSContext *cx, jsid id);

    inline Class *getClass() const;
    inline JSClass *getJSClass() const;
    inline bool hasClass(const Class *c) const;
    inline const ObjectOps *getOps() const;

    /*
     * An object is a delegate if it is on another object's prototype or scope
     * chain, and therefore the delegate might be asked implicitly to get or
     * set a property on behalf of another object. Delegates may be accessed
     * directly too, as may any object, but only those objects linked after the
     * head of any prototype or scope chain are flagged as delegates. This
     * definition helps to optimize shape-based property cache invalidation
     * (see Purge{Scope,Proto}Chain in jsobj.cpp).
     */
    inline bool isDelegate() const;

    /*
     * Return true if this object is a native one that has been converted from
     * shared-immutable prototype-rooted shape storage to dictionary-shapes in
     * a doubly-linked list.
     */
    inline bool inDictionaryMode() const;

    /*
     * Get the number of dynamic slots to allocate to cover the properties in
     * an object with the given number of fixed slots and slot span. The slot
     * capacity is not stored explicitly, and the allocated size of the slot
     * array is kept in sync with this count.
     */
    static inline size_t dynamicSlotsCount(size_t nfixed, size_t span);

    /* Memory usage functions. */
    inline size_t sizeOfThis() const;

    /* Elements accessors. */

    ObjectElements * getElementsHeader() const {
        return ObjectElements::fromElements(elements);
    }

    inline HeapSlot *fixedElements() const {
        MOZ_STATIC_ASSERT(2 * sizeof(Value) == sizeof(ObjectElements),
                          "when elements are stored inline, the first two "
                          "slots will hold the ObjectElements header");
        return &fixedSlots()[2];
    }

    void setFixedElements() { this->elements = fixedElements(); }

    inline bool hasDynamicElements() const {
        /*
         * Note: for objects with zero fixed slots this could potentially give
         * a spurious 'true' result, if the end of this object is exactly
         * aligned with the end of its arena and dynamic slots are allocated
         * immediately afterwards. Such cases cannot occur for dense arrays
         * (which have at least two fixed slots) and can only result in a leak.
         */
        return elements != emptyObjectElements && elements != fixedElements();
    }

    /* Write barrier support. */
    static inline void readBarrier(ObjectImpl *obj);
    static inline void writeBarrierPre(ObjectImpl *obj);
    static inline void writeBarrierPost(ObjectImpl *obj, void *addr);
    inline void privateWriteBarrierPre(void **oldval);
    inline void privateWriteBarrierPost(void **oldval);

    /* JIT Accessors */
    static size_t offsetOfShape() { return offsetof(ObjectImpl, shape_); }
    HeapPtrShape *addressOfShape() { return &shape_; }

    static size_t offsetOfType() { return offsetof(ObjectImpl, type_); }
    HeapPtrTypeObject *addressOfType() { return &type_; }

    static size_t offsetOfElements() { return offsetof(ObjectImpl, elements); }
    static size_t offsetOfFixedElements() {
        return sizeof(ObjectImpl) + sizeof(ObjectElements);
    }

    static size_t getFixedSlotOffset(size_t slot) {
        return sizeof(ObjectImpl) + slot * sizeof(Value);
    }
    static size_t getPrivateDataOffset(size_t nfixed) { return getFixedSlotOffset(nfixed); }
    static size_t offsetOfSlots() { return offsetof(ObjectImpl, slots); }

    /* These functions are public, and they should remain public. */

  public:
    JSObject * getProto() const {
        return type_->proto;
    }

    inline bool isExtensible() const;
};

} /* namespace js */

#endif /* ObjectImpl_h__ */