C++ ArenaHeader::getAllocKind方法代码示例

void
GCMarker::processMarkStackOther(SliceBudget &budget, uintptr_t tag, uintptr_t addr)
{
    if (tag == TypeTag) {
        ScanTypeObject(this, reinterpret_cast<types::TypeObject *>(addr));
    } else if (tag == SavedValueArrayTag) {
        JS_ASSERT(!(addr & Cell::CellMask));
        JSObject *obj = reinterpret_cast<JSObject *>(addr);
        HeapValue *vp, *end;
        if (restoreValueArray(obj, (void **)&vp, (void **)&end))
            pushValueArray(obj, vp, end);
        else
            pushObject(obj);
    } else if (tag == IonCodeTag) {
        MarkChildren(this, reinterpret_cast<ion::IonCode *>(addr));
    } else if (tag == ArenaTag) {
        ArenaHeader *aheader = reinterpret_cast<ArenaHeader *>(addr);
        AllocKind thingKind = aheader->getAllocKind();
        size_t thingSize = Arena::thingSize(thingKind);

        for ( ; aheader; aheader = aheader->next) {
            Arena *arena = aheader->getArena();
            FreeSpan firstSpan(aheader->getFirstFreeSpan());
            const FreeSpan *span = &firstSpan;

            for (uintptr_t thing = arena->thingsStart(thingKind); ; thing += thingSize) {
                JS_ASSERT(thing <= arena->thingsEnd());
                if (thing == span->first) {
                    if (!span->hasNext())
                        break;
                    thing = span->last;
                    span = span->nextSpan();
                } else {
                    JSObject *object = reinterpret_cast<JSObject *>(thing);
                    if (object->hasSingletonType() && object->markIfUnmarked(getMarkColor()))
                        pushObject(object);
                    budget.step();
                }
            }
            if (budget.isOverBudget()) {
                pushArenaList(aheader);
                return;
            }
        }
    }

#if JS_HAS_XML_SUPPORT
    else {
        JS_ASSERT(tag == XmlTag);
        MarkChildren(this, reinterpret_cast<JSXML *>(addr));
    }
#endif
}

/*
 * Tests whether w is a (possibly dead) GC thing. Returns CGCT_VALID and
 * details about the thing if so. On failure, returns the reason for rejection.
 */
static inline ConservativeGCTest
IsAddressableGCThing(JSRuntime *rt, uintptr_t w,
                     bool skipUncollectedCompartments,
                     gc::AllocKind *thingKindPtr,
                     ArenaHeader **arenaHeader,
                     void **thing)
{
    /*
     * We assume that the compiler never uses sub-word alignment to store
     * pointers and does not tag pointers on its own. Additionally, the value
     * representation for all values and the jsid representation for GC-things
     * do not touch the low two bits. Thus any word with the low two bits set
     * is not a valid GC-thing.
     */
    JS_STATIC_ASSERT(JSID_TYPE_STRING == 0 && JSID_TYPE_OBJECT == 4);
    if (w & 0x3)
        return CGCT_LOWBITSET;

    /*
     * An object jsid has its low bits tagged. In the value representation on
     * 64-bit, the high bits are tagged.
     */
    const uintptr_t JSID_PAYLOAD_MASK = ~uintptr_t(JSID_TYPE_MASK);
#if JS_BITS_PER_WORD == 32
    uintptr_t addr = w & JSID_PAYLOAD_MASK;
#elif JS_BITS_PER_WORD == 64
    uintptr_t addr = w & JSID_PAYLOAD_MASK & JSVAL_PAYLOAD_MASK;
#endif

    Chunk *chunk = Chunk::fromAddress(addr);

    if (!rt->gcChunkSet.has(chunk))
        return CGCT_NOTCHUNK;

    /*
     * We query for pointers outside the arena array after checking for an
     * allocated chunk. Such pointers are rare and we want to reject them
     * after doing more likely rejections.
     */
    if (!Chunk::withinArenasRange(addr))
        return CGCT_NOTARENA;

    /* If the arena is not currently allocated, don't access the header. */
    size_t arenaOffset = Chunk::arenaIndex(addr);
    if (chunk->decommittedArenas.get(arenaOffset))
        return CGCT_FREEARENA;

    ArenaHeader *aheader = &chunk->arenas[arenaOffset].aheader;

    if (!aheader->allocated())
        return CGCT_FREEARENA;

    if (skipUncollectedCompartments && !aheader->zone->isCollecting())
        return CGCT_OTHERCOMPARTMENT;

    AllocKind thingKind = aheader->getAllocKind();
    uintptr_t offset = addr & ArenaMask;
    uintptr_t minOffset = Arena::firstThingOffset(thingKind);
    if (offset < minOffset)
        return CGCT_NOTARENA;

    /* addr can point inside the thing so we must align the address. */
    uintptr_t shift = (offset - minOffset) % Arena::thingSize(thingKind);
    addr -= shift;

    if (thing)
        *thing = reinterpret_cast<void *>(addr);
    if (arenaHeader)
        *arenaHeader = aheader;
    if (thingKindPtr)
        *thingKindPtr = thingKind;
    return CGCT_VALID;
}