C++ ArenaHeader类代码示例

bool
GCMarker::markDelayedChildren(SliceBudget& budget)
{
    GCRuntime& gc = runtime()->gc;
    gcstats::AutoPhase ap(gc.stats, gc.state() == MARK, gcstats::PHASE_MARK_DELAYED);

    MOZ_ASSERT(unmarkedArenaStackTop);
    do {
        /*
         * If marking gets delayed at the same arena again, we must repeat
         * marking of its things. For that we pop arena from the stack and
         * clear its hasDelayedMarking flag before we begin the marking.
         */
        ArenaHeader* aheader = unmarkedArenaStackTop;
        MOZ_ASSERT(aheader->hasDelayedMarking);
        MOZ_ASSERT(markLaterArenas);
        unmarkedArenaStackTop = aheader->getNextDelayedMarking();
        aheader->unsetDelayedMarking();
        markLaterArenas--;
        markDelayedChildren(aheader);

        budget.step(150);
        if (budget.isOverBudget())
            return false;
    } while (unmarkedArenaStackTop);
    MOZ_ASSERT(!markLaterArenas);

    return true;
}

void
js::IterateZonesCompartmentsArenasCells(JSRuntime *rt, void *data,
                                        IterateZoneCallback zoneCallback,
                                        JSIterateCompartmentCallback compartmentCallback,
                                        IterateArenaCallback arenaCallback,
                                        IterateCellCallback cellCallback)
{
    AutoPrepareForTracing prop(rt);

    for (ZonesIter zone(rt); !zone.done(); zone.next()) {
        (*zoneCallback)(rt, data, zone);

        for (CompartmentsInZoneIter comp(zone); !comp.done(); comp.next())
            (*compartmentCallback)(rt, data, comp);

        for (size_t thingKind = 0; thingKind != FINALIZE_LIMIT; thingKind++) {
            JSGCTraceKind traceKind = MapAllocToTraceKind(AllocKind(thingKind));
            size_t thingSize = Arena::thingSize(AllocKind(thingKind));

            for (ArenaIter aiter(zone, AllocKind(thingKind)); !aiter.done(); aiter.next()) {
                ArenaHeader *aheader = aiter.get();
                (*arenaCallback)(rt, data, aheader->getArena(), traceKind, thingSize);
                for (CellIterUnderGC iter(aheader); !iter.done(); iter.next())
                    (*cellCallback)(rt, data, iter.getCell(), traceKind, thingSize);
            }
        }
    }
}

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
}

TenuredCell *
ArenaLists::allocateFromArena(JS::Zone *zone, AllocKind thingKind,
                              AutoMaybeStartBackgroundAllocation &maybeStartBGAlloc)
{
    JSRuntime *rt = zone->runtimeFromAnyThread();
    Maybe<AutoLockGC> maybeLock;

    // See if we can proceed without taking the GC lock.
    if (backgroundFinalizeState[thingKind] != BFS_DONE)
        maybeLock.emplace(rt);

    ArenaList &al = arenaLists[thingKind];
    ArenaHeader *aheader = al.takeNextArena();
    if (aheader) {
        // Empty arenas should be immediately freed.
        MOZ_ASSERT(!aheader->isEmpty());

        return allocateFromArenaInner<HasFreeThings>(zone, aheader, thingKind);
    }

    // Parallel threads have their own ArenaLists, but chunks are shared;
    // if we haven't already, take the GC lock now to avoid racing.
    if (maybeLock.isNothing())
        maybeLock.emplace(rt);

    Chunk *chunk = rt->gc.pickChunk(maybeLock.ref(), maybeStartBGAlloc);
    if (!chunk)
        return nullptr;

    // Although our chunk should definitely have enough space for another arena,
    // there are other valid reasons why Chunk::allocateArena() may fail.
    aheader = rt->gc.allocateArena(chunk, zone, thingKind, maybeLock.ref());
    if (!aheader)
        return nullptr;

    MOZ_ASSERT(!maybeLock->wasUnlocked());
    MOZ_ASSERT(al.isCursorAtEnd());
    al.insertAtCursor(aheader);

    return allocateFromArenaInner<IsEmpty>(zone, aheader, thingKind);
}

void
GCMarker::reset()
{
    color = BLACK;

    stack.reset();
    MOZ_ASSERT(isMarkStackEmpty());

    while (unmarkedArenaStackTop) {
        ArenaHeader* aheader = unmarkedArenaStackTop;
        MOZ_ASSERT(aheader->hasDelayedMarking);
        MOZ_ASSERT(markLaterArenas);
        unmarkedArenaStackTop = aheader->getNextDelayedMarking();
        aheader->unsetDelayedMarking();
        aheader->markOverflow = 0;
        aheader->allocatedDuringIncremental = 0;
        markLaterArenas--;
    }
    MOZ_ASSERT(isDrained());
    MOZ_ASSERT(!markLaterArenas);
}

/*
 * 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;
}