C++ JSCell类代码示例

EncodedJSValue JIT_OPERATION operationGetByVal(ExecState* exec, EncodedJSValue encodedBase, EncodedJSValue encodedProperty)
{
    VM& vm = exec->vm();
    NativeCallFrameTracer tracer(&vm, exec);
    
    JSValue baseValue = JSValue::decode(encodedBase);
    JSValue property = JSValue::decode(encodedProperty);

    if (LIKELY(baseValue.isCell())) {
        JSCell* base = baseValue.asCell();

        if (property.isUInt32()) {
            return getByVal(exec, base, property.asUInt32());
        } else if (property.isDouble()) {
            double propertyAsDouble = property.asDouble();
            uint32_t propertyAsUInt32 = static_cast<uint32_t>(propertyAsDouble);
            if (propertyAsUInt32 == propertyAsDouble)
                return getByVal(exec, base, propertyAsUInt32);
        } else if (property.isString()) {
            Structure& structure = *base->structure(vm);
            if (JSCell::canUseFastGetOwnProperty(structure)) {
                if (AtomicStringImpl* existingAtomicString = asString(property)->toExistingAtomicString(exec)) {
                    if (JSValue result = base->fastGetOwnProperty(vm, structure, existingAtomicString))
                        return JSValue::encode(result);
                }
            }
        }
    }

    PropertyName propertyName = property.toPropertyKey(exec);
    return JSValue::encode(baseValue.get(exec, propertyName));
}

void JSGlobalData::storeVPtrs()
{
    // Enough storage to fit a JSArray, JSByteArray, JSString, or JSFunction.
    // COMPILE_ASSERTS below check that this is true.
    char storage[64];

    COMPILE_ASSERT(sizeof(JSFinalObject) <= sizeof(storage), sizeof_JSFinalObject_must_be_less_than_storage);
    JSCell* jsFinalObject = new (storage) JSFinalObject(JSFinalObject::VPtrStealingHack);
    CLOBBER_MEMORY();
    JSGlobalData::jsFinalObjectVPtr = jsFinalObject->vptr();

    COMPILE_ASSERT(sizeof(JSArray) <= sizeof(storage), sizeof_JSArray_must_be_less_than_storage);
    JSCell* jsArray = new (storage) JSArray(JSArray::VPtrStealingHack);
    CLOBBER_MEMORY();
    JSGlobalData::jsArrayVPtr = jsArray->vptr();

    COMPILE_ASSERT(sizeof(JSByteArray) <= sizeof(storage), sizeof_JSByteArray_must_be_less_than_storage);
    JSCell* jsByteArray = new (storage) JSByteArray(JSByteArray::VPtrStealingHack);
    CLOBBER_MEMORY();
    JSGlobalData::jsByteArrayVPtr = jsByteArray->vptr();

    COMPILE_ASSERT(sizeof(JSString) <= sizeof(storage), sizeof_JSString_must_be_less_than_storage);
    JSCell* jsString = new (storage) JSString(JSString::VPtrStealingHack);
    CLOBBER_MEMORY();
    JSGlobalData::jsStringVPtr = jsString->vptr();

    COMPILE_ASSERT(sizeof(JSFunction) <= sizeof(storage), sizeof_JSFunction_must_be_less_than_storage);
    JSCell* jsFunction = new (storage) JSFunction(JSCell::VPtrStealingHack);
    CLOBBER_MEMORY();
    JSGlobalData::jsFunctionVPtr = jsFunction->vptr();
}

MarkedBlock::FreeList MarkedBlock::specializedSweep()
{
    ASSERT(blockState != Allocated && blockState != FreeListed);
    ASSERT(destructorCallNeeded || sweepMode != SweepOnly);

    // This produces a free list that is ordered in reverse through the block.
    // This is fine, since the allocation code makes no assumptions about the
    // order of the free list.
    FreeCell* head = 0;
    size_t count = 0;
    for (size_t i = firstAtom(); i < m_endAtom; i += m_atomsPerCell) {
        if (blockState == Marked && m_marks.get(i))
            continue;

        JSCell* cell = reinterpret_cast_ptr<JSCell*>(&atoms()[i]);
        if (blockState == Zapped && !cell->isZapped())
            continue;

        if (destructorCallNeeded && blockState != New)
            callDestructor(cell);

        if (sweepMode == SweepToFreeList) {
            FreeCell* freeCell = reinterpret_cast<FreeCell*>(cell);
            freeCell->next = head;
            head = freeCell;
            ++count;
        }
    }

    m_state = ((sweepMode == SweepToFreeList) ? FreeListed : Zapped);
    return FreeList(head, count * cellSize());
}

void JSGlobalData::releaseExecutableMemory()
{
    if (dynamicGlobalObject) {
        StackPreservingRecompiler recompiler;
        HashSet<JSCell*> roots;
        heap.getConservativeRegisterRoots(roots);
        HashSet<JSCell*>::iterator end = roots.end();
        for (HashSet<JSCell*>::iterator ptr = roots.begin(); ptr != end; ++ptr) {
            ScriptExecutable* executable = 0;
            JSCell* cell = *ptr;
            if (cell->inherits(&ScriptExecutable::s_info))
                executable = static_cast<ScriptExecutable*>(*ptr);
            else if (cell->inherits(&JSFunction::s_info)) {
                JSFunction* function = jsCast<JSFunction*>(*ptr);
                if (function->isHostFunction())
                    continue;
                executable = function->jsExecutable();
            } else
                continue;
            ASSERT(executable->inherits(&ScriptExecutable::s_info));
            executable->unlinkCalls();
            if (executable->inherits(&FunctionExecutable::s_info))
                recompiler.currentlyExecutingFunctions.add(static_cast<FunctionExecutable*>(executable));
                
        }
        heap.objectSpace().forEachCell<StackPreservingRecompiler>(recompiler);
    }
    m_regExpCache->invalidateCode();
    heap.collectAllGarbage();
}

void SlotVisitor::appendJSCellOrAuxiliary(HeapCell* heapCell)
{
    if (!heapCell)
        return;
    
    ASSERT(!m_isCheckingForDefaultMarkViolation);
    
    if (Heap::testAndSetMarked(m_markingVersion, heapCell))
        return;
    
    switch (heapCell->cellKind()) {
    case HeapCell::JSCell: {
        JSCell* jsCell = static_cast<JSCell*>(heapCell);
        
        if (!jsCell->structure()) {
            ASSERT_NOT_REACHED();
            return;
        }
        
        jsCell->setCellState(CellState::Grey);

        appendToMarkStack(jsCell);
        return;
    }
        
    case HeapCell::Auxiliary: {
        noteLiveAuxiliaryCell(heapCell);
        return;
    } }
}

void VM::releaseExecutableMemory()
{
    prepareToDiscardCode();

    if (entryScope) {
        StackPreservingRecompiler recompiler;
        HeapIterationScope iterationScope(heap);
        HashSet<JSCell*> roots;
        heap.getConservativeRegisterRoots(roots);
        HashSet<JSCell*>::iterator end = roots.end();
        for (HashSet<JSCell*>::iterator ptr = roots.begin(); ptr != end; ++ptr) {
            ScriptExecutable* executable = 0;
            JSCell* cell = *ptr;
            if (cell->inherits(ScriptExecutable::info()))
                executable = static_cast<ScriptExecutable*>(*ptr);
            else if (cell->inherits(JSFunction::info())) {
                JSFunction* function = jsCast<JSFunction*>(*ptr);
                if (function->isHostFunction())
                    continue;
                executable = function->jsExecutable();
            } else
                continue;
            ASSERT(executable->inherits(ScriptExecutable::info()));
            executable->unlinkCalls();
            if (executable->inherits(FunctionExecutable::info()))
                recompiler.currentlyExecutingFunctions.add(static_cast<FunctionExecutable*>(executable));

        }
        heap.objectSpace().forEachLiveCell<StackPreservingRecompiler>(iterationScope, recompiler);
    }
    m_regExpCache->invalidateCode();
    heap.collectAllGarbage();
}

void InspectorHeapAgent::getRemoteObject(ErrorString& errorString, int heapObjectId, const String* optionalObjectGroup, RefPtr<Inspector::Protocol::Runtime::RemoteObject>& result)
{
    // Prevent the cell from getting collected as we look it up.
    VM& vm = m_environment.vm();
    JSLockHolder lock(vm);
    DeferGC deferGC(vm.heap);

    unsigned heapObjectIdentifier = static_cast<unsigned>(heapObjectId);
    const Optional<HeapSnapshotNode> optionalNode = nodeForHeapObjectIdentifier(errorString, heapObjectIdentifier);
    if (!optionalNode)
        return;

    JSCell* cell = optionalNode->cell;
    Structure* structure = cell->structure(m_environment.vm());
    if (!structure) {
        errorString = ASCIILiteral("Unable to get object details");
        return;
    }

    JSGlobalObject* globalObject = structure->globalObject();
    if (!globalObject) {
        errorString = ASCIILiteral("Unable to get object details");
        return;
    }

    InjectedScript injectedScript = m_injectedScriptManager.injectedScriptFor(globalObject->globalExec());
    if (injectedScript.hasNoValue()) {
        errorString = ASCIILiteral("Unable to get object details - InjectedScript");
        return;
    }

    Deprecated::ScriptValue cellScriptValue(m_environment.vm(), JSValue(cell));
    String objectGroup = optionalObjectGroup ? *optionalObjectGroup : String();
    result = injectedScript.wrapObject(cellScriptValue, objectGroup, true);
}

bool JSObjectIsFunction(JSContextRef, JSObjectRef object)
{
    if (!object)
        return false;
    CallData callData;
    JSCell* cell = toJS(object);
    return cell->methodTable()->getCallData(cell, callData) != CallTypeNone;
}

std::unique_ptr<PolyProtoAccessChain> PolyProtoAccessChain::create(JSGlobalObject* globalObject, JSCell* base, JSObject* target, bool& usesPolyProto)
{
    JSCell* current = base;
    VM& vm = *base->vm();

    bool found = false;

    usesPolyProto = false;

    std::unique_ptr<PolyProtoAccessChain> result(new PolyProtoAccessChain());

    for (unsigned iterationNumber = 0; true; ++iterationNumber) {
        Structure* structure = current->structure(vm);

        if (!structure->propertyAccessesAreCacheable())
            return nullptr;

        if (structure->isProxy())
            return nullptr;

        if (structure->isDictionary()) {
            ASSERT(structure->isObject());
            if (structure->hasBeenFlattenedBefore())
                return nullptr;

            structure->flattenDictionaryStructure(vm, asObject(current));
        }

        // To save memory, we don't include the base in the chain. We let
        // AccessCase provide the base to us as needed.
        if (iterationNumber)
            result->m_chain.append(structure);
        else
            RELEASE_ASSERT(current == base);

        if (current == target) {
            found = true;
            break;
        }

        // We only have poly proto if we need to access our prototype via
        // the poly proto protocol. If the slot base is the only poly proto
        // thing in the chain, and we have a cache hit on it, then we're not
        // poly proto.
        usesPolyProto |= structure->hasPolyProto();

        JSValue prototype = structure->prototypeForLookup(globalObject, current);
        if (prototype.isNull())
            break;
        current = asObject(prototype);
    }

    if (!found && !!target)
        return nullptr;

    return result;
}

bool JSObjectIsFunction(JSContextRef ctx, JSObjectRef object)
{
    if (!object)
        return false;
    JSLockHolder locker(toJS(ctx));
    CallData callData;
    JSCell* cell = toJS(object);
    return cell->methodTable()->getCallData(cell, callData) != CallType::None;
}

void SamplingProfiler::processUnverifiedStackTraces()
{
    // This function needs to be called from the JSC execution thread.
    RELEASE_ASSERT(m_lock.isLocked());

    TinyBloomFilter filter = m_vm.heap.objectSpace().blocks().filter();
    MarkedBlockSet& markedBlockSet = m_vm.heap.objectSpace().blocks();

    for (unsigned i = m_indexOfNextStackTraceToVerify; i < m_stackTraces.size(); i++) {
        StackTrace& stackTrace = m_stackTraces[i]; 
        if (!stackTrace.needsVerification)
            continue;
        stackTrace.needsVerification = false;

        for (StackFrame& stackFrame : stackTrace.frames) {
            if (stackFrame.frameType != FrameType::UnverifiedCallee) {
                RELEASE_ASSERT(stackFrame.frameType == FrameType::VerifiedExecutable);
                continue;
            }

            JSValue callee = JSValue::decode(stackFrame.u.unverifiedCallee);
            if (!Heap::isValueGCObject(filter, markedBlockSet, callee)) {
                stackFrame.frameType = FrameType::Unknown;
                continue;
            }

            JSCell* calleeCell = callee.asCell();
            auto frameTypeFromCallData = [&] () -> FrameType {
                FrameType result = FrameType::Unknown;
                CallData callData;
                CallType callType;
                callType = getCallData(calleeCell, callData);
                if (callType == CallTypeHost)
                    result = FrameType::Host;

                return result;
            };

            if (calleeCell->type() != JSFunctionType) {
                stackFrame.frameType = frameTypeFromCallData();
                continue;
            }
            ExecutableBase* executable = static_cast<JSFunction*>(calleeCell)->executable();
            if (!executable) {
                stackFrame.frameType = frameTypeFromCallData();
                continue;
            }

            RELEASE_ASSERT(Heap::isPointerGCObject(filter, markedBlockSet, executable));
            stackFrame.frameType = FrameType::VerifiedExecutable;
            stackFrame.u.verifiedExecutable = executable;
            m_seenExecutables.add(executable);
        }
    }

    m_indexOfNextStackTraceToVerify = m_stackTraces.size();
}

bool JSObjectIsFunction(JSContextRef ctx, JSObjectRef object)
{
    if (!object)
        return false;
    ExecState* exec = toJS(ctx);
    VM& vm = exec->vm();
    JSLockHolder locker(vm);
    CallData callData;
    JSCell* cell = toJS(object);
    return cell->methodTable(vm)->getCallData(cell, callData) != CallType::None;
}

void JSGlobalData::storeVPtrs()
{
    CollectorCell cell;
    void* storage = &cell;

    COMPILE_ASSERT(sizeof(JSArray) <= sizeof(CollectorCell), sizeof_JSArray_must_be_less_than_CollectorCell);
    JSCell* jsArray = new (storage) JSArray(JSArray::createStructure(jsNull()));
    JSGlobalData::jsArrayVPtr = jsArray->vptr();
    jsArray->~JSCell();

    COMPILE_ASSERT(sizeof(JSByteArray) <= sizeof(CollectorCell), sizeof_JSByteArray_must_be_less_than_CollectorCell);
    JSCell* jsByteArray = new (storage) JSByteArray(JSByteArray::VPtrStealingHack);
    JSGlobalData::jsByteArrayVPtr = jsByteArray->vptr();
    jsByteArray->~JSCell();

    COMPILE_ASSERT(sizeof(JSString) <= sizeof(CollectorCell), sizeof_JSString_must_be_less_than_CollectorCell);
    JSCell* jsString = new (storage) JSString(JSString::VPtrStealingHack);
    JSGlobalData::jsStringVPtr = jsString->vptr();
    jsString->~JSCell();

    COMPILE_ASSERT(sizeof(JSFunction) <= sizeof(CollectorCell), sizeof_JSFunction_must_be_less_than_CollectorCell);
    JSCell* jsFunction = new (storage) JSFunction(JSFunction::createStructure(jsNull()));
    JSGlobalData::jsFunctionVPtr = jsFunction->vptr();
    jsFunction->~JSCell();
}

void JSGlobalData::storeVPtrs()
{
    // Enough storage to fit a JSArray, JSByteArray, JSString, or JSFunction.
    // COMPILE_ASSERTS below check that this is true.
    char storage[64];

    COMPILE_ASSERT(sizeof(JSArray) <= sizeof(storage), sizeof_JSArray_must_be_less_than_storage);
    JSCell* jsArray = new (storage) JSArray(JSArray::VPtrStealingHack);
    JSGlobalData::jsArrayVPtr = jsArray->vptr();
    jsArray->~JSCell();

    COMPILE_ASSERT(sizeof(JSByteArray) <= sizeof(storage), sizeof_JSByteArray_must_be_less_than_storage);
    JSCell* jsByteArray = new (storage) JSByteArray(JSByteArray::VPtrStealingHack);
    JSGlobalData::jsByteArrayVPtr = jsByteArray->vptr();
    jsByteArray->~JSCell();

    COMPILE_ASSERT(sizeof(JSString) <= sizeof(storage), sizeof_JSString_must_be_less_than_storage);
    JSCell* jsString = new (storage) JSString(JSString::VPtrStealingHack);
    JSGlobalData::jsStringVPtr = jsString->vptr();
    jsString->~JSCell();

    COMPILE_ASSERT(sizeof(JSFunction) <= sizeof(storage), sizeof_JSFunction_must_be_less_than_storage);
    char executableStorage[sizeof(VPtrHackExecutable)];
    RefPtr<Structure> executableStructure = Structure::create(Structure::VPtrStealingHack, 0);
    JSCell* executable = new (executableStorage) VPtrHackExecutable(executableStructure.get());
    JSCell* jsFunction = new (storage) JSFunction(Structure::create(Structure::VPtrStealingHack, &JSFunction::s_info), static_cast<VPtrHackExecutable*>(executable));
    JSGlobalData::jsFunctionVPtr = jsFunction->vptr();
    executable->~JSCell();
    jsFunction->~JSCell();
}

void JSGlobalData::storeVPtrs()
{
    // Enough storage to fit a JSArray, JSByteArray, JSString, or JSFunction.
    // COMPILE_ASSERTS below check that this is true.
	
	// -----------Instrumentation----------- //
    char storage[128]; // changed from 64 to fit JSLabel
	// ------------------------------------- //

    COMPILE_ASSERT(sizeof(JSArray) <= sizeof(storage), sizeof_JSArray_must_be_less_than_storage);
    JSCell* jsArray = new (storage) JSArray(JSArray::VPtrStealingHack);
    CLOBBER_MEMORY();
    JSGlobalData::jsArrayVPtr = jsArray->vptr();

    COMPILE_ASSERT(sizeof(JSByteArray) <= sizeof(storage), sizeof_JSByteArray_must_be_less_than_storage);
    JSCell* jsByteArray = new (storage) JSByteArray(JSByteArray::VPtrStealingHack);
    CLOBBER_MEMORY();
    JSGlobalData::jsByteArrayVPtr = jsByteArray->vptr();

    COMPILE_ASSERT(sizeof(JSString) <= sizeof(storage), sizeof_JSString_must_be_less_than_storage);
    JSCell* jsString = new (storage) JSString(JSString::VPtrStealingHack);
    CLOBBER_MEMORY();
    JSGlobalData::jsStringVPtr = jsString->vptr();

    COMPILE_ASSERT(sizeof(JSFunction) <= sizeof(storage), sizeof_JSFunction_must_be_less_than_storage);
    JSCell* jsFunction = new (storage) JSFunction(JSCell::VPtrStealingHack);
    CLOBBER_MEMORY();
    JSGlobalData::jsFunctionVPtr = jsFunction->vptr();
}