third_party/WebKit/Source/core/dom/custom/V0CustomElementProcessingStack.h

/*
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 *    may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
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#ifndef V0CustomElementProcessingStack_h
#define V0CustomElementProcessingStack_h

#include "core/CoreExport.h"
#include "core/dom/custom/V0CustomElementCallbackQueue.h"
#include "wtf/Vector.h"

namespace blink {

class CORE_EXPORT V0CustomElementProcessingStack : public GarbageCollectedFinalized<V0CustomElementProcessingStack> {
    WTF_MAKE_NONCOPYABLE(V0CustomElementProcessingStack);
public:
    // This is stack allocated in many DOM callbacks. Make it cheap.
    class CallbackDeliveryScope {
        STACK_ALLOCATED();
    public:
        CallbackDeliveryScope()
            : m_savedElementQueueStart(s_elementQueueStart)
        {
            s_elementQueueStart = s_elementQueueEnd;
        }

        ~CallbackDeliveryScope()
        {
            if (s_elementQueueStart != s_elementQueueEnd)
                processElementQueueAndPop();
            s_elementQueueStart = m_savedElementQueueStart;
        }

    private:
        size_t m_savedElementQueueStart;
    };

    static bool inCallbackDeliveryScope() { return s_elementQueueStart; }

    static V0CustomElementProcessingStack& instance();
    void enqueue(V0CustomElementCallbackQueue*);

    DECLARE_TRACE();

private:
    V0CustomElementProcessingStack()
    {
        // Add a null element as a sentinel. This makes it possible to
        // identify elements queued when there is no
        // CallbackDeliveryScope active. Also, if the processing stack
        // is popped when empty, this sentinel will cause a null deref
        // crash.
        V0CustomElementCallbackQueue* sentinel = 0;
        for (size_t i = 0; i < kNumSentinels; i++)
            m_flattenedProcessingStack.append(sentinel);
        DCHECK_EQ(s_elementQueueEnd, m_flattenedProcessingStack.size());
    }

    // The start of the element queue on the top of the processing
    // stack. An offset into instance().m_flattenedProcessingStack.
    static size_t s_elementQueueStart;

    // The end of the element queue on the top of the processing
    // stack. A cache of instance().m_flattenedProcessingStack.size().
    static size_t s_elementQueueEnd;

    static V0CustomElementCallbackQueue::ElementQueueId currentElementQueue() { return V0CustomElementCallbackQueue::ElementQueueId(s_elementQueueStart); }

    static void processElementQueueAndPop();
    void processElementQueueAndPop(size_t start, size_t end);

    // The processing stack, flattened. Element queues lower in the
    // stack appear toward the head of the vector. The first element
    // is a null sentinel value.
    static const size_t kNumSentinels = 1;
    HeapVector<Member<V0CustomElementCallbackQueue>> m_flattenedProcessingStack;
};

} // namespace blink

#endif // V0CustomElementProcessingStack_h