third_party/blink/renderer/core/html/custom/v0_custom_element_processing_stack.h

/*
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 * modification, are permitted provided that the following conditions
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 * 1. Redistributions of source code must retain the above copyright
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 *    in the documentation and/or other materials provided with the
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 *    may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_HTML_CUSTOM_V0_CUSTOM_ELEMENT_PROCESSING_STACK_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_HTML_CUSTOM_V0_CUSTOM_ELEMENT_PROCESSING_STACK_H_

#include "base/macros.h"
#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/core/html/custom/v0_custom_element_callback_queue.h"
#include "third_party/blink/renderer/platform/wtf/vector.h"

namespace blink {

class CORE_EXPORT V0CustomElementProcessingStack
    : public GarbageCollected<V0CustomElementProcessingStack> {
 public:
  // This is stack allocated in many DOM callbacks. Make it cheap.
  class CallbackDeliveryScope {
    STACK_ALLOCATED();

   public:
    CallbackDeliveryScope() : saved_element_queue_start_(element_queue_start_) {
      element_queue_start_ = element_queue_end_;
    }

    ~CallbackDeliveryScope() {
      if (element_queue_start_ != element_queue_end_)
        ProcessElementQueueAndPop();
      element_queue_start_ = saved_element_queue_start_;
    }

   private:
    wtf_size_t saved_element_queue_start_;
  };

  static bool InCallbackDeliveryScope() { return element_queue_start_; }

  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 = nullptr;
    for (wtf_size_t i = 0; i < kNumSentinels; i++)
      flattened_processing_stack_.push_back(sentinel);
    DCHECK_EQ(element_queue_end_, flattened_processing_stack_.size());
  }

  static V0CustomElementProcessingStack& Instance();
  void Enqueue(V0CustomElementCallbackQueue*);

  void Trace(blink::Visitor*);

 private:
  // The start of the element queue on the top of the processing
  // stack. An offset into Instance().flattened_processing_stack_.
  static wtf_size_t element_queue_start_;

  // The end of the element queue on the top of the processing
  // stack. A cache of Instance().flattened_processing_stack_.size().
  static wtf_size_t element_queue_end_;

  static V0CustomElementCallbackQueue::ElementQueueId CurrentElementQueue() {
    return V0CustomElementCallbackQueue::ElementQueueId(element_queue_start_);
  }

  static void ProcessElementQueueAndPop();
  void ProcessElementQueueAndPop(wtf_size_t start, wtf_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 wtf_size_t kNumSentinels = 1;
  HeapVector<Member<V0CustomElementCallbackQueue>> flattened_processing_stack_;

  DISALLOW_COPY_AND_ASSIGN(V0CustomElementProcessingStack);
};

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_HTML_CUSTOM_V0_CUSTOM_ELEMENT_PROCESSING_STACK_H_