third_party/blink/renderer/core/execution_context/pausable_object.h

/*
 * Copyright (C) 2008 Apple Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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 */

#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_EXECUTION_CONTEXT_PAUSABLE_OBJECT_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_EXECUTION_CONTEXT_PAUSABLE_OBJECT_H_

#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/core/dom/context_lifecycle_observer.h"
#include "third_party/blink/renderer/platform/wtf/assertions.h"

namespace blink {

// A PausableObject responds to situations where Blink is running a nested event
// loop. At such times, the page should be responsive, but only in a limited
// sense: the browser should redraw the page as necessary, but should not run
// timer callbacks, finish promise resolution, fire events, or perform other
// activity, especially activity which may run script.
//
// Pausing can happen in cases such as:
// - modal dialogs during script execution (e.g. window.alert, window.print)
// - script execution stopped at a debugger breakpoint
//
// The scheduler will automatically suspend certain task queues for the duration
// that the page is paused.
//
// Objects with asynchronous activity, especially activity that may have an
// observable effect on web-visible state, on should suspend that activity while
// the page is paused by overriding ContextPaused() and ContextUnpaused().
//
// https://html.spec.whatwg.org/multipage/webappapis.html#pause
class CORE_EXPORT PausableObject : public ContextLifecycleObserver {
 public:
  explicit PausableObject(ExecutionContext*);

  // PauseIfNeeded() should be called exactly once after object construction
  // to synchronize the suspend state with that in ExecutionContext.
  void PauseIfNeeded();
#if DCHECK_IS_ON()
  bool PauseIfNeededCalled() const { return pause_if_needed_called_; }
#endif

  // These methods have an empty default implementation so that subclasses
  // which don't need special treatment can skip implementation.
  virtual void ContextPaused(PauseState);
  virtual void ContextUnpaused();

  void DidMoveToNewExecutionContext(ExecutionContext*);

 protected:
  virtual ~PausableObject();

 private:
#if DCHECK_IS_ON()
  bool pause_if_needed_called_;
#endif
};

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_EXECUTION_CONTEXT_PAUSABLE_OBJECT_H_