third_party/WebKit/Source/platform/WebFrameScheduler.h

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef WebFrameScheduler_h
#define WebFrameScheduler_h

#include "platform/wtf/RefPtr.h"
#include "public/platform/TaskType.h"

#include <memory>

namespace blink {

class WebTaskRunner;
class WebViewScheduler;

class WebFrameScheduler {
 public:
  virtual ~WebFrameScheduler() {}

  // Observer type that regulates conditions to invoke callbacks.
  enum class ObserverType { kLoader };

  // Represents throttling state.
  enum class ThrottlingState {
    kThrottled,
    kNotThrottled,
    kStopped,
  };

  // Represents the type of frame: main (top-level) vs not.
  enum class FrameType {
    kMainFrame,
    kSubframe,
  };

  class ActiveConnectionHandle {
   public:
    ActiveConnectionHandle() {}
    virtual ~ActiveConnectionHandle() {}

   private:
    DISALLOW_COPY_AND_ASSIGN(ActiveConnectionHandle);
  };

  // Observer interface to receive scheduling policy change events.
  class Observer {
   public:
    // Notified when throttling state is changed.
    virtual void OnThrottlingStateChanged(ThrottlingState) = 0;
  };

  // Adds an Observer instance to be notified on scheduling policy changed.
  // When an Observer is added, the initial state will be notified synchronously
  // through the Observer interface.
  virtual void AddThrottlingObserver(ObserverType, Observer*) = 0;

  // Removes an Observer instance.
  virtual void RemoveThrottlingObserver(ObserverType, Observer*) = 0;

  // The scheduler may throttle tasks associated with offscreen frames.
  virtual void SetFrameVisible(bool) = 0;
  virtual bool IsFrameVisible() const = 0;

  // Tells the scheduler that the page this frame belongs to is not visible.
  // The scheduler may throttle tasks associated with pages that are not
  // visible.
  virtual void SetPageVisible(bool) = 0;
  virtual bool IsPageVisible() const = 0;

  // Set whether this frame is suspended. Only unthrottledTaskRunner tasks are
  // allowed to run on a suspended frame.
  virtual void SetPaused(bool) = 0;

  // Notifies observers of transitioning to and from STOPPED state in
  // background.
  virtual void SetPageStopped(bool) {}

  // Set whether this frame is cross origin w.r.t. the top level frame. Cross
  // origin frames may use a different scheduling policy from same origin
  // frames.
  virtual void SetCrossOrigin(bool) = 0;
  virtual bool IsCrossOrigin() const = 0;

  // Returns the frame type, which currently determines whether this frame is
  // the top level frame, i.e. a main frame.
  virtual FrameType GetFrameType() const = 0;

  // The tasks runners below are listed in increasing QoS order.
  // - throttleable task queue. Designed for custom user-provided javascript
  //   tasks. Lowest guarantees. Can be paused, blocked during user gesture,
  //   throttled when backgrounded or stopped completely after some time in
  //   background.
  // - deferrable task queue. These tasks can be deferred for a small period
  //   (several seconds) when high-priority work is anticipated. These tasks
  //   can be paused.
  // - pausable task queue. Default queue for high-priority javascript tasks.
  //   They can be paused according to the spec during javascript alert
  //   dialogs, printing windows and devtools debugging. Otherwise scheduler
  //   does not tamper with their execution.
  // - unpausable task queue. Should be used for control tasks which should
  //   run when the context is paused. Usage should be extremely rare.
  //   Please consult scheduler-dev@ before using it. Running javascript
  //   on it is strictly verboten and can lead to hard-to-diagnose errors.
  //
  //
  // These queues below are separate due to special handling for their
  // priorities.
  // - loading task queue. Similar to deferrable task queue. Throttling might
  //   be considered in the future.
  // - loading control task queue. Loading task queue with increased priority
  //   to run small loading tasks which schedule other loading tasks.

  // Note: old-style timer task runner corresponds to throttleable task runner
  // and unthrottled task runner corresponds to pausable task runner.

  // Returns a WebTaskRunner that is suitable with the given task type.
  virtual RefPtr<WebTaskRunner> GetTaskRunner(TaskType) = 0;

  // Returns the parent WebViewScheduler.
  virtual WebViewScheduler* GetWebViewScheduler() = 0;

  // Tells the scheduler a resource load has started. The scheduler may make
  // policy decisions based on this.
  virtual void DidStartLoading(unsigned long identifier) = 0;

  // Tells the scheduler a resource load has stopped. The scheduler may make
  // policy decisions based on this.
  virtual void DidStopLoading(unsigned long identifier) = 0;

  // Tells the scheduler that a history navigation is expected soon, virtual
  // time may be paused. Must be called from the main thread.
  virtual void WillNavigateBackForwardSoon() = 0;

  // Tells the scheduler that a provisional load has started, virtual time may
  // be paused. Must be called from the main thread.
  virtual void DidStartProvisionalLoad(bool is_main_frame) = 0;

  // Tells the scheduler that a provisional load has failed, virtual time may be
  // unpaused. Must be called from the main thread.
  virtual void DidFailProvisionalLoad() = 0;

  // Tells the scheduler that a provisional load has committed, virtual time ma
  // be unpaused. In addition the scheduler may reset the task cost estimators
  // and the UserModel. Must be called from the main thread.
  virtual void DidCommitProvisionalLoad(bool is_web_history_inert_commit,
                                        bool is_reload,
                                        bool is_main_frame) = 0;

  // Tells the scheduler if we are parsing a document on another thread. This
  // tells the scheduler not to advance virtual time if it's using the
  // DETERMINISTIC_LOADING policy.
  virtual void SetDocumentParsingInBackground(
      bool background_parsing_enabled) = 0;

  // Tells the scheduler that the first meaningful paint has occured for this
  // frame.
  virtual void OnFirstMeaningfulPaint() = 0;

  // Notifies scheduler that this frame has established an active real time
  // connection (websocket, webrtc, etc). When connection is closed this handle
  // must be destroyed.
  virtual std::unique_ptr<ActiveConnectionHandle>
  OnActiveConnectionCreated() = 0;

  // Returns true if this frame is should not throttled (e.g. because of audio
  // or an active connection).
  virtual bool IsExemptFromThrottling() const = 0;
};

}  // namespace blink

#endif  // WebFrameScheduler_h