chromium/third_party/blink/renderer/core/paint/timing/paint_timing_callback_manager.h

// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_PAINT_TIMING_PAINT_TIMING_CALLBACK_MANAGER_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_PAINT_TIMING_PAINT_TIMING_CALLBACK_MANAGER_H_

#include <queue>

#include "base/functional/callback_forward.h"
#include "base/time/time.h"
#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/core/frame/local_frame_view.h"
#include "third_party/blink/renderer/platform/heap/garbage_collected.h"

namespace viz {
struct FrameTimingDetails;
}

namespace blink {

// `PaintTimingCallbackManager` is an interface between
// `ImagePaintTimingDetector`/`TextPaintTimingDetector` and `ChromeClient`.
// As `ChromeClient` is shared among the paint-timing-detectors, it
// makes it hard to test each detector without being affected other detectors.
// The interface, however, allows unit tests to mock `ChromeClient` for each
// detector. With the mock, `ImagePaintTimingDetector`'s callback does not need
// to store in the same queue as `TextPaintTimingDetector`'s. The separate
// queue makes it possible to pop an `ImagePaintTimingDetector`'s callback
// without having to popping the `TextPaintTimingDetector`'s.
class PaintTimingCallbackManager : public GarbageCollectedMixin { … };

// This class is responsible for managing the swap-time callback for Largest
// Image Paint and Largest Text Paint. In frames where both text and image are
// painted, Largest Image Paint and Largest Text Paint need to assign the same
// paint-time for their records. In this case, `PaintTimeCallbackManager`
// requests a swap-time callback and share the swap-time with LIP and LTP.
// Otherwise LIP and LTP would have to request their own swap-time callbacks.
// An extra benefit of this design is that `LargestContentfulPaintCalculator`
// can thus hook to the end of the LIP and LTP's record assignments.
//
// `GarbageCollected` inheritance is required by the swap-time callback
// registration.
class CORE_EXPORT PaintTimingCallbackManagerImpl final
    : public GarbageCollected<PaintTimingCallbackManagerImpl>,
      public PaintTimingCallbackManager { … };
}  // namespace blink
#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_PAINT_TIMING_PAINT_TIMING_CALLBACK_MANAGER_H_