chromium/third_party/blink/renderer/modules/webcodecs/video_frame_monitor.h

// Copyright 2021 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_MODULES_WEBCODECS_VIDEO_FRAME_MONITOR_H_
#define THIRD_PARTY_BLINK_RENDERER_MODULES_WEBCODECS_VIDEO_FRAME_MONITOR_H_

#include <map>
#include <optional>
#include <string>

#include "base/synchronization/lock.h"
#include "media/base/video_frame.h"
#include "third_party/blink/renderer/modules/modules_export.h"
#include "third_party/blink/renderer/platform/allow_discouraged_type.h"
#include "third_party/blink/renderer/platform/wtf/hash_map.h"
#include "third_party/blink/renderer/platform/wtf/hash_traits.h"

namespace blink {

// This class helps monitor usage of media::VideoFrame objects. This class does
// not directly use VideoFrames, but references them using the ID returned by
// media::VideoFrame::unique_id.
// This class is an alternative to using media::VideoFrame destruction observers
// for cases that require monitoring to stop well before the media::VideoFrame
// is destroyed. For example, monitoring blink::VideoFrames backed by
// media::VideoFrames, where the JS-exposed blink::VideoFrames can be closed
// but the backing media::VideoFrames can continue to live outside the
// blink::VideoFrames.
// This class is a per-renderer-process singleton and relies on the fact
// that VideoFrame IDs are unique per process. That means that the same ID
// identifies the same frame regardless of the execution context.
// The motivating use case for this class is keeping track of frames coming
// from sources that have global limits in the number of in-flight frames
// allowed. Thus, frames are monitored per source. Sources are identified with
// a nonempty std::string, so any way to group frames can be used as long as a
// source ID is given. std::string is chosen over the Blink-standard WTF::String
// because:
//   1. source IDs often come from outside Blink (e.g., camera and screen
//      device IDs)
//   2. std::string is easier to use in a multithreaded environment.
// All the methods of this class can be called from any thread.
class MODULES_EXPORT VideoFrameMonitor { … };

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_MODULES_WEBCODECS_VIDEO_FRAME_MONITOR_H_