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* Copyright 2023 The WebRTC Project Authors. All rights reserved.
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
// This header file provides wrapper for common WebRTC utilities.
// Different application may need different implementations of these utilities,
// Moreover, single application may need to use WebRTC for multiple purposes,
// and thus would need to provide different utilities implementations for
// different peer connections.
// The main purpose of the `Environment` class below is to propagate references
// to those utilities to all WebRTC classes that need them.
#include <utility>
#include "absl/base/nullability.h"
#include "api/ref_counted_base.h"
#include "api/scoped_refptr.h"
#include "rtc_base/system/rtc_export.h"
namespace webrtc {
// These classes are forward declared to keep Environment dependencies
// lightweight. Users who need any of the types below should include their
// header explicitely.
class Clock;
class TaskQueueFactory;
class FieldTrialsView;
class RtcEventLog;
// Contains references to WebRTC utilities. Object of this class should be
// passed as a construction parameter and saved by value in each class that
// needs it. Most classes shouldn't create a new instance of the `Environment`,
// but instead should use a propagated copy.
// Usually Environment should be the first parameter in a constructor or a
// factory, and the first member in the class. Keeping Environment as the first
// member in the class ensures utilities (e.g. clock) are still valid during
// destruction of other members.
// Example:
// class PeerConnection {
// public:
// PeerConnection(const Environment& env, ...)
// : env_(env),
// log_duration_on_destruction_(&env_.clock()),
// rtp_manager_(env_, ...),
// ...
// const FieldTrialsView& trials() const { return env_.field_trials(); }
// scoped_refptr<RtpTransceiverInterface> AddTransceiver(...) {
// return make_ref_counted<RtpTransceiverImpl>(env_, ...);
// }
// private:
// const Environment env_;
// Stats log_duration_on_destruction_;
// RtpTransmissionManager rtp_manager_;
// };
// This class is thread safe.
class RTC_EXPORT Environment final {
// Default constructor is deleted in favor of creating this object using
// `EnvironmentFactory`. To create the default environment use
// `EnvironmentFactory().Create()` or `CreateEnvironment()`.
Environment() = delete;
Environment(const Environment&) = default;
Environment(Environment&&) = default;
Environment& operator=(const Environment&) = default;
Environment& operator=(Environment&&) = default;
~Environment() = default;
// Provides means to alter behavior, mostly for A/B testing new features.
// See ../../g3doc/
const FieldTrialsView& field_trials() const;
// Provides an interface to query current time.
// See ../../g3doc/
Clock& clock() const;
// Provides a factory for task queues, WebRTC threading primitives.
// See ../../g3doc/
TaskQueueFactory& task_queue_factory() const;
// Provides an interface for collecting structured logs.
// See ../../logging/g3doc/
RtcEventLog& event_log() const;
friend class EnvironmentFactory;
Environment(scoped_refptr<const rtc::RefCountedBase> storage,
absl::Nonnull<const FieldTrialsView*> field_trials,
absl::Nonnull<Clock*> clock,
absl::Nonnull<TaskQueueFactory*> task_queue_factory,
absl::Nonnull<RtcEventLog*> event_log)
: storage_(std::move(storage)),
event_log_(event_log) {}
// Container that keeps ownership of the utilities below.
// Defining this as a RefCountedBase allows `Environment` to share this
// storage with another `Environment`, in particular allows `Environment` to
// be copyable. It is up to the `EnvironmentFactory` to provide an object that
// ensures references to utilties below are valid while object in the
// `storage_` is alive.
scoped_refptr<const rtc::RefCountedBase> storage_;
absl::Nonnull<const FieldTrialsView*> field_trials_;
absl::Nonnull<Clock*> clock_;
absl::Nonnull<TaskQueueFactory*> task_queue_factory_;
absl::Nonnull<RtcEventLog*> event_log_;
// Implementation details follow
inline const FieldTrialsView& Environment::field_trials() const {
return *field_trials_;
inline Clock& Environment::clock() const {
return *clock_;
inline TaskQueueFactory& Environment::task_queue_factory() const {
return *task_queue_factory_;
inline RtcEventLog& Environment::event_log() const {
return *event_log_;
} // namespace webrtc