Reland "[DataChannel] Send and receive packets on the network thread."
This reverts commit 7f16fcda0fd5bb625584b71311dd37b54c096136.
Reason for reland: Re-landing after addressing issues in downstream
code and hardening the ObserverAdapter from situations where attempted
usage of data channel proxies could occur after shutting down the
peer connection and terminating the network thread.
Original change's description:
> Revert "[DataChannel] Send and receive packets on the network thread."
>
> This reverts commit fe53fec24e02d2d644220f913c3f9ae596bbb2d9.
>
> Reason for revert: Speculative revert, may be breaking downstream project
>
> Original change's description:
> > [DataChannel] Send and receive packets on the network thread.
> >
> > This updates sctp channels, including work that happens between the
> > data channel controller and the transport, to run on the network
> > thread. Previously all network traffic related to data channels was
> > routed through the signaling thread before going to either the network
> > thread or the caller's thread (e.g. js thread in chrome). Now the
> > calls can go straight from the network thread to the JS thread with
> > enabling a special flag on the observer (see below) and similarly
> > calls to send data, involve 2 threads instead of 3.
> >
> > * Custom data channel observer adapter implementation that
> > maintains compatibility with existing observer implementations in
> > that notifications are delivered on the signaling thread.
> > The adapter can be explicitly disabled for implementations that
> > want to optimize the callback path and promise to not block the
> > network thread.
> > * Remove the signaling thread copy of data channels in the controller.
> > * Remove several PostTask operations that were needed to keep things
> > in sync (but the need has gone away).
> > * Update tests for the controller to consistently call
> > TeardownDataChannelTransport_n to match with production.
> > * Update stats collectors (current and legacy) to fetch the data
> > channel stats on the network thread where they're maintained.
> > * Remove the AsyncChannelCloseTeardown test since the async teardown
> > step has gone away.
> > * Remove `sid_s` in the channel code since we only need the network
> > state now.
> > * For the custom observer support (with and without data adapter) and
> > maintain compatibility with existing implementations, added a new
> > proxy macro that allows an implementation to selectively provide
> > its own implementation without being proxied. This is used for
> > registering/unregistering a data channel observer.
> > * Update the data channel proxy to map most methods to the network
> > thread, avoiding the interim jump to the signaling thread.
> > * Update a plethora of thread checkers from signaling to network.
> >
> > Bug: webrtc:11547
> > Change-Id: Ib4cff1482e31c46008e187189a79e967389bc518
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/299142
> > Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
> > Reviewed-by: Henrik Boström <hbos@webrtc.org>
> > Cr-Commit-Position: refs/heads/main@{#39760}
>
> Bug: webrtc:11547
> Change-Id: Id0d65594bf727ccea5c49093c942b09714d101ad
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/300341
> Auto-Submit: Andrey Logvin <landrey@webrtc.org>
> Owners-Override: Andrey Logvin <landrey@webrtc.org>
> Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
> Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#39764}
Bug: webrtc:11547
Change-Id: I47dfa7e7168be0cd2faab4f8f3ebf110c3728af5
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/300360
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39786}
diff --git a/pc/data_channel_controller.cc b/pc/data_channel_controller.cc
index 36e8be1..b1ebfc0 100644
--- a/pc/data_channel_controller.cc
+++ b/pc/data_channel_controller.cc
@@ -29,8 +29,15 @@
}
bool DataChannelController::HasDataChannelsForTest() const {
- RTC_DCHECK_RUN_ON(signaling_thread());
- return !sctp_data_channels_.empty();
+ auto has_channels = [&] {
+ RTC_DCHECK_RUN_ON(network_thread());
+ return !sctp_data_channels_n_.empty();
+ };
+
+ if (network_thread()->IsCurrent())
+ return has_channels();
+
+ return network_thread()->BlockingCall(std::move(has_channels));
}
bool DataChannelController::HasUsedDataChannels() const {
@@ -66,11 +73,15 @@
void DataChannelController::OnChannelStateChanged(
SctpDataChannel* channel,
DataChannelInterface::DataState state) {
- RTC_DCHECK_RUN_ON(signaling_thread());
+ RTC_DCHECK_RUN_ON(network_thread());
if (state == DataChannelInterface::DataState::kClosed)
OnSctpDataChannelClosed(channel);
- pc_->OnSctpDataChannelStateChanged(channel->internal_id(), state);
+ signaling_thread()->PostTask(
+ SafeTask(signaling_safety_.flag(),
+ [this, channel_id = channel->internal_id(), state = state] {
+ pc_->OnSctpDataChannelStateChanged(channel_id, state);
+ }));
}
void DataChannelController::OnDataReceived(
@@ -82,27 +93,22 @@
if (HandleOpenMessage_n(channel_id, type, buffer))
return;
- signaling_thread()->PostTask(
- SafeTask(signaling_safety_.flag(), [this, channel_id, type, buffer] {
- RTC_DCHECK_RUN_ON(signaling_thread());
- // TODO(bugs.webrtc.org/11547): The data being received should be
- // delivered on the network thread.
- auto it = FindChannel(StreamId(channel_id));
- if (it != sctp_data_channels_.end())
- (*it)->OnDataReceived(type, buffer);
- }));
+ auto it = absl::c_find_if(sctp_data_channels_n_, [&](const auto& c) {
+ return c->sid_n().stream_id_int() == channel_id;
+ });
+
+ if (it != sctp_data_channels_n_.end())
+ (*it)->OnDataReceived(type, buffer);
}
void DataChannelController::OnChannelClosing(int channel_id) {
RTC_DCHECK_RUN_ON(network_thread());
- signaling_thread()->PostTask(
- SafeTask(signaling_safety_.flag(), [this, channel_id] {
- RTC_DCHECK_RUN_ON(signaling_thread());
- // TODO(bugs.webrtc.org/11547): Should run on the network thread.
- auto it = FindChannel(StreamId(channel_id));
- if (it != sctp_data_channels_.end())
- (*it)->OnClosingProcedureStartedRemotely();
- }));
+ auto it = absl::c_find_if(sctp_data_channels_n_, [&](const auto& c) {
+ return c->sid_n().stream_id_int() == channel_id;
+ });
+
+ if (it != sctp_data_channels_n_.end())
+ (*it)->OnClosingProcedureStartedRemotely();
}
void DataChannelController::OnChannelClosed(int channel_id) {
@@ -112,48 +118,44 @@
auto it = absl::c_find_if(sctp_data_channels_n_,
[&](const auto& c) { return c->sid_n() == sid; });
- if (it != sctp_data_channels_n_.end())
+ if (it != sctp_data_channels_n_.end()) {
+ rtc::scoped_refptr<SctpDataChannel> channel = std::move(*it);
sctp_data_channels_n_.erase(it);
-
- signaling_thread()->PostTask(SafeTask(signaling_safety_.flag(), [this, sid] {
- RTC_DCHECK_RUN_ON(signaling_thread());
- auto it = FindChannel(sid);
- // Remove the channel from our list, close it and free up resources.
- if (it != sctp_data_channels_.end()) {
- rtc::scoped_refptr<SctpDataChannel> channel = std::move(*it);
- // Note: this causes OnSctpDataChannelClosed() to not do anything
- // when called from within `OnClosingProcedureComplete`.
- sctp_data_channels_.erase(it);
-
- channel->OnClosingProcedureComplete();
- }
- }));
+ channel->OnClosingProcedureComplete();
+ }
}
void DataChannelController::OnReadyToSend() {
RTC_DCHECK_RUN_ON(network_thread());
- signaling_thread()->PostTask(SafeTask(signaling_safety_.flag(), [this] {
- RTC_DCHECK_RUN_ON(signaling_thread());
- auto copy = sctp_data_channels_;
- for (const auto& channel : copy)
+ auto copy = sctp_data_channels_n_;
+ for (const auto& channel : copy) {
+ if (channel->sid_n().HasValue()) {
channel->OnTransportReady();
- }));
+ } else {
+ // This happens for role==SSL_SERVER channels when we get notified by
+ // the transport *before* the SDP code calls `AllocateSctpSids` to
+ // trigger assignment of sids. In this case OnTransportReady() will be
+ // called from within `AllocateSctpSids` below.
+ RTC_LOG(LS_INFO) << "OnReadyToSend: Still waiting for an id for channel.";
+ }
+ }
}
void DataChannelController::OnTransportClosed(RTCError error) {
RTC_DCHECK_RUN_ON(network_thread());
- signaling_thread()->PostTask(
- SafeTask(signaling_safety_.flag(), [this, error] {
- RTC_DCHECK_RUN_ON(signaling_thread());
- OnTransportChannelClosed(error);
- }));
+ // This loop will close all data channels and trigger a callback to
+ // `OnSctpDataChannelClosed` which will modify `sctp_data_channels_n_`, so
+ // we create a local copy while we do the fan-out.
+ auto copy = sctp_data_channels_n_;
+ for (const auto& channel : copy)
+ channel->OnTransportChannelClosed(error);
}
void DataChannelController::SetupDataChannelTransport_n() {
RTC_DCHECK_RUN_ON(network_thread());
// There's a new data channel transport. This needs to be signaled to the
- // `sctp_data_channels_` so that they can reopen and reconnect. This is
+ // `sctp_data_channels_n_` so that they can reopen and reconnect. This is
// necessary when bundling is applied.
NotifyDataChannelsOfTransportCreated();
}
@@ -165,11 +167,12 @@
void DataChannelController::TeardownDataChannelTransport_n() {
RTC_DCHECK_RUN_ON(network_thread());
- if (data_channel_transport()) {
- data_channel_transport()->SetDataSink(nullptr);
+ if (data_channel_transport_) {
+ data_channel_transport_->SetDataSink(nullptr);
+ set_data_channel_transport(nullptr);
}
- set_data_channel_transport(nullptr);
sctp_data_channels_n_.clear();
+ weak_factory_.InvalidateWeakPtrs();
}
void DataChannelController::OnTransportChanged(
@@ -185,7 +188,7 @@
new_data_channel_transport->SetDataSink(this);
// There's a new data channel transport. This needs to be signaled to the
- // `sctp_data_channels_` so that they can reopen and reconnect. This is
+ // `sctp_data_channels_n_` so that they can reopen and reconnect. This is
// necessary when bundling is applied.
NotifyDataChannelsOfTransportCreated();
}
@@ -194,10 +197,10 @@
std::vector<DataChannelStats> DataChannelController::GetDataChannelStats()
const {
- RTC_DCHECK_RUN_ON(signaling_thread());
+ RTC_DCHECK_RUN_ON(network_thread());
std::vector<DataChannelStats> stats;
- stats.reserve(sctp_data_channels_.size());
- for (const auto& channel : sctp_data_channels_)
+ stats.reserve(sctp_data_channels_n_.size());
+ for (const auto& channel : sctp_data_channels_n_)
stats.push_back(channel->GetStats());
return stats;
}
@@ -219,28 +222,38 @@
<< channel_id;
} else {
config.open_handshake_role = InternalDataChannelInit::kAcker;
- signaling_thread()->PostTask(
- SafeTask(signaling_safety_.flag(),
- [this, label = std::move(label), config = std::move(config)] {
- RTC_DCHECK_RUN_ON(signaling_thread());
- OnDataChannelOpenMessage(label, config);
- }));
+ auto channel_or_error = CreateDataChannel(label, config);
+ if (channel_or_error.ok()) {
+ signaling_thread()->PostTask(SafeTask(
+ signaling_safety_.flag(),
+ [this, channel = channel_or_error.MoveValue(),
+ ready_to_send = data_channel_transport_->IsReadyToSend()] {
+ RTC_DCHECK_RUN_ON(signaling_thread());
+ OnDataChannelOpenMessage(std::move(channel), ready_to_send);
+ }));
+ } else {
+ RTC_LOG(LS_ERROR) << "Failed to create DataChannel from the OPEN message."
+ << ToString(channel_or_error.error().type());
+ }
}
return true;
}
void DataChannelController::OnDataChannelOpenMessage(
- const std::string& label,
- const InternalDataChannelInit& config) {
- auto channel_or_error = InternalCreateDataChannelWithProxy(label, config);
- if (!channel_or_error.ok()) {
- RTC_LOG(LS_ERROR) << "Failed to create DataChannel from the OPEN message."
- << ToString(channel_or_error.error().type());
- return;
- }
+ rtc::scoped_refptr<SctpDataChannel> channel,
+ bool ready_to_send) {
+ has_used_data_channels_ = true;
+ auto proxy = SctpDataChannel::CreateProxy(channel, signaling_safety_.flag());
- pc_->Observer()->OnDataChannel(channel_or_error.MoveValue());
+ pc_->Observer()->OnDataChannel(proxy);
pc_->NoteDataAddedEvent();
+
+ if (ready_to_send) {
+ network_thread()->PostTask([channel = std::move(channel)] {
+ if (channel->state() != DataChannelInterface::DataState::kClosed)
+ channel->OnTransportReady();
+ });
+ }
}
// RTC_RUN_ON(network_thread())
@@ -269,6 +282,31 @@
return RTCError::OK();
}
+// RTC_RUN_ON(network_thread())
+RTCErrorOr<rtc::scoped_refptr<SctpDataChannel>>
+DataChannelController::CreateDataChannel(const std::string& label,
+ InternalDataChannelInit& config) {
+ StreamId sid(config.id);
+ RTCError err = ReserveOrAllocateSid(sid, config.fallback_ssl_role);
+ if (!err.ok())
+ return err;
+
+ // In case `sid` has changed. Update `config` accordingly.
+ config.id = sid.stream_id_int();
+
+ rtc::scoped_refptr<SctpDataChannel> channel = SctpDataChannel::Create(
+ weak_factory_.GetWeakPtr(), label, data_channel_transport_ != nullptr,
+ config, signaling_thread(), network_thread());
+ RTC_DCHECK(channel);
+ sctp_data_channels_n_.push_back(channel);
+
+ // If we have an id already, notify the transport.
+ if (sid.HasValue())
+ AddSctpDataStream(sid);
+
+ return channel;
+}
+
RTCErrorOr<rtc::scoped_refptr<DataChannelInterface>>
DataChannelController::InternalCreateDataChannelWithProxy(
const std::string& label,
@@ -283,29 +321,25 @@
bool ready_to_send = false;
InternalDataChannelInit new_config = config;
StreamId sid(new_config.id);
- auto weak_ptr = weak_factory_.GetWeakPtr();
- RTC_DCHECK(weak_ptr); // Associate with current thread.
auto ret = network_thread()->BlockingCall(
[&]() -> RTCErrorOr<rtc::scoped_refptr<SctpDataChannel>> {
RTC_DCHECK_RUN_ON(network_thread());
- RTCError err = ReserveOrAllocateSid(sid, new_config.fallback_ssl_role);
- if (!err.ok())
- return err;
-
- // In case `sid` has changed. Update `new_config` accordingly.
- new_config.id = sid.stream_id_int();
+ auto channel = CreateDataChannel(label, new_config);
+ if (!channel.ok())
+ return channel;
ready_to_send =
data_channel_transport_ && data_channel_transport_->IsReadyToSend();
-
- rtc::scoped_refptr<SctpDataChannel> channel(SctpDataChannel::Create(
- std::move(weak_ptr), label, data_channel_transport_ != nullptr,
- new_config, signaling_thread(), network_thread()));
- RTC_DCHECK(channel);
- sctp_data_channels_n_.push_back(channel);
-
- // If we have an id already, notify the transport.
- if (sid.HasValue())
- AddSctpDataStream(sid);
+ if (ready_to_send) {
+ // If the transport is ready to send because the initial channel
+ // ready signal may have been sent before the DataChannel creation.
+ // This has to be done async because the upper layer objects (e.g.
+ // Chrome glue and WebKit) are not wired up properly until after
+ // `InternalCreateDataChannelWithProxy` returns.
+ network_thread()->PostTask([channel = channel.value()] {
+ if (channel->state() != DataChannelInterface::DataState::kClosed)
+ channel->OnTransportReady();
+ });
+ }
return channel;
});
@@ -313,114 +347,72 @@
if (!ret.ok())
return ret.MoveError();
- if (ready_to_send) {
- // Checks if the transport is ready to send because the initial channel
- // ready signal may have been sent before the DataChannel creation.
- // This has to be done async because the upper layer objects (e.g.
- // Chrome glue and WebKit) are not wired up properly until after this
- // function returns.
- signaling_thread()->PostTask(
- SafeTask(signaling_safety_.flag(), [channel = ret.value()] {
- if (channel->state() != DataChannelInterface::DataState::kClosed)
- channel->OnTransportReady();
- }));
- }
-
- sctp_data_channels_.push_back(ret.value());
has_used_data_channels_ = true;
- return SctpDataChannel::CreateProxy(ret.MoveValue());
+ return SctpDataChannel::CreateProxy(ret.MoveValue(),
+ signaling_safety_.flag());
}
void DataChannelController::AllocateSctpSids(rtc::SSLRole role) {
- RTC_DCHECK_RUN_ON(signaling_thread());
+ RTC_DCHECK_RUN_ON(network_thread());
+
+ const bool ready_to_send =
+ data_channel_transport_ && data_channel_transport_->IsReadyToSend();
std::vector<std::pair<SctpDataChannel*, StreamId>> channels_to_update;
std::vector<rtc::scoped_refptr<SctpDataChannel>> channels_to_close;
-
- network_thread()->BlockingCall([&] {
- RTC_DCHECK_RUN_ON(network_thread());
- for (auto it = sctp_data_channels_n_.begin();
- it != sctp_data_channels_n_.end();) {
- if (!(*it)->sid_n().HasValue()) {
- StreamId sid = sid_allocator_.AllocateSid(role);
- if (sid.HasValue()) {
- (*it)->SetSctpSid_n(sid);
- AddSctpDataStream(sid);
- channels_to_update.push_back(std::make_pair((*it).get(), sid));
- } else {
- channels_to_close.push_back(std::move(*it));
- it = sctp_data_channels_n_.erase(it);
- continue;
+ for (auto it = sctp_data_channels_n_.begin();
+ it != sctp_data_channels_n_.end();) {
+ if (!(*it)->sid_n().HasValue()) {
+ StreamId sid = sid_allocator_.AllocateSid(role);
+ if (sid.HasValue()) {
+ (*it)->SetSctpSid_n(sid);
+ AddSctpDataStream(sid);
+ if (ready_to_send) {
+ RTC_LOG(LS_INFO) << "AllocateSctpSids: Id assigned, ready to send.";
+ (*it)->OnTransportReady();
}
+ channels_to_update.push_back(std::make_pair((*it).get(), sid));
+ } else {
+ channels_to_close.push_back(std::move(*it));
+ it = sctp_data_channels_n_.erase(it);
+ continue;
}
- ++it;
}
- });
+ ++it;
+ }
// Since closing modifies the list of channels, we have to do the actual
// closing outside the loop.
for (const auto& channel : channels_to_close) {
channel->CloseAbruptlyWithDataChannelFailure("Failed to allocate SCTP SID");
- // The channel should now have been removed from sctp_data_channels_.
- RTC_DCHECK(absl::c_find_if(sctp_data_channels_, [&](const auto& c) {
- return c.get() == channel.get();
- }) == sctp_data_channels_.end());
- }
-
- for (auto& pair : channels_to_update) {
- auto it = absl::c_find_if(sctp_data_channels_, [&](const auto& c) {
- return c.get() == pair.first;
- });
- RTC_DCHECK(it != sctp_data_channels_.end());
- (*it)->SetSctpSid_s(pair.second);
}
}
void DataChannelController::OnSctpDataChannelClosed(SctpDataChannel* channel) {
- RTC_DCHECK_RUN_ON(signaling_thread());
-
- network_thread()->BlockingCall([&] {
- RTC_DCHECK_RUN_ON(network_thread());
- // After the closing procedure is done, it's safe to use this ID for
- // another data channel.
- if (channel->sid_n().HasValue()) {
- sid_allocator_.ReleaseSid(channel->sid_n());
- }
-
- auto it = absl::c_find_if(sctp_data_channels_n_, [&](const auto& c) {
- return c.get() == channel;
- });
-
- if (it != sctp_data_channels_n_.end())
- sctp_data_channels_n_.erase(it);
- });
-
- for (auto it = sctp_data_channels_.begin(); it != sctp_data_channels_.end();
- ++it) {
- if (it->get() == channel) {
- // Since this method is triggered by a signal from the DataChannel,
- // we can't free it directly here; we need to free it asynchronously.
- rtc::scoped_refptr<SctpDataChannel> release = std::move(*it);
- sctp_data_channels_.erase(it);
- signaling_thread()->PostTask(SafeTask(signaling_safety_.flag(),
- [release = std::move(release)] {}));
- return;
- }
+ RTC_DCHECK_RUN_ON(network_thread());
+ // After the closing procedure is done, it's safe to use this ID for
+ // another data channel.
+ if (channel->sid_n().HasValue()) {
+ sid_allocator_.ReleaseSid(channel->sid_n());
}
+ auto it = absl::c_find_if(sctp_data_channels_n_,
+ [&](const auto& c) { return c.get() == channel; });
+ if (it != sctp_data_channels_n_.end())
+ sctp_data_channels_n_.erase(it);
}
void DataChannelController::OnTransportChannelClosed(RTCError error) {
- RTC_DCHECK_RUN_ON(signaling_thread());
+ RTC_DCHECK_RUN_ON(network_thread());
// Use a temporary copy of the SCTP DataChannel list because the
// DataChannel may callback to us and try to modify the list.
// TODO(tommi): `OnTransportChannelClosed` is called from
// `SdpOfferAnswerHandler::DestroyDataChannelTransport` just before
// `TeardownDataChannelTransport_n` is called (but on the network thread) from
- // the same function. Once `sctp_data_channels_` moves to the network thread,
- // we can get rid of this function (OnTransportChannelClosed) and run this
- // loop from within the TeardownDataChannelTransport_n callback.
+ // the same function. We can now get rid of this function
+ // (OnTransportChannelClosed) and run this loop from within the
+ // TeardownDataChannelTransport_n callback.
std::vector<rtc::scoped_refptr<SctpDataChannel>> temp_sctp_dcs;
- temp_sctp_dcs.swap(sctp_data_channels_);
+ temp_sctp_dcs.swap(sctp_data_channels_n_);
for (const auto& channel : temp_sctp_dcs) {
channel->OnTransportChannelClosed(error);
}
@@ -444,16 +436,10 @@
StreamId sid,
const SendDataParams& params,
const rtc::CopyOnWriteBuffer& payload) {
- // TODO(bugs.webrtc.org/11547): Expect method to be called on the network
- // thread instead. Remove the BlockingCall() below and move associated state
- // to the network thread.
- RTC_DCHECK_RUN_ON(signaling_thread());
+ RTC_DCHECK_RUN_ON(network_thread());
RTC_DCHECK(data_channel_transport());
-
- return network_thread()->BlockingCall([this, sid, params, payload] {
- return data_channel_transport()->SendData(sid.stream_id_int(), params,
- payload);
- });
+ return data_channel_transport()->SendData(sid.stream_id_int(), params,
+ payload);
}
void DataChannelController::NotifyDataChannelsOfTransportCreated() {
@@ -463,27 +449,14 @@
for (const auto& channel : sctp_data_channels_n_) {
if (channel->sid_n().HasValue())
AddSctpDataStream(channel->sid_n());
+ channel->OnTransportChannelCreated();
}
-
- signaling_thread()->PostTask(SafeTask(signaling_safety_.flag(), [this] {
- RTC_DCHECK_RUN_ON(signaling_thread());
- for (const auto& channel : sctp_data_channels_) {
- channel->OnTransportChannelCreated();
- }
- }));
-}
-
-std::vector<rtc::scoped_refptr<SctpDataChannel>>::iterator
-DataChannelController::FindChannel(StreamId stream_id) {
- RTC_DCHECK_RUN_ON(signaling_thread());
- return absl::c_find_if(sctp_data_channels_, [&](const auto& c) {
- return c->sid_s() == stream_id;
- });
}
rtc::Thread* DataChannelController::network_thread() const {
return pc_->network_thread();
}
+
rtc::Thread* DataChannelController::signaling_thread() const {
return pc_->signaling_thread();
}
