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Fix potential race in PacketSequencer.

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The race can happen when an encoder thread is packetizing a video frame
and is calling RTPSender::AssignSequenceNumber() while the RtpRtcp
module is calling GeneratePadding() and querying
PacketSequencer::CanSendPaddingOnMediaSsrc().

The solution for now is to simply not call
PacketSequencer::CanSendPaddingOnMediaSsrc() from the RtpRtcp module,
as that parameter will be ignored anyway - RTPSender will query that
method internally while holding the send lock.

Once deferred sequencing is implemented, the
can_send_padding_on_media_ssrc parameter can be populated safely since
it is then always called on the pacer thread.

Bug: webrtc:11340, webrtc:12470
Change-Id: I9e90808166453d0e29746df89044e1d3bdffa286
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227767
Reviewed-by: Tommi <tommi@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34655}
This commit is contained in:
Erik Språng
2021-08-05 16:15:14 +02:00
committed by WebRTC LUCI CQ
parent 35b1cb455f
commit 51e30837d5
2 changed files with 8 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
modules/rtp_rtcp/source/rtp_rtcp_impl2.cc
View File

@ -398,9 +398,12 @@ bool ModuleRtpRtcpImpl2::SupportsRtxPayloadPadding() const {
std::vector<std::unique_ptr<RtpPacketToSend>>
ModuleRtpRtcpImpl2::GeneratePadding(size_t target_size_bytes) {
RTC_DCHECK(rtp_sender_);
// `can_send_padding_on_media_ssrc` set to false but is ignored at this
// point, RTPSender will internally query `sequencer_` while holding the
// send lock.
return rtp_sender_->packet_generator.GeneratePadding(
target_size_bytes, rtp_sender_->packet_sender.MediaHasBeenSent(),
rtp_sender_->sequencer_.CanSendPaddingOnMediaSsrc());
/*can_send_padding_on_media_ssrc=*/false);
}
std::vector<RtpSequenceNumberMap::Info>