Add support for transport wide sequence numbers

webrtc/modules/pacing/packet_router.cc

 /*
  *  Copyright (c) 2015 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.
  */
 
 #include "webrtc/modules/pacing/include/packet_router.h"
 
+#include "webrtc/base/atomicops.h"
 #include "webrtc/base/checks.h"
 #include "webrtc/modules/rtp_rtcp/interface/rtp_rtcp.h"
 #include "webrtc/modules/rtp_rtcp/interface/rtp_rtcp_defines.h"
-#include "webrtc/system_wrappers/interface/critical_section_wrapper.h"
 
 namespace webrtc {
 
-PacketRouter::PacketRouter()
-    : crit_(CriticalSectionWrapper::CreateCriticalSection()) {
+PacketRouter::PacketRouter() : transport_seq_(0) {
 }
 
 PacketRouter::~PacketRouter() {
+  DCHECK(rtp_modules_.empty());
 }
 
 void PacketRouter::AddRtpModule(RtpRtcp* rtp_module) {
-  CriticalSectionScoped cs(crit_.get());
+  rtc::CritScope cs(&modules_lock_);
   DCHECK(std::find(rtp_modules_.begin(), rtp_modules_.end(), rtp_module) ==
          rtp_modules_.end());
   rtp_modules_.push_back(rtp_module);
 }
 
 void PacketRouter::RemoveRtpModule(RtpRtcp* rtp_module) {
-  CriticalSectionScoped cs(crit_.get());
-  rtp_modules_.remove(rtp_module);
+  rtc::CritScope cs(&modules_lock_);
+  auto it = std::find(rtp_modules_.begin(), rtp_modules_.end(), rtp_module);
+  DCHECK(it != rtp_modules_.end());
+  rtp_modules_.erase(it);
 }
 
 bool PacketRouter::TimeToSendPacket(uint32_t ssrc,
                                     uint16_t sequence_number,
                                     int64_t capture_timestamp,
                                     bool retransmission) {
-  CriticalSectionScoped cs(crit_.get());
+  rtc::CritScope cs(&modules_lock_);
   for (auto* rtp_module : rtp_modules_) {
     if (rtp_module->SendingMedia() && ssrc == rtp_module->SSRC()) {
       return rtp_module->TimeToSendPacket(ssrc, sequence_number,
                                           capture_timestamp, retransmission);
     }
   }
   return true;
 }
 
-size_t PacketRouter::TimeToSendPadding(size_t bytes) {
-  CriticalSectionScoped cs(crit_.get());
-  for (auto* rtp_module : rtp_modules_) {
-    if (rtp_module->SendingMedia())
-      return rtp_module->TimeToSendPadding(bytes);
+size_t PacketRouter::TimeToSendPadding(size_t bytes_to_send) {
+  size_t total_bytes_sent = 0;
+  rtc::CritScope cs(&modules_lock_);
+  for (RtpRtcp* module : rtp_modules_) {
+    if (module->SendingMedia()) {
+      size_t bytes_sent =
+          module->TimeToSendPadding(bytes_to_send - total_bytes_sent);
+      total_bytes_sent += bytes_sent;
+      if (total_bytes_sent >= bytes_to_send)
+        break;
+    }
   }
-  return 0;
+  return total_bytes_sent;
 }
+
+void PacketRouter::SetTransportWideSequenceNumber(uint16_t sequence_number) {
+  rtc::AtomicOps::ReleaseStore(&transport_seq_, sequence_number);
+}
+
+uint16_t PacketRouter::AllocateSequenceNumber() {
+  int prev_seq = rtc::AtomicOps::AcquireLoad(&transport_seq_);
+  int desired_prev_seq;
+  int new_seq;
+  do {
+    desired_prev_seq = prev_seq;
+    new_seq = (desired_prev_seq + 1) & 0xFFFF;
+    // Note: CompareAndSwap returns the actual value of transport_seq at the
+    // time the CAS operation was executed. Thus, if prev_seq is returned, the
+    // operation was successful - otherwise we need to retry. Saving the
+    // return value saves us a load on retry.
+    prev_seq = rtc::AtomicOps::CompareAndSwap(&transport_seq_, desired_prev_seq,
+                                              new_seq);
+  } while (prev_seq != desired_prev_seq);
+
+  return new_seq;
+}
+
 }  // namespace webrtc