收集Candidate的时机

收集Candidate的代码调用过程

JsepTransportController::MaybeStartGathering

h:\webrtc-20210315\webrtc-20210315\webrtc\webrtc-checkout\src\pc\jsep_transport_controller.cc

JsepTransportController::GetDtlsTransport

jseptransport_by_name一般只有一项，因为rtp和rtcp都是复用同一个端口。

jseptransport_by_name

启动AllocationSequence

AllocationSequence::Start

在AllocationSequence::OnMessage中判断收到MSG_ALLOCATION_PHASE消息。

AllocationSequence::OnMessage

void AllocationSequence::OnMessage(rtc::Message* msg) {
  RTC_DCHECK(rtc::Thread::Current() == session_->network_thread());
  RTC_DCHECK(msg->message_id == MSG_ALLOCATION_PHASE);
  const char* const PHASE_NAMES[kNumPhases] = {"Udp", "Relay", "Tcp"};
  // Perform all of the phases in the current step.
  RTC_LOG(LS_INFO) << network_->ToString()
                   << ": Allocation Phase=" << PHASE_NAMES[phase_];
  switch (phase_) {
    case PHASE_UDP:
      CreateUDPPorts();
      CreateStunPorts();
      break;
    case PHASE_RELAY:
      CreateRelayPorts();
      break;
    case PHASE_TCP:
      CreateTCPPorts();
      state_ = kCompleted;
      break;
    default:
      RTC_NOTREACHED();
  }
  if (state() == kRunning) {
    ++phase_;
    session_->network_thread()->PostDelayed(RTC_FROM_HERE,
                                            session_->allocator()->step_delay(),
                                            this, MSG_ALLOCATION_PHASE);
  } else {
    // If all phases in AllocationSequence are completed, no allocation
    // steps needed further. Canceling  pending signal.
    session_->network_thread()->Clear(this, MSG_ALLOCATION_PHASE);
    SignalPortAllocationComplete(this);
  }
}

刚开始会收到PHASE_UDP，后面会收到PHASE_RELAY消息。

小结