WebRtc libjingle_PeerConnection层（二） CreateOffer

发起视频通话流程图如下

创建dsp描述符,CreateOffer在流程中位于 OnSignalingMessage(offer)

void CConductor::ConnectToPeer(int peer_id) {

    if (peer_connection_.get()) {
        LOG(LS_ERROR) <<
            "We only support connecting to one peer at a time";
        return;
    }

    if (InitializePeerConnection()) {
        peer_connection_->CreateOffer(this, NULL);
    }
    else {
        LOG(LS_ERROR) << "Failed to initialize PeerConnection";
    }
}


void CConductor::OnSuccess(webrtc::SessionDescriptionInterface* desc) {
    peer_connection_->SetLocalDescription(
        DummySetSessionDescriptionObserver::Create(), desc);

    std::string sdp;
    desc->ToString(&sdp);

    // For loopback test. To save some connecting delay.
    if (loopback_) {
        // Replace message type from "offer" to "answer"
        webrtc::SessionDescriptionInterface* session_description(
            webrtc::CreateSessionDescription("answer", sdp));
        peer_connection_->SetRemoteDescription(
            DummySetSessionDescriptionObserver::Create(), session_description);
        return;
    }

    Json::StyledWriter writer;
    Json::Value jmessage;
    jmessage[kSessionDescriptionTypeName] = desc->type();
    jmessage[kSessionDescriptionSdpName] = sdp;
    SendMessage(writer.write(jmessage));
}

void CConductor::OnFailure(const std::string& error) {
    LOG(LERROR) << error;
}

CreateOffer的第一个参数是webrtc:CreateSessionDescriptionObserver，故CConductor继承自webrtc:CreateSessionDescriptionObserver，重写OnSuccess和OnFailure，当调用CreateOffer成功后，OnSuccess会被函数会被触发，就可以获得sdp信息。
再将sdp传递到外部，有通讯现成发送至RemotPeer。

int main(){
    ...

    rtc::Win32Thread w32_thread;
    rtc::ThreadManager::Instance()->SetCurrentThread(&w32_thread);

    ...

    rtc::scoped_refptr conductor(
        new rtc::RefCountedObject(&client, &viceo_show));

    ...

    while ((gm = ::GetMessage(&msg, NULL, 0, 0)) != 0 && gm != -1) {
        ::TranslateMessage(&msg);
        ::DispatchMessage(&msg);
    }

    ...
}

从调试来看webrtc似乎是用了类似Windows的消息机制，很多命令都是通过DispatchMessage来派发消息。
注意如果没有调用rtc::ThreadManager::Instance()->SetCurrentThread(）函数和DispatchMessage，会导致CreateOffer调用后，无法回调OnSuccess。(掉坑了)

调试的时候。仅需在OnSuccess中打断点即可。

仅含工程代码，无webrtc项目源码
http://download.csdn.net/detail/q339659207/9104747