防止nack异步触发时对象析构导致的崩溃

webrtc/WebRtcTransport.cpp

@@ -760,10 +760,15 @@ void WebRtcTransportImp::onRtcp(const char *buf, size_t len) {
 void WebRtcTransportImp::createRtpChannel(const string &rid, uint32_t ssrc, const MediaTrack::Ptr &track) {
     //rid --> RtpReceiverImp
     auto &ref = track->rtp_channel[rid];
+    weak_ptr<WebRtcTransportImp> weak_self = dynamic_pointer_cast<WebRtcTransportImp>(shared_from_this());
     ref = std::make_shared<RtpChannel>(getPoller(),[track, this, rid](RtpPacket::Ptr rtp) mutable {
         onSortedRtp(*track, rid, std::move(rtp));
-    }, [track, this, ssrc](const FCI_NACK &nack) mutable {
-        onSendNack(*track, nack, ssrc);
+    }, [track, weak_self, ssrc](const FCI_NACK &nack) mutable {
+        //nack发送可能由定时器异步触发
+        auto strong_self = weak_self.lock();
+        if (strong_self) {
+            strong_self->onSendNack(*track, nack, ssrc);
+        }
     });
     InfoL << "create rtp receiver of ssrc:" << ssrc << ", rid:" << rid << ", codec:" << track->plan_rtp->codec;
 }