[core] Refax: safety improvements for RCV loss list and closing state (…

…#2517)

srtcore/api.h

@@ -193,6 +193,15 @@ class CUDTSocket
     /// to finish sending the data that were scheduled for sending so far.
     void setClosed();
 
+    // This is necessary to be called from the group before the group clears
+    // the connection with the socket. As for managed groups (and there are
+    // currently no other group types), a socket disconnected from the group
+    // is no longer usable.
+    void setClosing()
+    {
+        core().m_bClosing = true;
+    }
+
     /// This does the same as setClosed, plus sets the m_bBroken to true.
     /// Such a socket can still be read from so that remaining data from
     /// the receiver buffer can be read, but no longer sends anything.

srtcore/core.cpp

@@ -11089,7 +11089,10 @@ int srt::CUDT::checkNAKTimer(const steady_clock::time_point& currtime)
      * not knowing what to retransmit when the only NAK sent by receiver is lost,
      * all packets past last ACK are retransmitted (rexmitMethod() == SRM_FASTREXMIT).
      */
+    enterCS(m_RcvLossLock);
     const int loss_len = m_pRcvLossList->getLossLength();
+    leaveCS(m_RcvLossLock);
+
     SRT_ASSERT(loss_len >= 0);
     int debug_decision = BECAUSE_NO_REASON;
 

srtcore/group.cpp

@@ -893,6 +893,16 @@ void CUDTGroup::close()
                 HLOGC(smlog.Debug, log << "group/close: IPE(NF): group member @" << ig->id << " already deleted");
                 continue;
             }
+
+            // Make the socket closing BEFORE withdrawing its group membership
+            // because a socket created as a group member cannot be valid
+            // without the group.
+            // This is not true in case of non-managed groups, which
+            // only collect sockets, but also non-managed groups should not
+            // use common group buffering and tsbpd. Also currently there are
+            // no other groups than managed one.
+            s->setClosing();
+
             s->m_GroupOf = NULL;
             s->m_GroupMemberData = NULL;
             HLOGC(smlog.Debug, log << "group/close: CUTTING OFF @" << ig->id << " (found as @" << s->m_SocketID << ") from the group");