net: remove cs_vRecvMsg

vRecvMsg is now only touched by the socket handler thread.

The accounting vars (nRecvBytes/nLastRecv/mapRecvBytesPerMsgCmd) are also
only used by the socket handler thread, with the exception of queries from
rpc/gui. These accesses are not threadsafe, but they never were. This needs to
be addressed separately.

Also, update comment describing data flow

src/net.cpp

@@ -644,7 +644,6 @@ void CNode::copyStats(CNodeStats &stats)
 }
 #undef X
 
-// requires LOCK(cs_vRecvMsg)
 bool CNode::ReceiveMsgBytes(const char *pch, unsigned int nBytes, bool& complete)
 {
     complete = false;
@@ -1079,16 +1078,12 @@ void CConnman::ThreadSocketHandler()
                     {
                         TRY_LOCK(pnode->cs_vSend, lockSend);
                         if (lockSend)
-                        {
-                            TRY_LOCK(pnode->cs_vRecvMsg, lockRecv);
-                            if (lockRecv)
                         {
                                 TRY_LOCK(pnode->cs_inventory, lockInv);
                                 if (lockInv)
                                     fDelete = true;
                         }
                     }
-                    }
                     if (fDelete)
                     {
                         vNodesDisconnected.remove(pnode);
@@ -1146,15 +1141,10 @@ void CConnman::ThreadSocketHandler()
                 //   write buffer in this case before receiving more. This avoids
                 //   needlessly queueing received data, if the remote peer is not themselves
                 //   receiving data. This means properly utilizing TCP flow control signalling.
-                // * Otherwise, if there is no (complete) message in the receive buffer,
-                //   or there is space left in the buffer, select() for receiving data.
-                // * (if neither of the above applies, there is certainly one message
-                //   in the receiver buffer ready to be processed).
-                // Together, that means that at least one of the following is always possible,
-                // so we don't deadlock:
-                // * We send some data.
-                // * We wait for data to be received (and disconnect after timeout).
-                // * We process a message in the buffer (message handler thread).
+                // * Otherwise, if there is space left in the receive buffer, select() for
+                //   receiving data.
+                // * Hand off all complete messages to the processor, to be handled without
+                //   blocking here.
                 {
                     TRY_LOCK(pnode->cs_vSend, lockSend);
                     if (lockSend) {
@@ -1165,8 +1155,7 @@ void CConnman::ThreadSocketHandler()
                     }
                 }
                 {
-                    TRY_LOCK(pnode->cs_vRecvMsg, lockRecv);
-                    if (lockRecv && !pnode->fPauseRecv)
+                    if (!pnode->fPauseRecv)
                         FD_SET(pnode->hSocket, &fdsetRecv);
                 }
             }
@@ -1225,8 +1214,6 @@ void CConnman::ThreadSocketHandler()
                 continue;
             if (FD_ISSET(pnode->hSocket, &fdsetRecv) || FD_ISSET(pnode->hSocket, &fdsetError))
             {
-                TRY_LOCK(pnode->cs_vRecvMsg, lockRecv);
-                if (lockRecv)
                 {
                     {
                         // typical socket buffer is 8K-64K
@@ -1865,14 +1852,8 @@ void CConnman::ThreadMessageHandler()
                 continue;
 
             // Receive messages
-            {
-                TRY_LOCK(pnode->cs_vRecvMsg, lockRecv);
-                if (lockRecv)
-                {
             bool fMoreNodeWork = GetNodeSignals().ProcessMessages(pnode, *this, flagInterruptMsgProc);
             fMoreWork |= (fMoreNodeWork && !pnode->fPauseSend);
-                }
-            }
             if (flagInterruptMsgProc)
                 return;
 

src/net.h

@@ -613,8 +613,6 @@ public:
     size_t nProcessQueueSize;
 
     std::deque<CInv> vRecvGetData;
-    std::list<CNetMessage> vRecvMsg;
-    CCriticalSection cs_vRecvMsg;
     uint64_t nRecvBytes;
     std::atomic<int> nRecvVersion;
 
@@ -726,6 +724,7 @@ private:
     const ServiceFlags nLocalServices;
     const int nMyStartingHeight;
     int nSendVersion;
+    std::list<CNetMessage> vRecvMsg;  // Used only by SocketHandler thread
 public:
 
     NodeId GetId() const {
@@ -746,7 +745,6 @@ public:
         return nRefCount;
     }
 
-    // requires LOCK(cs_vRecvMsg)
     bool ReceiveMsgBytes(const char *pch, unsigned int nBytes, bool& complete);
 
     void SetRecvVersion(int nVersionIn)

src/net_processing.cpp

@@ -2439,7 +2439,6 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     return true;
 }
 
-// requires LOCK(cs_vRecvMsg)
 bool ProcessMessages(CNode* pfrom, CConnman& connman, std::atomic<bool>& interruptMsgProc)
 {
     const CChainParams& chainparams = Params();