net: add a new message queue for the message processor

This separates the storage of messages from the net and queued messages for
processing, allowing the locks to be split.

src/net.cpp

@@ -1239,8 +1239,18 @@ void CConnman::ThreadSocketHandler()
                             if (!pnode->ReceiveMsgBytes(pchBuf, nBytes, notify))
                                 pnode->CloseSocketDisconnect();
                             RecordBytesRecv(nBytes);
-                            if (notify)
+                            if (notify) {
+                                auto it(pnode->vRecvMsg.begin());
+                                for (; it != pnode->vRecvMsg.end(); ++it) {
+                                    if (!it->complete())
+                                        break;
+                                }
+                                {
+                                    LOCK(pnode->cs_vProcessMsg);
+                                    pnode->vProcessMsg.splice(pnode->vProcessMsg.end(), pnode->vRecvMsg, pnode->vRecvMsg.begin(), it);
+                                }
                                 WakeMessageHandler();
+                            }
                         }
                         else if (nBytes == 0)
                         {

src/net.h

@@ -608,6 +608,9 @@ public:
     std::deque<std::vector<unsigned char>> vSendMsg;
     CCriticalSection cs_vSend;
 
+    CCriticalSection cs_vProcessMsg;
+    std::list<CNetMessage> vProcessMsg;
+
     std::deque<CInv> vRecvGetData;
     std::list<CNetMessage> vRecvMsg;
     CCriticalSection cs_vRecvMsg;

src/net_processing.cpp

@@ -2468,21 +2468,16 @@ bool ProcessMessages(CNode* pfrom, CConnman& connman, std::atomic<bool>& interru
         if (pfrom->nSendSize >= nMaxSendBufferSize)
             return false;
 
-        auto it = pfrom->vRecvMsg.begin();
-        if (it == pfrom->vRecvMsg.end())
-            return false;
-
-        // end, if an incomplete message is found
-        if (!it->complete())
-            return false;
-
-        // get next message
-        CNetMessage msg = std::move(*it);
-
-        // at this point, any failure means we can delete the current message
-        pfrom->vRecvMsg.erase(pfrom->vRecvMsg.begin());
-
-        fMoreWork = !pfrom->vRecvMsg.empty() && pfrom->vRecvMsg.front().complete();
+        std::list<CNetMessage> msgs;
+        {
+            LOCK(pfrom->cs_vProcessMsg);
+            if (pfrom->vProcessMsg.empty())
+                return false;
+            // Just take one message
+            msgs.splice(msgs.begin(), pfrom->vProcessMsg, pfrom->vProcessMsg.begin());
+            fMoreWork = !pfrom->vProcessMsg.empty();
+        }
+        CNetMessage& msg(msgs.front());
 
         msg.SetVersion(pfrom->GetRecvVersion());
         // Scan for message start