1 files changed, 33 insertions, 29 deletions

diff --git a/src/net.cpp b/src/net.cpp
index 755312682..54ed1d9b5 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -48,6 +48,7 @@ static CNode* pnodeSync = NULL;
 uint64 nLocalHostNonce = 0;
 static std::vector<SOCKET> vhListenSocket;
 CAddrMan addrman;
+int nMaxConnections = 125;
 
 vector<CNode*> vNodes;
 CCriticalSection cs_vNodes;
@@ -840,19 +841,39 @@ void ThreadSocketHandler()
             {
                 if (pnode->hSocket == INVALID_SOCKET)
                     continue;
+                FD_SET(pnode->hSocket, &fdsetError);
+                hSocketMax = max(hSocketMax, pnode->hSocket);
+                have_fds = true;
+
+                // Implement the following logic:
+                // * If there is data to send, select() for sending data. As this only
+                //   happens when optimistic write failed, we choose to first drain the
+                //   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).
                 {
                     TRY_LOCK(pnode->cs_vSend, lockSend);
-                    if (lockSend) {
-                        // do not read, if draining write queue
-                        if (!pnode->vSendMsg.empty())
-                            FD_SET(pnode->hSocket, &fdsetSend);
-                        else
-                            FD_SET(pnode->hSocket, &fdsetRecv);
-                        FD_SET(pnode->hSocket, &fdsetError);
-                        hSocketMax = max(hSocketMax, pnode->hSocket);
-                        have_fds = true;
+                    if (lockSend && !pnode->vSendMsg.empty()) {
+                        FD_SET(pnode->hSocket, &fdsetSend);
+                        continue;
                     }
                 }
+                {
+                    TRY_LOCK(pnode->cs_vRecvMsg, lockRecv);
+                    if (lockRecv && (
+                        pnode->vRecvMsg.empty() || !pnode->vRecvMsg.front().complete() ||
+                        pnode->GetTotalRecvSize() <= ReceiveFloodSize()))
+                        FD_SET(pnode->hSocket, &fdsetRecv);
+                }
             }
         }
 
@@ -908,7 +929,7 @@ void ThreadSocketHandler()
                 if (nErr != WSAEWOULDBLOCK)
                     printf("socket error accept failed: %d\n", nErr);
             }
-            else if (nInbound >= GetArg("-maxconnections", 125) - MAX_OUTBOUND_CONNECTIONS)
+            else if (nInbound >= nMaxConnections - MAX_OUTBOUND_CONNECTIONS)
             {
                 {
                     LOCK(cs_setservAddNodeAddresses);
@@ -958,12 +979,7 @@ void ThreadSocketHandler()
                 TRY_LOCK(pnode->cs_vRecvMsg, lockRecv);
                 if (lockRecv)
                 {
-                    if (pnode->GetTotalRecvSize() > ReceiveFloodSize()) {
-                        if (!pnode->fDisconnect)
-                            printf("socket recv flood control disconnect (%u bytes)\n", pnode->GetTotalRecvSize());
-                        pnode->CloseSocketDisconnect();
-                    }
-                    else {
+                    {
                         // typical socket buffer is 8K-64K
                         char pchBuf[0x10000];
                         int nBytes = recv(pnode->hSocket, pchBuf, sizeof(pchBuf), MSG_DONTWAIT);
@@ -1653,18 +1669,6 @@ bool BindListenPort(const CService &addrBind, string& strError)
     strError = "";
     int nOne = 1;
 
-#ifdef WIN32
-    // Initialize Windows Sockets
-    WSADATA wsadata;
-    int ret = WSAStartup(MAKEWORD(2,2), &wsadata);
-    if (ret != NO_ERROR)
-    {
-        strError = strprintf("Error: TCP/IP socket library failed to start (WSAStartup returned error %d)", ret);
-        printf("%s\n", strError.c_str());
-        return false;
-    }
-#endif
-
     // Create socket for listening for incoming connections
 #ifdef USE_IPV6
     struct sockaddr_storage sockaddr;
@@ -1815,7 +1819,7 @@ void StartNode(boost::thread_group& threadGroup)
 {
     if (semOutbound == NULL) {
         // initialize semaphore
-        int nMaxOutbound = min(MAX_OUTBOUND_CONNECTIONS, (int)GetArg("-maxconnections", 125));
+        int nMaxOutbound = min(MAX_OUTBOUND_CONNECTIONS, nMaxConnections);
         semOutbound = new CSemaphore(nMaxOutbound);
     }