net: Allow connecting to extra outbound peers

src/net.cpp

@@ -1693,6 +1693,36 @@ void CConnman::ProcessOneShot()
     }
 }
 
+bool CConnman::GetTryNewOutboundPeer()
+{
+    return m_try_another_outbound_peer;
+}
+
+void CConnman::SetTryNewOutboundPeer(bool flag)
+{
+    m_try_another_outbound_peer = flag;
+}
+
+// Return the number of peers we have over our outbound connection limit
+// Exclude peers that are marked for disconnect, or are going to be
+// disconnected soon (eg one-shots and feelers)
+// Also exclude peers that haven't finished initial connection handshake yet
+// (so that we don't decide we're over our desired connection limit, and then
+// evict some peer that has finished the handshake)
+int CConnman::GetExtraOutboundCount()
+{
+    int nOutbound = 0;
+    {
+        LOCK(cs_vNodes);
+        for (CNode* pnode : vNodes) {
+            if (!pnode->fInbound && !pnode->m_manual_connection && !pnode->fFeeler && !pnode->fDisconnect && !pnode->fOneShot && pnode->fSuccessfullyConnected) {
+                ++nOutbound;
+            }
+        }
+    }
+    return std::max(nOutbound - nMaxOutbound, 0);
+}
+
 void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
 {
     // Connect to specific addresses
@@ -1781,7 +1811,8 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
         //  * Only make a feeler connection once every few minutes.
         //
         bool fFeeler = false;
-        if (nOutbound >= nMaxOutbound) {
+
+        if (nOutbound >= nMaxOutbound && !GetTryNewOutboundPeer()) {
             int64_t nTime = GetTimeMicros(); // The current time right now (in microseconds).
             if (nTime > nNextFeeler) {
                 nNextFeeler = PoissonNextSend(nTime, FEELER_INTERVAL);
@@ -2204,6 +2235,7 @@ CConnman::CConnman(uint64_t nSeed0In, uint64_t nSeed1In) : nSeed0(nSeed0In), nSe
     semOutbound = nullptr;
     semAddnode = nullptr;
     flagInterruptMsgProc = false;
+    SetTryNewOutboundPeer(false);
 
     Options connOptions;
     Init(connOptions);

src/net.h

@@ -251,6 +251,19 @@ public:
     void GetBanned(banmap_t &banmap);
     void SetBanned(const banmap_t &banmap);
 
+    // This allows temporarily exceeding nMaxOutbound, with the goal of finding
+    // a peer that is better than all our current peers.
+    void SetTryNewOutboundPeer(bool flag);
+    bool GetTryNewOutboundPeer();
+
+    // Return the number of outbound peers we have in excess of our target (eg,
+    // if we previously called SetTryNewOutboundPeer(true), and have since set
+    // to false, we may have extra peers that we wish to disconnect). This may
+    // return a value less than (num_outbound_connections - num_outbound_slots)
+    // in cases where some outbound connections are not yet fully connected, or
+    // not yet fully disconnected.
+    int GetExtraOutboundCount();
+
     bool AddNode(const std::string& node);
     bool RemoveAddedNode(const std::string& node);
     std::vector<AddedNodeInfo> GetAddedNodeInfo();
@@ -413,6 +426,11 @@ private:
     std::thread threadOpenAddedConnections;
     std::thread threadOpenConnections;
     std::thread threadMessageHandler;
+
+    /** flag for deciding to connect to an extra outbound peer,
+     *  in excess of nMaxOutbound
+     *  This takes the place of a feeler connection */
+    std::atomic_bool m_try_another_outbound_peer;
 };
 extern std::unique_ptr<CConnman> g_connman;
 void Discover(boost::thread_group& threadGroup);