Merge #7438: Do not absolutely protect local peers; decide group ties based on time.

8e09f91 Decide eviction group ties based on time. (Gregory Maxwell)
46dbcd4 Do not absolutely protect local peers from eviction. (Gregory Maxwell)

Author: laanwj

src/net.cpp

@@ -884,8 +884,6 @@ static bool AttemptToEvictConnection(bool fPreferNewConnection) {
                 continue;
             if (node->fDisconnect)
                 continue;
-            if (node->addr.IsLocal())
-                continue;
             vEvictionCandidates.push_back(CNodeRef(node));
         }
     }
@@ -916,30 +914,34 @@ static bool AttemptToEvictConnection(bool fPreferNewConnection) {
 
     if (vEvictionCandidates.empty()) return false;
 
-    // Identify the network group with the most connections
+    // Identify the network group with the most connections and youngest member.
+    // (vEvictionCandidates is already sorted by reverse connect time)
     std::vector<unsigned char> naMostConnections;
     unsigned int nMostConnections = 0;
+    int64_t nMostConnectionsTime = 0;
     std::map<std::vector<unsigned char>, std::vector<CNodeRef> > mapAddrCounts;
     BOOST_FOREACH(const CNodeRef &node, vEvictionCandidates) {
         mapAddrCounts[node->addr.GetGroup()].push_back(node);
+        int64_t grouptime = mapAddrCounts[node->addr.GetGroup()][0]->nTimeConnected;
+        size_t groupsize = mapAddrCounts[node->addr.GetGroup()].size();
 
-        if (mapAddrCounts[node->addr.GetGroup()].size() > nMostConnections) {
-            nMostConnections = mapAddrCounts[node->addr.GetGroup()].size();
+        if (groupsize > nMostConnections || (groupsize == nMostConnections && grouptime > nMostConnectionsTime)) {
+            nMostConnections = groupsize;
+            nMostConnectionsTime = grouptime;
             naMostConnections = node->addr.GetGroup();
         }
     }
 
     // Reduce to the network group with the most connections
     vEvictionCandidates = mapAddrCounts[naMostConnections];
 
-    // Do not disconnect peers if there is only 1 connection from their network group
+    // Do not disconnect peers if there is only one unprotected connection from their network group.
     if (vEvictionCandidates.size() <= 1)
         // unless we prefer the new connection (for whitelisted peers)
         if (!fPreferNewConnection)
             return false;
 
-    // Disconnect the most recent connection from the network group with the most connections
-    std::sort(vEvictionCandidates.begin(), vEvictionCandidates.end(), ReverseCompareNodeTimeConnected);
+    // Disconnect from the network group with the most connections
     vEvictionCandidates[0]->fDisconnect = true;
 
     return true;