net: Drop CNodeRef for AttemptToEvictConnection

Locking for each operation here is unnecessary, and solves the wrong problem.
Additionally, it introduces a problem when cs_vNodes is held in an owning
class, to which invididual CNodeRefs won't have access.

These should be weak pointers anyway, once vNodes contain shared pointers.

Rather than using a refcounting class, use a 3-step process instead.

1. Lock vNodes long enough to snapshot the fields necessary for comparing
2. Unlock and do the comparison
3. Re-lock and mark the resulting node for disconnection if it still exists

Zcash: add nVersion to NodeEvictionCandidate

src/net.cpp

@@ -713,51 +713,23 @@ void SocketSendData(CNode *pnode)
 
 static list<CNode*> vNodesDisconnected;
 
-class CNodeRef {
-public:
-    CNodeRef(CNode *pnode) : _pnode(pnode) {
-        LOCK(cs_vNodes);
-        _pnode->AddRef();
-    }
-
-    ~CNodeRef() {
-        LOCK(cs_vNodes);
-        _pnode->Release();
-    }
-
-    CNode& operator *() const {return *_pnode;};
-    CNode* operator ->() const {return _pnode;};
-
-    CNodeRef& operator =(const CNodeRef& other)
-    {
-        if (this != &other) {
-            LOCK(cs_vNodes);
-
-            _pnode->Release();
-            _pnode = other._pnode;
-            _pnode->AddRef();
-        }
-        return *this;
-    }
-
-    CNodeRef(const CNodeRef& other):
-        _pnode(other._pnode)
-    {
-        LOCK(cs_vNodes);
-        _pnode->AddRef();
-    }
-private:
-    CNode *_pnode;
+struct NodeEvictionCandidate
+{
+    NodeId id;
+    int64_t nTimeConnected;
+    int64_t nMinPingUsecTime;
+    CAddress addr;
+    int nVersion;
 };
 
-static bool ReverseCompareNodeMinPingTime(const CNodeRef &a, const CNodeRef &b)
+static bool ReverseCompareNodeMinPingTime(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
 {
-    return a->nMinPingUsecTime > b->nMinPingUsecTime;
+    return a.nMinPingUsecTime > b.nMinPingUsecTime;
 }
 
-static bool ReverseCompareNodeTimeConnected(const CNodeRef &a, const CNodeRef &b)
+static bool ReverseCompareNodeTimeConnected(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
 {
-    return a->nTimeConnected > b->nTimeConnected;
+    return a.nTimeConnected > b.nTimeConnected;
 }
 
 class CompareNetGroupKeyed
@@ -770,14 +742,14 @@ public:
         GetRandBytes(vchSecretKey.data(), vchSecretKey.size());
     }
 
-    bool operator()(const CNodeRef &a, const CNodeRef &b)
+    bool operator()(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
     {
         std::vector<unsigned char> vchGroupA, vchGroupB;
         CSHA256 hashA, hashB;
         std::vector<unsigned char> vchA(32), vchB(32);
 
-        vchGroupA = a->addr.GetGroup();
-        vchGroupB = b->addr.GetGroup();
+        vchGroupA = a.addr.GetGroup();
+        vchGroupB = b.addr.GetGroup();
 
         hashA.Write(begin_ptr(vchGroupA), vchGroupA.size());
         hashB.Write(begin_ptr(vchGroupB), vchGroupB.size());
@@ -793,7 +765,7 @@ public:
 };
 
 static bool AttemptToEvictConnection(bool fPreferNewConnection) {
-    std::vector<CNodeRef> vEvictionCandidates;
+    std::vector<NodeEvictionCandidate> vEvictionCandidates;
     {
         LOCK(cs_vNodes);
 
@@ -804,7 +776,14 @@ static bool AttemptToEvictConnection(bool fPreferNewConnection) {
                 continue;
             if (node->fDisconnect)
                 continue;
-            vEvictionCandidates.push_back(CNodeRef(node));
+            NodeEvictionCandidate candidate = {
+                .id = node->id,
+                .nTimeConnected = node->nTimeConnected,
+                .nMinPingUsecTime = node->nMinPingUsecTime,
+                .addr = node->addr,
+                .nVersion = node -> nVersion
+            };
+            vEvictionCandidates.push_back(candidate);
         }
     }
 
@@ -813,7 +792,7 @@ static bool AttemptToEvictConnection(bool fPreferNewConnection) {
     // Protect connections with certain characteristics
 
     // Check version of eviction candidates and prioritize nodes which do not support network upgrade.
-    std::vector<CNodeRef> vTmpEvictionCandidates;
+    std::vector<NodeEvictionCandidate> vTmpEvictionCandidates;
     int height;
     {
         LOCK(cs_main);
@@ -831,8 +810,8 @@ static bool AttemptToEvictConnection(bool fPreferNewConnection) {
             height >= nActivationHeight - NETWORK_UPGRADE_PEER_PREFERENCE_BLOCK_PERIOD)
         {
             // Find any nodes which don't support the protocol version for the next upgrade
-            for (const CNodeRef &node : vEvictionCandidates) {
-                if (node->nVersion < params.vUpgrades[idx].nProtocolVersion &&
+            for (const NodeEvictionCandidate &node : vEvictionCandidates) {
+                if (node.nVersion < params.vUpgrades[idx].nProtocolVersion &&
                     !(
                         Params().NetworkIDString() == "regtest" &&
                         !GetBoolArg("-nurejectoldversions", DEFAULT_NU_REJECT_OLD_VERSIONS)
@@ -876,16 +855,16 @@ static bool AttemptToEvictConnection(bool fPreferNewConnection) {
     std::vector<unsigned char> naMostConnections;
     unsigned int nMostConnections = 0;
     int64_t nMostConnectionsTime = 0;
-    std::map<std::vector<unsigned char>, std::vector<CNodeRef> > mapAddrCounts;
-    for (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();
+    std::map<std::vector<unsigned char>, std::vector<NodeEvictionCandidate> > mapAddrCounts;
+    for(const NodeEvictionCandidate &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 (groupsize > nMostConnections || (groupsize == nMostConnections && grouptime > nMostConnectionsTime)) {
             nMostConnections = groupsize;
             nMostConnectionsTime = grouptime;
-            naMostConnections = node->addr.GetGroup();
+            naMostConnections = node.addr.GetGroup();
         }
     }
 
@@ -899,9 +878,15 @@ static bool AttemptToEvictConnection(bool fPreferNewConnection) {
             return false;
 
     // Disconnect from the network group with the most connections
-    vEvictionCandidates[0]->fDisconnect = true;
-
-    return true;
+    NodeId evicted = vEvictionCandidates.front().id;
+    LOCK(cs_vNodes);
+    for(std::vector<CNode*>::const_iterator it(vNodes.begin()); it != vNodes.end(); ++it) {
+        if ((*it)->GetId() == evicted) {
+            (*it)->fDisconnect = true;
+            return true;
+        }
+    }
+    return false;
 }
 
 static void AcceptConnection(const ListenSocket& hListenSocket) {