Merge #19910: net processing: Move peer_map to PeerManager

3025ca9e7743d9b96c22e9c6ed7ef051dcea7e54 [net processing] Add RemovePeer() (John Newbery)
a20ab22786466fe5164b53e62de9d23a4062fbca [net processing] Make GetPeerRef const (John Newbery)
ed7e469ceec6f7101a3fb7b15c21a6fb69697866 [net_processing] Move peer_map to PeerManager (John Newbery)
a529fd3e3f2391e592ac937e291fec51e067ea2e [net processing] Move GetNodeStateStats into PeerManager (John Newbery)

Pull request description:

  This moves `g_peer_map` from a global in net_processing.cpp's unnamed namespace to being a member `m_peer_map` of `PeerManager`.

ACKs for top commit:
  theuni:
    Re-ACK 3025ca9e7743d9b96c22e9c6ed7ef051dcea7e54.
  dongcarl:
    Re-ACK 3025ca9
  hebasto:
    re-ACK 3025ca9e7743d9b96c22e9c6ed7ef051dcea7e54, since my [previous](https://github.com/bitcoin/bitcoin/pull/19910#pullrequestreview-545574237) review only reverted the change that introduced NRVO in `PeerManager::GetPeerRef`, and comments are fixed in the proper commits.

Tree-SHA512: 6369eb3c688ac5b84f89f7674115f78ff02edbed76063ac2ebb1759894c9e973883e10821a35dab92bd3d738280acc095bd5368f552a060b83cd309330387d47

4 files changed, 94 insertions, 74 deletions

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 7c4ba458c3..b7dd54e55e 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -422,58 +422,6 @@ static CNodeState *State(NodeId pnode) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
     return &it->second;
 }
 
-/**
- * Data structure for an individual peer. This struct is not protected by
- * cs_main since it does not contain validation-critical data.
- *
- * Memory is owned by shared pointers and this object is destructed when
- * the refcount drops to zero.
- *
- * TODO: move most members from CNodeState to this structure.
- * TODO: move remaining application-layer data members from CNode to this structure.
- */
-struct Peer {
-    /** Same id as the CNode object for this peer */
-    const NodeId m_id{0};
-
-    /** Protects misbehavior data members */
-    Mutex m_misbehavior_mutex;
-    /** Accumulated misbehavior score for this peer */
-    int m_misbehavior_score GUARDED_BY(m_misbehavior_mutex){0};
-    /** Whether this peer should be disconnected and marked as discouraged (unless it has the noban permission). */
-    bool m_should_discourage GUARDED_BY(m_misbehavior_mutex){false};
-
-    /** Set of txids to reconsider once their parent transactions have been accepted **/
-    std::set<uint256> m_orphan_work_set GUARDED_BY(g_cs_orphans);
-
-    /** Protects m_getdata_requests **/
-    Mutex m_getdata_requests_mutex;
-    /** Work queue of items requested by this peer **/
-    std::deque<CInv> m_getdata_requests GUARDED_BY(m_getdata_requests_mutex);
-
-    explicit Peer(NodeId id) : m_id(id) {}
-};
-
-using PeerRef = std::shared_ptr<Peer>;
-
-/**
- * Map of all Peer objects, keyed by peer id. This map is protected
- * by the global g_peer_mutex. Once a shared pointer reference is
- * taken, the lock may be released. Individual fields are protected by
- * their own locks.
- */
-Mutex g_peer_mutex;
-static std::map<NodeId, PeerRef> g_peer_map GUARDED_BY(g_peer_mutex);
-
-/** Get a shared pointer to the Peer object.
- *  May return nullptr if the Peer object can't be found. */
-static PeerRef GetPeerRef(NodeId id)
-{
-    LOCK(g_peer_mutex);
-    auto it = g_peer_map.find(id);
-    return it != g_peer_map.end() ? it->second : nullptr;
-}
-
 static void UpdatePreferredDownload(const CNode& node, CNodeState* state) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     nPreferredDownload -= state->fPreferredDownload;
@@ -807,8 +755,8 @@ void PeerManager::InitializeNode(CNode *pnode) {
     }
     {
         PeerRef peer = std::make_shared<Peer>(nodeid);
-        LOCK(g_peer_mutex);
-        g_peer_map.emplace_hint(g_peer_map.end(), nodeid, std::move(peer));
+        LOCK(m_peer_mutex);
+        m_peer_map.emplace_hint(m_peer_map.end(), nodeid, std::move(peer));
     }
     if (!pnode->IsInboundConn()) {
         PushNodeVersion(*pnode, m_connman, GetTime());
@@ -842,11 +790,9 @@ void PeerManager::FinalizeNode(const CNode& node, bool& fUpdateConnectionTime) {
     LOCK(cs_main);
     int misbehavior{0};
     {
-        PeerRef peer = GetPeerRef(nodeid);
+        PeerRef peer = RemovePeer(nodeid);
         assert(peer != nullptr);
         misbehavior = WITH_LOCK(peer->m_misbehavior_mutex, return peer->m_misbehavior_score);
-        LOCK(g_peer_mutex);
-        g_peer_map.erase(nodeid);
     }
     CNodeState *state = State(nodeid);
     assert(state != nullptr);
@@ -887,7 +833,26 @@ void PeerManager::FinalizeNode(const CNode& node, bool& fUpdateConnectionTime) {
     LogPrint(BCLog::NET, "Cleared nodestate for peer=%d\n", nodeid);
 }
 
-bool GetNodeStateStats(NodeId nodeid, CNodeStateStats &stats) {
+PeerRef PeerManager::GetPeerRef(NodeId id) const
+{
+    LOCK(m_peer_mutex);
+    auto it = m_peer_map.find(id);
+    return it != m_peer_map.end() ? it->second : nullptr;
+}
+
+PeerRef PeerManager::RemovePeer(NodeId id)
+{
+    PeerRef ret;
+    LOCK(m_peer_mutex);
+    auto it = m_peer_map.find(id);
+    if (it != m_peer_map.end()) {
+        ret = std::move(it->second);
+        m_peer_map.erase(it);
+    }
+    return ret;
+}
+
+bool PeerManager::GetNodeStateStats(NodeId nodeid, CNodeStateStats &stats) {
     {
         LOCK(cs_main);
         CNodeState* state = State(nodeid);
diff --git a/src/net_processing.h b/src/net_processing.h
index 87eee566de..c179b89ebe 100644
--- a/src/net_processing.h
+++ b/src/net_processing.h
@@ -32,6 +32,47 @@ static const bool DEFAULT_PEERBLOCKFILTERS = false;
 /** Threshold for marking a node to be discouraged, e.g. disconnected and added to the discouragement filter. */
 static const int DISCOURAGEMENT_THRESHOLD{100};
 
+struct CNodeStateStats {
+    int m_misbehavior_score = 0;
+    int nSyncHeight = -1;
+    int nCommonHeight = -1;
+    std::vector<int> vHeightInFlight;
+};
+
+/**
+ * Data structure for an individual peer. This struct is not protected by
+ * cs_main since it does not contain validation-critical data.
+ *
+ * Memory is owned by shared pointers and this object is destructed when
+ * the refcount drops to zero.
+ *
+ * TODO: move most members from CNodeState to this structure.
+ * TODO: move remaining application-layer data members from CNode to this structure.
+ */
+struct Peer {
+    /** Same id as the CNode object for this peer */
+    const NodeId m_id{0};
+
+    /** Protects misbehavior data members */
+    Mutex m_misbehavior_mutex;
+    /** Accumulated misbehavior score for this peer */
+    int m_misbehavior_score GUARDED_BY(m_misbehavior_mutex){0};
+    /** Whether this peer should be disconnected and marked as discouraged (unless it has the noban permission). */
+    bool m_should_discourage GUARDED_BY(m_misbehavior_mutex){false};
+
+    /** Set of txids to reconsider once their parent transactions have been accepted **/
+    std::set<uint256> m_orphan_work_set GUARDED_BY(g_cs_orphans);
+
+    /** Protects m_getdata_requests **/
+    Mutex m_getdata_requests_mutex;
+    /** Work queue of items requested by this peer **/
+    std::deque<CInv> m_getdata_requests GUARDED_BY(m_getdata_requests_mutex);
+
+    explicit Peer(NodeId id) : m_id(id) {}
+};
+
+using PeerRef = std::shared_ptr<Peer>;
+
 class PeerManager final : public CValidationInterface, public NetEventsInterface {
 public:
     PeerManager(const CChainParams& chainparams, CConnman& connman, BanMan* banman,
@@ -94,7 +135,18 @@ public:
      */
     void Misbehaving(const NodeId pnode, const int howmuch, const std::string& message);
 
+    /** Get statistics from node state */
+    bool GetNodeStateStats(NodeId nodeid, CNodeStateStats& stats);
+
 private:
+    /** Get a shared pointer to the Peer object.
+     *  May return an empty shared_ptr if the Peer object can't be found. */
+    PeerRef GetPeerRef(NodeId id) const;
+
+    /** Get a shared pointer to the Peer object and remove it from m_peer_map.
+     *  May return an empty shared_ptr if the Peer object can't be found. */
+    PeerRef RemovePeer(NodeId id);
+
     /**
      * Potentially mark a node discouraged based on the contents of a BlockValidationState object
      *
@@ -143,18 +195,18 @@ private:
     TxRequestTracker m_txrequest GUARDED_BY(::cs_main);
 
     int64_t m_stale_tip_check_time; //!< Next time to check for stale tip
-};
 
-struct CNodeStateStats {
-    int m_misbehavior_score = 0;
-    int nSyncHeight = -1;
-    int nCommonHeight = -1;
-    std::vector<int> vHeightInFlight;
+    /** Protects m_peer_map */
+    mutable Mutex m_peer_mutex;
+    /**
+     * Map of all Peer objects, keyed by peer id. This map is protected
+     * by the m_peer_mutex. Once a shared pointer reference is
+     * taken, the lock may be released. Individual fields are protected by
+     * their own locks.
+     */
+    std::map<NodeId, PeerRef> m_peer_map GUARDED_BY(m_peer_mutex);
 };
 
-/** Get statistics from node state */
-bool GetNodeStateStats(NodeId nodeid, CNodeStateStats &stats);
-
 /** Relay transaction to every node */
 void RelayTransaction(const uint256& txid, const uint256& wtxid, const CConnman& connman) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index a872067b82..317a5c7cbe 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -121,11 +121,13 @@ public:
             }
 
             // Try to retrieve the CNodeStateStats for each node.
-            TRY_LOCK(::cs_main, lockMain);
-            if (lockMain) {
-                for (auto& node_stats : stats) {
-                    std::get<1>(node_stats) =
-                        GetNodeStateStats(std::get<0>(node_stats).nodeid, std::get<2>(node_stats));
+            if (m_context->peerman) {
+                TRY_LOCK(::cs_main, lockMain);
+                if (lockMain) {
+                    for (auto& node_stats : stats) {
+                        std::get<1>(node_stats) =
+                            m_context->peerman->GetNodeStateStats(std::get<0>(node_stats).nodeid, std::get<2>(node_stats));
+                    }
                 }
             }
             return true;
diff --git a/src/rpc/net.cpp b/src/rpc/net.cpp
index e72ef24d12..fa71ea1181 100644
--- a/src/rpc/net.cpp
+++ b/src/rpc/net.cpp
@@ -165,8 +165,9 @@ static RPCHelpMan getpeerinfo()
         [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
 {
     NodeContext& node = EnsureNodeContext(request.context);
-    if(!node.connman)
+    if(!node.connman || !node.peerman) {
         throw JSONRPCError(RPC_CLIENT_P2P_DISABLED, "Error: Peer-to-peer functionality missing or disabled");
+    }
 
     std::vector<CNodeStats> vstats;
     node.connman->GetNodeStats(vstats);
@@ -176,7 +177,7 @@ static RPCHelpMan getpeerinfo()
     for (const CNodeStats& stats : vstats) {
         UniValue obj(UniValue::VOBJ);
         CNodeStateStats statestats;
-        bool fStateStats = GetNodeStateStats(stats.nodeid, statestats);
+        bool fStateStats = node.peerman->GetNodeStateStats(stats.nodeid, statestats);
         obj.pushKV("id", stats.nodeid);
         obj.pushKV("addr", stats.addrName);
         if (stats.addrBind.IsValid()) {