Merge #18819: net: Replace cs_feeFilter with simple std::atomic

fad1f0f net: Remove unused cs_feeFilter (MarcoFalke)

Pull request description:

  A `RecursiveMutex` is overkill for setting or reading a plain integer. Even a `Mutex` is overkill, when a plain `std::atomic` can be used.

  This removes 11 lines of code. Also, it is cutting down on the number of locks put on the stack at the same time, which complicates review looking out for potential lock contention.

ACKs for top commit:
  jnewbery:
    utACK fad1f0f
  practicalswift:
    cr ACK fad1f0f: patch looks correct

Tree-SHA512: 647f9b954fbf52e138d3e710937eb9131b390fef0deae03fd6a162d5a18b9f194010800bbddc8f89208d91be2802dff11c3884d04b3dd233865abd12aa3cde06

Author: fanquake

src/net.cpp

@@ -592,7 +592,6 @@ void CNode::copyStats(CNodeStats &stats, const std::vector<bool> &m_asmap)
     }
     X(m_permissionFlags);
     if (m_tx_relay != nullptr) {
-        LOCK(m_tx_relay->cs_feeFilter);
         stats.minFeeFilter = m_tx_relay->minFeeFilter;
     } else {
         stats.minFeeFilter = 0;

src/net.h

@@ -565,9 +565,8 @@ class CNode
         std::atomic<std::chrono::seconds> m_last_mempool_req{0s};
         std::chrono::microseconds nNextInvSend{0};
 
-        RecursiveMutex cs_feeFilter;
-        // Minimum fee rate with which to filter inv's to this node
-        CAmount minFeeFilter GUARDED_BY(cs_feeFilter){0};
+        /** Minimum fee rate with which to filter inv's to this node */
+        std::atomic<CAmount> minFeeFilter{0};
         CAmount lastSentFeeFilter{0};
         int64_t nextSendTimeFeeFilter{0};
     };

src/net_processing.cpp

@@ -3712,7 +3712,6 @@ void PeerManager::ProcessMessage(CNode& pfrom, const std::string& msg_type, CDat
         vRecv >> newFeeFilter;
         if (MoneyRange(newFeeFilter)) {
             if (pfrom.m_tx_relay != nullptr) {
-                LOCK(pfrom.m_tx_relay->cs_feeFilter);
                 pfrom.m_tx_relay->minFeeFilter = newFeeFilter;
             }
             LogPrint(BCLog::NET, "received: feefilter of %s from peer=%d\n", CFeeRate(newFeeFilter).ToString(), pfrom.GetId());
@@ -4388,11 +4387,7 @@ bool PeerManager::SendMessages(CNode* pto)
                 if (fSendTrickle && pto->m_tx_relay->fSendMempool) {
                     auto vtxinfo = m_mempool.infoAll();
                     pto->m_tx_relay->fSendMempool = false;
-                    CFeeRate filterrate;
-                    {
-                        LOCK(pto->m_tx_relay->cs_feeFilter);
-                        filterrate = CFeeRate(pto->m_tx_relay->minFeeFilter);
-                    }
+                    const CFeeRate filterrate{pto->m_tx_relay->minFeeFilter.load()};
 
                     LOCK(pto->m_tx_relay->cs_filter);
 
@@ -4426,11 +4421,7 @@ bool PeerManager::SendMessages(CNode* pto)
                     for (std::set<uint256>::iterator it = pto->m_tx_relay->setInventoryTxToSend.begin(); it != pto->m_tx_relay->setInventoryTxToSend.end(); it++) {
                         vInvTx.push_back(it);
                     }
-                    CFeeRate filterrate;
-                    {
-                        LOCK(pto->m_tx_relay->cs_feeFilter);
-                        filterrate = CFeeRate(pto->m_tx_relay->minFeeFilter);
-                    }
+                    const CFeeRate filterrate{pto->m_tx_relay->minFeeFilter.load()};
                     // Topologically and fee-rate sort the inventory we send for privacy and priority reasons.
                     // A heap is used so that not all items need sorting if only a few are being sent.
                     CompareInvMempoolOrder compareInvMempoolOrder(&m_mempool, state.m_wtxid_relay);