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

fad1f0fd33e5e7a65b702237c7ca8e1b694852d2 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 fad1f0fd33e5e7a65b702237c7ca8e1b694852d2
  practicalswift:
    cr ACK fad1f0fd33e5e7a65b702237c7ca8e1b694852d2: patch looks correct

Tree-SHA512: 647f9b954fbf52e138d3e710937eb9131b390fef0deae03fd6a162d5a18b9f194010800bbddc8f89208d91be2802dff11c3884d04b3dd233865abd12aa3cde06

3 files changed, 4 insertions, 15 deletions

diff --git a/src/net.cpp b/src/net.cpp
index 31960664e3..59835c37fc 100644
--- a/src/net.cpp
+++ b/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;
diff --git a/src/net.h b/src/net.h
index 357b4cc40d..84b5204f14 100644
--- a/src/net.h
+++ b/src/net.h
@@ -565,9 +565,8 @@ public:
         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};
     };
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index dc9b051ddd..8f1cb952f2 100644
--- a/src/net_processing.cpp
+++ b/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);