tx fees, policy: periodically flush fee estimates to fee_estimates.dat

This reduces chances of having old estimates in fee_estimates.dat.

src/init.cpp

@@ -1253,7 +1253,13 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     assert(!node.fee_estimator);
     // Don't initialize fee estimation with old data if we don't relay transactions,
     // as they would never get updated.
-    if (!ignores_incoming_txs) node.fee_estimator = std::make_unique<CBlockPolicyEstimator>(FeeestPath(args));
+    if (!ignores_incoming_txs) {
+        node.fee_estimator = std::make_unique<CBlockPolicyEstimator>(FeeestPath(args));
+
+        // Flush estimates to disk periodically
+        CBlockPolicyEstimator* fee_estimator = node.fee_estimator.get();
+        node.scheduler->scheduleEvery([fee_estimator] { fee_estimator->FlushFeeEstimates(); }, FEE_FLUSH_INTERVAL);
+    }
 
     // Check port numbers
     for (const std::string port_option : {

src/policy/fees.cpp

@@ -903,10 +903,16 @@ CFeeRate CBlockPolicyEstimator::estimateSmartFee(int confTarget, FeeCalculation
 
 void CBlockPolicyEstimator::Flush() {
     FlushUnconfirmed();
+    FlushFeeEstimates();
+}
 
+void CBlockPolicyEstimator::FlushFeeEstimates()
+{
     AutoFile est_file{fsbridge::fopen(m_estimation_filepath, "wb")};
     if (est_file.IsNull() || !Write(est_file)) {
         LogPrintf("Failed to write fee estimates to %s. Continue anyway.\n", fs::PathToString(m_estimation_filepath));
+    } else {
+        LogPrintf("Flushed fee estimates to %s.\n", fs::PathToString(m_estimation_filepath.filename()));
     }
 }
 

src/policy/fees.h

@@ -14,12 +14,17 @@
 #include <util/fs.h>
 
 #include <array>
+#include <chrono>
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
 #include <vector>
 
+
+// How often to flush fee estimates to fee_estimates.dat.
+static constexpr std::chrono::hours FEE_FLUSH_INTERVAL{1};
+
 class AutoFile;
 class CTxMemPoolEntry;
 class TxConfirmStats;
@@ -239,6 +244,10 @@ public:
     void Flush()
         EXCLUSIVE_LOCKS_REQUIRED(!m_cs_fee_estimator);
 
+    /** Record current fee estimations. */
+    void FlushFeeEstimates()
+        EXCLUSIVE_LOCKS_REQUIRED(!m_cs_fee_estimator);
+
 private:
     mutable Mutex m_cs_fee_estimator;