refactor: Make CTxMemPool::m_check_ratio a const and a constructor argument

Since m_check_ratio is only set once and since the CTxMemPool object is
no longer a global variable, m_check_ratio can be passed into the
constructor of CTxMemPool. Since it is only read from after
initialization, m_check_ratio can also be made a const and hence no
longer needs to be guarded by the cs mutex.

src/init.cpp

@@ -1389,14 +1389,9 @@ bool AppInitMain(const util::Ref& context, NodeContext& node, interfaces::BlockA
     assert(!node.connman);
     node.connman = MakeUnique<CConnman>(GetRand(std::numeric_limits<uint64_t>::max()), GetRand(std::numeric_limits<uint64_t>::max()), args.GetBoolArg("-networkactive", true));
 
-    // Make mempool generally available in the node context. For example the connection manager, wallet, or RPC threads,
-    // which are all started after this, may use it from the node context.
     assert(!node.mempool);
-    node.mempool = MakeUnique<CTxMemPool>(&::feeEstimator);
-    if (node.mempool) {
-        int check_ratio = std::min<int>(std::max<int>(args.GetArg("-checkmempool", chainparams.DefaultConsistencyChecks() ? 1 : 0), 0), 1000000);
-        node.mempool->setSanityCheck(check_ratio);
-    }
+    int check_ratio = std::min<int>(std::max<int>(args.GetArg("-checkmempool", chainparams.DefaultConsistencyChecks() ? 1 : 0), 0), 1000000);
+    node.mempool = MakeUnique<CTxMemPool>(&::feeEstimator, check_ratio);
 
     assert(!node.chainman);
     node.chainman = &g_chainman;

src/test/util/setup_common.cpp

@@ -141,8 +141,7 @@ TestingSetup::TestingSetup(const std::string& chainName, const std::vector<const
 
     pblocktree.reset(new CBlockTreeDB(1 << 20, true));
 
-    m_node.mempool = MakeUnique<CTxMemPool>(&::feeEstimator);
-    m_node.mempool->setSanityCheck(1.0);
+    m_node.mempool = MakeUnique<CTxMemPool>(&::feeEstimator, 1);
 
     m_node.chainman = &::g_chainman;
     m_node.chainman->InitializeChainstate(*m_node.mempool);

src/txmempool.cpp

@@ -331,15 +331,10 @@ void CTxMemPoolEntry::UpdateAncestorState(int64_t modifySize, CAmount modifyFee,
     assert(int(nSigOpCostWithAncestors) >= 0);
 }
 
-CTxMemPool::CTxMemPool(CBlockPolicyEstimator* estimator)
-    : nTransactionsUpdated(0), minerPolicyEstimator(estimator), m_epoch(0), m_has_epoch_guard(false)
+CTxMemPool::CTxMemPool(CBlockPolicyEstimator* estimator, int check_ratio)
+    : m_check_ratio(check_ratio), nTransactionsUpdated(0), minerPolicyEstimator(estimator), m_epoch(0), m_has_epoch_guard(false)
 {
     _clear(); //lock free clear
-
-    // Sanity checks off by default for performance, because otherwise
-    // accepting transactions becomes O(N^2) where N is the number
-    // of transactions in the pool
-    m_check_ratio = 0;
 }
 
 bool CTxMemPool::isSpent(const COutPoint& outpoint) const
@@ -619,11 +614,11 @@ static void CheckInputsAndUpdateCoins(const CTransaction& tx, CCoinsViewCache& m
 
 void CTxMemPool::check(const CCoinsViewCache *pcoins) const
 {
-    LOCK(cs);
     if (m_check_ratio == 0) return;
 
     if (GetRand(m_check_ratio) >= 1) return;
 
+    LOCK(cs);
     LogPrint(BCLog::MEMPOOL, "Checking mempool with %u transactions and %u inputs\n", (unsigned int)mapTx.size(), (unsigned int)mapNextTx.size());
 
     uint64_t checkTotal = 0;

src/txmempool.h

@@ -488,7 +488,7 @@ public:
 class CTxMemPool
 {
 private:
-    uint32_t m_check_ratio GUARDED_BY(cs); //!< Value n means that 1 times in n we check.
+    const int m_check_ratio; //!< Value n means that 1 times in n we check.
     std::atomic<unsigned int> nTransactionsUpdated; //!< Used by getblocktemplate to trigger CreateNewBlock() invocation
     CBlockPolicyEstimator* minerPolicyEstimator;
 
@@ -601,8 +601,14 @@ public:
     std::map<uint256, CAmount> mapDeltas;
 
     /** Create a new CTxMemPool.
+     * Sanity checks will be off by default for performance, because otherwise
+     * accepting transactions becomes O(N^2) where N is the number of transactions
+     * in the pool.
+     *
+     * @param[in] estimator is used to estimate appropriate transaction fees.
+     * @param[in] check_ratio is the ratio used to determine how often sanity checks will run.
      */
-    explicit CTxMemPool(CBlockPolicyEstimator* estimator = nullptr);
+    explicit CTxMemPool(CBlockPolicyEstimator* estimator = nullptr, int check_ratio = 0);
 
     /**
      * If sanity-checking is turned on, check makes sure the pool is
@@ -611,7 +617,6 @@ public:
      * check does nothing.
      */
     void check(const CCoinsViewCache *pcoins) const;
-    void setSanityCheck(int check_ratio = 0) { LOCK(cs); m_check_ratio = check_ratio; }
 
     // addUnchecked must updated state for all ancestors of a given transaction,
     // to track size/count of descendant transactions.  First version of