Merge bitcoin/bitcoin#19909: refactor: Remove unused CTxMemPool::clear() helper

fa818e103c txmempool: Remove unused clear() member function (MarcoFalke)

Pull request description:

  Seems odd to have code in Bitcoin Core that is unused.

  Moreover the function was broken (see https://github.com/bitcoin/bitcoin/pull/24145) and is brittle, as there is nothing that prevents similar bugs from re-appearing.

  Fix both issues by replacing it with C++11 member initializers.

ACKs for top commit:
  glozow:
    ACK fa818e103c

Tree-SHA512: e79e44cac7d5a84d9ecc8e3f3b0b9a50e1e3ebec358b20ba5dac175ef07d1fbe338a20f83ee80f746f7c726c79e77f8be49e14bca57a41063da8a5302123c3a9

src/test/txvalidationcache_tests.cpp

@@ -77,7 +77,9 @@ BOOST_FIXTURE_TEST_CASE(tx_mempool_block_doublespend, Dersig100Setup)
         LOCK(cs_main);
         BOOST_CHECK(m_node.chainman->ActiveChain().Tip()->GetBlockHash() != block.GetHash());
     }
-    m_node.mempool->clear();
+    BOOST_CHECK_EQUAL(m_node.mempool->size(), 1U);
+    WITH_LOCK(m_node.mempool->cs, m_node.mempool->removeRecursive(CTransaction{spends[0]}, MemPoolRemovalReason::CONFLICT));
+    BOOST_CHECK_EQUAL(m_node.mempool->size(), 0U);
 
     // Test 3: ... and should be rejected if spend2 is in the memory pool
     BOOST_CHECK(ToMemPool(spends[1]));
@@ -86,7 +88,9 @@ BOOST_FIXTURE_TEST_CASE(tx_mempool_block_doublespend, Dersig100Setup)
         LOCK(cs_main);
         BOOST_CHECK(m_node.chainman->ActiveChain().Tip()->GetBlockHash() != block.GetHash());
     }
-    m_node.mempool->clear();
+    BOOST_CHECK_EQUAL(m_node.mempool->size(), 1U);
+    WITH_LOCK(m_node.mempool->cs, m_node.mempool->removeRecursive(CTransaction{spends[1]}, MemPoolRemovalReason::CONFLICT));
+    BOOST_CHECK_EQUAL(m_node.mempool->size(), 0U);
 
     // Final sanity test: first spend in *m_node.mempool, second in block, that's OK:
     std::vector<CMutableTransaction> oneSpend;

src/txmempool.cpp

@@ -396,7 +396,6 @@ CTxMemPool::CTxMemPool(const Options& opts)
       m_full_rbf{opts.full_rbf},
       m_limits{opts.limits}
 {
-    _clear(); //lock free clear
 }
 
 bool CTxMemPool::isSpent(const COutPoint& outpoint) const
@@ -634,26 +633,6 @@ void CTxMemPool::removeForBlock(const std::vector<CTransactionRef>& vtx, unsigne
     blockSinceLastRollingFeeBump = true;
 }
 
-void CTxMemPool::_clear()
-{
-    vTxHashes.clear();
-    mapTx.clear();
-    mapNextTx.clear();
-    totalTxSize = 0;
-    m_total_fee = 0;
-    cachedInnerUsage = 0;
-    lastRollingFeeUpdate = GetTime();
-    blockSinceLastRollingFeeBump = false;
-    rollingMinimumFeeRate = 0;
-    ++nTransactionsUpdated;
-}
-
-void CTxMemPool::clear()
-{
-    LOCK(cs);
-    _clear();
-}
-
 void CTxMemPool::check(const CCoinsViewCache& active_coins_tip, int64_t spendheight) const
 {
     if (m_check_ratio == 0) return;

src/txmempool.h

@@ -319,14 +319,14 @@ protected:
     std::atomic<unsigned int> nTransactionsUpdated{0}; //!< Used by getblocktemplate to trigger CreateNewBlock() invocation
     CBlockPolicyEstimator* const minerPolicyEstimator;
 
-    uint64_t totalTxSize GUARDED_BY(cs);      //!< sum of all mempool tx's virtual sizes. Differs from serialized tx size since witness data is discounted. Defined in BIP 141.
-    CAmount m_total_fee GUARDED_BY(cs);       //!< sum of all mempool tx's fees (NOT modified fee)
-    uint64_t cachedInnerUsage GUARDED_BY(cs); //!< sum of dynamic memory usage of all the map elements (NOT the maps themselves)
+    uint64_t totalTxSize GUARDED_BY(cs){0};      //!< sum of all mempool tx's virtual sizes. Differs from serialized tx size since witness data is discounted. Defined in BIP 141.
+    CAmount m_total_fee GUARDED_BY(cs){0};       //!< sum of all mempool tx's fees (NOT modified fee)
+    uint64_t cachedInnerUsage GUARDED_BY(cs){0}; //!< sum of dynamic memory usage of all the map elements (NOT the maps themselves)
 
-    mutable int64_t lastRollingFeeUpdate GUARDED_BY(cs);
-    mutable bool blockSinceLastRollingFeeBump GUARDED_BY(cs);
-    mutable double rollingMinimumFeeRate GUARDED_BY(cs); //!< minimum fee to get into the pool, decreases exponentially
-    mutable Epoch m_epoch GUARDED_BY(cs);
+    mutable int64_t lastRollingFeeUpdate GUARDED_BY(cs){GetTime()};
+    mutable bool blockSinceLastRollingFeeBump GUARDED_BY(cs){false};
+    mutable double rollingMinimumFeeRate GUARDED_BY(cs){0}; //!< minimum fee to get into the pool, decreases exponentially
+    mutable Epoch m_epoch GUARDED_BY(cs){};
 
     // In-memory counter for external mempool tracking purposes.
     // This number is incremented once every time a transaction
@@ -500,8 +500,6 @@ public:
     void removeConflicts(const CTransaction& tx) EXCLUSIVE_LOCKS_REQUIRED(cs);
     void removeForBlock(const std::vector<CTransactionRef>& vtx, unsigned int nBlockHeight) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
-    void clear();
-    void _clear() EXCLUSIVE_LOCKS_REQUIRED(cs); //lock free
     bool CompareDepthAndScore(const uint256& hasha, const uint256& hashb, bool wtxid=false);
     void queryHashes(std::vector<uint256>& vtxid) const;
     bool isSpent(const COutPoint& outpoint) const;