CValidationInterface: add new callback `MempoolTransactionsRemovedFor…

…ConnectedBlock`

`MempoolTransactionsRemovedForConnectedBlock` notifies listeners
of the txs that are removed from the mempool because a new block is connected.

It also returns the block height the txs were confirmed.

Co-authored-by: Matt Corallo <git@bluematt.me>

src/txmempool.cpp

@@ -649,17 +649,21 @@ void CTxMemPool::removeForBlock(const std::vector<CTransactionRef>& vtx, unsigne
     }
     // Before the txs in the new block have been removed from the mempool, update policy estimates
     if (minerPolicyEstimator) {minerPolicyEstimator->processBlock(nBlockHeight, entries);}
+    std::vector<CTransactionRef> txs_removed_for_block;
+    txs_removed_for_block.reserve(vtx.size());
     for (const auto& tx : vtx)
     {
         txiter it = mapTx.find(tx->GetHash());
         if (it != mapTx.end()) {
             setEntries stage;
             stage.insert(it);
+            txs_removed_for_block.push_back(tx);
             RemoveStaged(stage, true, MemPoolRemovalReason::BLOCK);
         }
         removeConflicts(*tx);
         ClearPrioritisation(tx->GetHash());
     }
+    GetMainSignals().MempoolTransactionsRemovedForConnectedBlock(txs_removed_for_block, nBlockHeight);
     lastRollingFeeUpdate = GetTime();
     blockSinceLastRollingFeeBump = true;
 }

src/validationinterface.cpp

@@ -214,6 +214,16 @@ void CMainSignals::TransactionAddedToMempool(const CTransactionRef& tx, uint64_t
                           tx->GetWitnessHash().ToString());
 }
 
+void CMainSignals::MempoolTransactionsRemovedForConnectedBlock(const std::vector<CTransactionRef>& txs_removed_for_block, unsigned int nBlockHeight)
+{
+    auto event = [txs_removed_for_block, nBlockHeight, this] {
+        m_internals->Iterate([&](CValidationInterface& callbacks) { callbacks.MempoolTransactionsRemovedForConnectedBlock(txs_removed_for_block, nBlockHeight); });
+    };
+    ENQUEUE_AND_LOG_EVENT(event, "%s: block height=%s txs=%s", __func__,
+                          nBlockHeight,
+                          txs_removed_for_block.size());
+}
+
 void CMainSignals::TransactionRemovedFromMempool(const CTransactionRef& tx, MemPoolRemovalReason reason, uint64_t mempool_sequence) {
     auto event = [tx, reason, mempool_sequence, this] {
         m_internals->Iterate([&](CValidationInterface& callbacks) { callbacks.TransactionRemovedFromMempool(tx, reason, mempool_sequence); });

src/validationinterface.h

@@ -60,10 +60,10 @@ void CallFunctionInValidationInterfaceQueue(std::function<void ()> func);
 void SyncWithValidationInterfaceQueue() LOCKS_EXCLUDED(cs_main);
 
 /**
- * Implement this to subscribe to events generated in validation
+ * Implement this to subscribe to events generated in validation and mempool
  *
  * Each CValidationInterface() subscriber will receive event callbacks
- * in the order in which the events were generated by validation.
+ * in the order in which the events were generated by validation and mempool.
  * Furthermore, each ValidationInterface() subscriber may assume that
  * callbacks effectively run in a single thread with single-threaded
  * memory consistency. That is, for a given ValidationInterface()
@@ -113,7 +113,7 @@ class CValidationInterface {
      * This does not fire for transactions that are removed from the mempool
      * because they have been included in a block. Any client that is interested
      * in transactions removed from the mempool for inclusion in a block can learn
-     * about those transactions from the BlockConnected notification.
+     * about those transactions from the MempoolTransactionsRemovedForConnectedBlock notification.
      *
      * Transactions that are removed from the mempool because they conflict
      * with a transaction in the new block will have
@@ -131,9 +131,18 @@ class CValidationInterface {
      * Called on a background thread.
      */
     virtual void TransactionRemovedFromMempool(const CTransactionRef& tx, MemPoolRemovalReason reason, uint64_t mempool_sequence) {}
+    /* Notifies listeners of transactions removed from the mempool as
+     * as a result of new block being connected.
+     * MempoolTransactionsRemovedForConnectedBlock will be fired before BlockConnected.
+     *
+     * Called on a background thread.
+     */
+    virtual void MempoolTransactionsRemovedForConnectedBlock(const std::vector<CTransactionRef>& txs_removed_for_block, unsigned int nBlockHeight) {}
     /**
      * Notifies listeners of a block being connected.
-     * Provides a vector of transactions evicted from the mempool as a result.
+     * Provides the block that was connected.
+     * The block contains a vector of transactions from the new block,
+     * some of the transactions in the vector may not be in our mempool.
      *
      * Called on a background thread.
      */
@@ -202,6 +211,7 @@ class CMainSignals {
     void UpdatedBlockTip(const CBlockIndex *, const CBlockIndex *, bool fInitialDownload);
     void TransactionAddedToMempool(const CTransactionRef&, uint64_t mempool_sequence);
     void TransactionRemovedFromMempool(const CTransactionRef&, MemPoolRemovalReason, uint64_t mempool_sequence);
+    void MempoolTransactionsRemovedForConnectedBlock(const std::vector<CTransactionRef>&, unsigned int nBlockHeight);
     void BlockConnected(ChainstateRole, const std::shared_ptr<const CBlock> &, const CBlockIndex *pindex);
     void BlockDisconnected(const std::shared_ptr<const CBlock> &, const CBlockIndex* pindex);
     void ChainStateFlushed(ChainstateRole, const CBlockLocator &);