Merge #9371: Notify on removal

094e4b3 Better document usage of SyncTransaction (Alex Morcos)
4afbde6 Introduce MemPoolConflictRemovalTracker (Alex Morcos)
ff25c32 mempool: add notification for added/removed entries (Wladimir J. van der Laan)

src/txmempool.cpp

@@ -393,6 +393,7 @@ void CTxMemPool::AddTransactionsUpdated(unsigned int n)
 
 bool CTxMemPool::addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry, setEntries &setAncestors, bool validFeeEstimate)
 {
+    NotifyEntryAdded(entry.GetSharedTx());
     // Add to memory pool without checking anything.
     // Used by main.cpp AcceptToMemoryPool(), which DOES do
     // all the appropriate checks.
@@ -449,8 +450,9 @@ bool CTxMemPool::addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry,
     return true;
 }
 
-void CTxMemPool::removeUnchecked(txiter it)
+void CTxMemPool::removeUnchecked(txiter it, MemPoolRemovalReason reason)
 {
+    NotifyEntryRemoved(it->GetSharedTx(), reason);
     const uint256 hash = it->GetTx().GetHash();
     BOOST_FOREACH(const CTxIn& txin, it->GetTx().vin)
         mapNextTx.erase(txin.prevout);
@@ -502,7 +504,7 @@ void CTxMemPool::CalculateDescendants(txiter entryit, setEntries &setDescendants
     }
 }
 
-void CTxMemPool::removeRecursive(const CTransaction &origTx)
+void CTxMemPool::removeRecursive(const CTransaction &origTx, MemPoolRemovalReason reason)
 {
     // Remove transaction from memory pool
     {
@@ -529,7 +531,8 @@ void CTxMemPool::removeRecursive(const CTransaction &origTx)
         BOOST_FOREACH(txiter it, txToRemove) {
             CalculateDescendants(it, setAllRemoves);
         }
-        RemoveStaged(setAllRemoves, false);
+
+        RemoveStaged(setAllRemoves, false, reason);
     }
 }
 
@@ -567,7 +570,7 @@ void CTxMemPool::removeForReorg(const CCoinsViewCache *pcoins, unsigned int nMem
     for (txiter it : txToRemove) {
         CalculateDescendants(it, setAllRemoves);
     }
-    RemoveStaged(setAllRemoves, false);
+    RemoveStaged(setAllRemoves, false, MemPoolRemovalReason::REORG);
 }
 
 void CTxMemPool::removeConflicts(const CTransaction &tx)
@@ -581,7 +584,7 @@ void CTxMemPool::removeConflicts(const CTransaction &tx)
             if (txConflict != tx)
             {
                 ClearPrioritisation(txConflict.GetHash());
-                removeRecursive(txConflict);
+                removeRecursive(txConflict, MemPoolRemovalReason::CONFLICT);
             }
         }
     }
@@ -610,7 +613,7 @@ void CTxMemPool::removeForBlock(const std::vector<CTransactionRef>& vtx, unsigne
         if (it != mapTx.end()) {
             setEntries stage;
             stage.insert(it);
-            RemoveStaged(stage, true);
+            RemoveStaged(stage, true, MemPoolRemovalReason::BLOCK);
         }
         removeConflicts(*tx);
         ClearPrioritisation(tx->GetHash());
@@ -989,11 +992,11 @@ size_t CTxMemPool::DynamicMemoryUsage() const {
     return memusage::MallocUsage(sizeof(CTxMemPoolEntry) + 15 * sizeof(void*)) * mapTx.size() + memusage::DynamicUsage(mapNextTx) + memusage::DynamicUsage(mapDeltas) + memusage::DynamicUsage(mapLinks) + memusage::DynamicUsage(vTxHashes) + cachedInnerUsage;
 }
 
-void CTxMemPool::RemoveStaged(setEntries &stage, bool updateDescendants) {
+void CTxMemPool::RemoveStaged(setEntries &stage, bool updateDescendants, MemPoolRemovalReason reason) {
     AssertLockHeld(cs);
     UpdateForRemoveFromMempool(stage, updateDescendants);
     BOOST_FOREACH(const txiter& it, stage) {
-        removeUnchecked(it);
+        removeUnchecked(it, reason);
     }
 }
 
@@ -1009,7 +1012,7 @@ int CTxMemPool::Expire(int64_t time) {
     BOOST_FOREACH(txiter removeit, toremove) {
         CalculateDescendants(removeit, stage);
     }
-    RemoveStaged(stage, false);
+    RemoveStaged(stage, false, MemPoolRemovalReason::EXPIRY);
     return stage.size();
 }
 
@@ -1118,7 +1121,7 @@ void CTxMemPool::TrimToSize(size_t sizelimit, std::vector<uint256>* pvNoSpendsRe
             BOOST_FOREACH(txiter iter, stage)
                 txn.push_back(iter->GetTx());
         }
-        RemoveStaged(stage, false);
+        RemoveStaged(stage, false, MemPoolRemovalReason::SIZELIMIT);
         if (pvNoSpendsRemaining) {
             BOOST_FOREACH(const CTransaction& tx, txn) {
                 BOOST_FOREACH(const CTxIn& txin, tx.vin) {

src/txmempool.h

@@ -25,6 +25,8 @@
 #include "boost/multi_index/ordered_index.hpp"
 #include "boost/multi_index/hashed_index.hpp"
 
+#include <boost/signals2/signal.hpp>
+
 class CAutoFile;
 class CBlockIndex;
 
@@ -333,6 +335,19 @@ struct TxMempoolInfo
     int64_t nFeeDelta;
 };
 
+/** Reason why a transaction was removed from the mempool,
+ * this is passed to the notification signal.
+ */
+enum class MemPoolRemovalReason {
+    UNKNOWN = 0, //! Manually removed or unknown reason
+    EXPIRY,      //! Expired from mempool
+    SIZELIMIT,   //! Removed in size limiting
+    REORG,       //! Removed for reorganization
+    BLOCK,       //! Removed for block
+    CONFLICT,    //! Removed for conflict with in-block transaction
+    REPLACED     //! Removed for replacement
+};
+
 /**
  * CTxMemPool stores valid-according-to-the-current-best-chain transactions
  * that may be included in the next block.
@@ -521,10 +536,11 @@ public:
     bool addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry, bool validFeeEstimate = true);
     bool addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry, setEntries &setAncestors, bool validFeeEstimate = true);
 
-    void removeRecursive(const CTransaction &tx);
+    void removeRecursive(const CTransaction &tx, MemPoolRemovalReason reason = MemPoolRemovalReason::UNKNOWN);
     void removeForReorg(const CCoinsViewCache *pcoins, unsigned int nMemPoolHeight, int flags);
     void removeConflicts(const CTransaction &tx);
     void removeForBlock(const std::vector<CTransactionRef>& vtx, unsigned int nBlockHeight);
+
     void clear();
     void _clear(); //lock free
     bool CompareDepthAndScore(const uint256& hasha, const uint256& hashb);
@@ -551,7 +567,7 @@ public:
      *  Set updateDescendants to true when removing a tx that was in a block, so
      *  that any in-mempool descendants have their ancestor state updated.
      */
-    void RemoveStaged(setEntries &stage, bool updateDescendants);
+    void RemoveStaged(setEntries &stage, bool updateDescendants, MemPoolRemovalReason reason = MemPoolRemovalReason::UNKNOWN);
 
     /** When adding transactions from a disconnected block back to the mempool,
      *  new mempool entries may have children in the mempool (which is generally
@@ -647,6 +663,9 @@ public:
 
     size_t DynamicMemoryUsage() const;
 
+    boost::signals2::signal<void (CTransactionRef)> NotifyEntryAdded;
+    boost::signals2::signal<void (CTransactionRef, MemPoolRemovalReason)> NotifyEntryRemoved;
+
 private:
     /** UpdateForDescendants is used by UpdateTransactionsFromBlock to update
      *  the descendants for a single transaction that has been added to the
@@ -683,7 +702,7 @@ private:
      *  transactions in a chain before we've updated all the state for the
      *  removal.
      */
-    void removeUnchecked(txiter entry);
+    void removeUnchecked(txiter entry, MemPoolRemovalReason reason = MemPoolRemovalReason::UNKNOWN);
 };
 
 /** 

src/validation.cpp

@@ -157,6 +157,39 @@ namespace {
     set<int> setDirtyFileInfo;
 } // anon namespace
 
+/* Use this class to start tracking transactions that are removed from the
+ * mempool and pass all those transactions through SyncTransaction when the
+ * object goes out of scope. This is currently only used to call SyncTransaction
+ * on conflicts removed from the mempool during block connection.  Applied in
+ * ActivateBestChain around ActivateBestStep which in turn calls:
+ * ConnectTip->removeForBlock->removeConflicts
+ */
+class MemPoolConflictRemovalTracker
+{
+private:
+    std::vector<CTransactionRef> conflictedTxs;
+    CTxMemPool &pool;
+
+public:
+    MemPoolConflictRemovalTracker(CTxMemPool &_pool) : pool(_pool) {
+        pool.NotifyEntryRemoved.connect(boost::bind(&MemPoolConflictRemovalTracker::NotifyEntryRemoved, this, _1, _2));
+    }
+
+    void NotifyEntryRemoved(CTransactionRef txRemoved, MemPoolRemovalReason reason) {
+        if (reason == MemPoolRemovalReason::CONFLICT) {
+            conflictedTxs.push_back(txRemoved);
+        }
+    }
+
+    ~MemPoolConflictRemovalTracker() {
+        pool.NotifyEntryRemoved.disconnect(boost::bind(&MemPoolConflictRemovalTracker::NotifyEntryRemoved, this, _1, _2));
+        for (const auto& tx : conflictedTxs) {
+            GetMainSignals().SyncTransaction(*tx, NULL, CMainSignals::SYNC_TRANSACTION_NOT_IN_BLOCK);
+        }
+        conflictedTxs.clear();
+    }
+};
+
 CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& locator)
 {
     // Find the first block the caller has in the main chain
@@ -956,7 +989,7 @@ bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState& state, const C
             if (plTxnReplaced)
                 plTxnReplaced->push_back(it->GetSharedTx());
         }
-        pool.RemoveStaged(allConflicting, false);
+        pool.RemoveStaged(allConflicting, false, MemPoolRemovalReason::REPLACED);
 
         // This transaction should only count for fee estimation if
         // the node is not behind and it is not dependent on any other
@@ -2166,7 +2199,7 @@ bool static DisconnectTip(CValidationState& state, const CChainParams& chainpara
             // ignore validation errors in resurrected transactions
             CValidationState stateDummy;
             if (tx.IsCoinBase() || !AcceptToMemoryPool(mempool, stateDummy, it, false, NULL, NULL, true)) {
-                mempool.removeRecursive(tx);
+                mempool.removeRecursive(tx, MemPoolRemovalReason::REORG);
             } else if (mempool.exists(tx.GetHash())) {
                 vHashUpdate.push_back(tx.GetHash());
             }
@@ -2453,6 +2486,14 @@ bool ActivateBestChain(CValidationState &state, const CChainParams& chainparams,
         bool fInitialDownload;
         {
             LOCK(cs_main);
+            { // TODO: Tempoarily ensure that mempool removals are notified before
+              // connected transactions.  This shouldn't matter, but the abandoned
+              // state of transactions in our wallet is currently cleared when we
+              // receive another notification and there is a race condition where
+              // notification of a connected conflict might cause an outside process
+              // to abandon a transaction and then have it inadvertantly cleared by
+              // the notification that the conflicted transaction was evicted.
+            MemPoolConflictRemovalTracker mrt(mempool);
             CBlockIndex *pindexOldTip = chainActive.Tip();
             if (pindexMostWork == NULL) {
                 pindexMostWork = FindMostWorkChain();
@@ -2476,6 +2517,10 @@ bool ActivateBestChain(CValidationState &state, const CChainParams& chainparams,
             fInitialDownload = IsInitialBlockDownload();
 
             // throw all transactions though the signal-interface
+
+            } // MemPoolConflictRemovalTracker destroyed and conflict evictions are notified
+
+            // Transactions in the connnected block are notified
             for (const auto& pair : connectTrace.blocksConnected) {
                 assert(pair.second);
                 const CBlock& block = *(pair.second);

src/validationinterface.h

@@ -50,9 +50,16 @@ protected:
 struct CMainSignals {
     /** Notifies listeners of updated block chain tip */
     boost::signals2::signal<void (const CBlockIndex *, const CBlockIndex *, bool fInitialDownload)> UpdatedBlockTip;
-    /** A posInBlock value for SyncTransaction which indicates the transaction was conflicted, disconnected, or not in a block */
+    /** A posInBlock value for SyncTransaction calls for tranactions not
+     * included in connected blocks such as transactions removed from mempool,
+     * accepted to mempool or appearing in disconnected blocks.*/
     static const int SYNC_TRANSACTION_NOT_IN_BLOCK = -1;
-    /** Notifies listeners of updated transaction data (transaction, and optionally the block it is found in. */
+    /** Notifies listeners of updated transaction data (transaction, and
+     * optionally the block it is found in). Called with block data when
+     * transaction is included in a connected block, and without block data when
+     * transaction was accepted to mempool, removed from mempool (only when
+     * removal was due to conflict from connected block), or appeared in a
+     * disconnected block.*/
     boost::signals2::signal<void (const CTransaction &, const CBlockIndex *pindex, int posInBlock)> SyncTransaction;
     /** Notifies listeners of an updated transaction without new data (for now: a coinbase potentially becoming visible). */
     boost::signals2::signal<void (const uint256 &)> UpdatedTransaction;

src/wallet/wallet.cpp

@@ -1003,9 +1003,17 @@ bool CWallet::LoadToWallet(const CWalletTx& wtxIn)
 }
 
 /**
- * Add a transaction to the wallet, or update it.
- * pblock is optional, but should be provided if the transaction is known to be in a block.
+ * Add a transaction to the wallet, or update it.  pIndex and posInBlock should
+ * be set when the transaction was known to be included in a block.  When
+ * posInBlock = SYNC_TRANSACTION_NOT_IN_BLOCK (-1) , then wallet state is not
+ * updated in AddToWallet, but notifications happen and cached balances are
+ * marked dirty.
  * If fUpdate is true, existing transactions will be updated.
+ * TODO: One exception to this is that the abandoned state is cleared under the
+ * assumption that any further notification of a transaction that was considered
+ * abandoned is an indication that it is not safe to be considered abandoned.
+ * Abandoned state should probably be more carefuly tracked via different
+ * posInBlock signals or by checking mempool presence when necessary.
  */
 bool CWallet::AddToWalletIfInvolvingMe(const CTransaction& tx, const CBlockIndex* pIndex, int posInBlock, bool fUpdate)
 {