Get the set of now-uncacheable-txn from CTxMemPool::TrimToSize

src/txmempool.cpp

@@ -944,7 +944,7 @@ void CTxMemPool::trackPackageRemoved(const CFeeRate& rate) {
     }
 }
 
-void CTxMemPool::TrimToSize(size_t sizelimit) {
+void CTxMemPool::TrimToSize(size_t sizelimit, std::vector<uint256>* pvNoSpendsRemaining) {
     LOCK(cs);
 
     unsigned nTxnRemoved = 0;
@@ -963,8 +963,26 @@ void CTxMemPool::TrimToSize(size_t sizelimit) {
 
         setEntries stage;
         CalculateDescendants(mapTx.project<0>(it), stage);
-        RemoveStaged(stage);
         nTxnRemoved += stage.size();
+
+        std::vector<CTransaction> txn;
+        if (pvNoSpendsRemaining) {
+            txn.reserve(stage.size());
+            BOOST_FOREACH(txiter it, stage)
+                txn.push_back(it->GetTx());
+        }
+        RemoveStaged(stage);
+        if (pvNoSpendsRemaining) {
+            BOOST_FOREACH(const CTransaction& tx, txn) {
+                BOOST_FOREACH(const CTxIn& txin, tx.vin) {
+                    if (exists(txin.prevout.hash))
+                        continue;
+                    std::map<COutPoint, CInPoint>::iterator it = mapNextTx.lower_bound(COutPoint(txin.prevout.hash, 0));
+                    if (it == mapNextTx.end() || it->first.hash != txin.prevout.hash)
+                        pvNoSpendsRemaining->push_back(txin.prevout.hash);
+                }
+            }
+        }
     }
 
     if (maxFeeRateRemoved > CFeeRate(0))

src/txmempool.h

@@ -483,8 +483,11 @@ public:
       */
     CFeeRate GetMinFee(size_t sizelimit) const;
 
-    /** Remove transactions from the mempool until its dynamic size is <= sizelimit. */
-    void TrimToSize(size_t sizelimit);
+    /** Remove transactions from the mempool until its dynamic size is <= sizelimit.
+      *  pvNoSpendsRemaining, if set, will be populated with the list of transactions
+      *  which are not in mempool which no longer have any spends in this mempool.
+      */
+    void TrimToSize(size_t sizelimit, std::vector<uint256>* pvNoSpendsRemaining=NULL);
 
     /** Expire all transaction (and their dependencies) in the mempool older than time. Return the number of removed transactions. */
     int Expire(int64_t time);