Move orphan processing to ActivateBestChain

This further decouples "main" and "net" processing logic by moving
orphan processing out of the chain-connecting cs_main lock and
into its own cs_main lock, beside all of the other chain callbacks.

Once further decoupling of net and main processing logic occurs,
orphan handing should move to its own lock, out of cs_main.

Note that this will introduce a race if there are any cases where
we assume the orphan map to be consistent with the current chain
tip, however I am confident there is no such case (ATMP will fail
without DoS score in all such cases).

src/main.cpp

@@ -2461,7 +2461,6 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
 
     CCheckQueueControl<CScriptCheck> control(fScriptChecks && nScriptCheckThreads ? &scriptcheckqueue : NULL);
 
-    std::vector<uint256> vOrphanErase;
     std::vector<int> prevheights;
     CAmount nFees = 0;
     int nInputs = 0;
@@ -2492,17 +2491,6 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
                 prevheights[j] = view.AccessCoins(tx.vin[j].prevout.hash)->nHeight;
             }
 
-            // Which orphan pool entries must we evict?
-            for (size_t j = 0; j < tx.vin.size(); j++) {
-                auto itByPrev = mapOrphanTransactionsByPrev.find(tx.vin[j].prevout);
-                if (itByPrev == mapOrphanTransactionsByPrev.end()) continue;
-                for (auto mi = itByPrev->second.begin(); mi != itByPrev->second.end(); ++mi) {
-                    const CTransaction& orphanTx = (*mi)->second.tx;
-                    const uint256& orphanHash = orphanTx.GetHash();
-                    vOrphanErase.push_back(orphanHash);
-                }
-            }
-
             if (!SequenceLocks(tx, nLockTimeFlags, &prevheights, *pindex)) {
                 return state.DoS(100, error("%s: contains a non-BIP68-final transaction", __func__),
                                  REJECT_INVALID, "bad-txns-nonfinal");
@@ -2592,14 +2580,6 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
     GetMainSignals().UpdatedTransaction(hashPrevBestCoinBase);
     hashPrevBestCoinBase = block.vtx[0].GetHash();
 
-    // Erase orphan transactions include or precluded by this block
-    if (vOrphanErase.size()) {
-        int nErased = 0;
-        BOOST_FOREACH(uint256 &orphanHash, vOrphanErase) {
-            nErased += EraseOrphanTx(orphanHash);
-        }
-        LogPrint("mempool", "Erased %d orphan tx included or conflicted by block\n", nErased);
-    }
 
     int64_t nTime6 = GetTimeMicros(); nTimeCallbacks += nTime6 - nTime5;
     LogPrint("bench", "    - Callbacks: %.2fms [%.2fs]\n", 0.001 * (nTime6 - nTime5), nTimeCallbacks * 0.000001);
@@ -3105,6 +3085,33 @@ bool ActivateBestChain(CValidationState &state, const CChainParams& chainparams,
         }
         // When we reach this point, we switched to a new tip (stored in pindexNewTip).
 
+        // Remove orphan transactions with cs_main
+        {
+            LOCK(cs_main);
+            std::vector<uint256> vOrphanErase;
+            for(unsigned int i = 0; i < txChanged.size(); i++) {
+                const CTransaction& tx = std::get<0>(txChanged[i]);
+                // Which orphan pool entries must we evict?
+                for (size_t j = 0; j < tx.vin.size(); j++) {
+                    auto itByPrev = mapOrphanTransactionsByPrev.find(tx.vin[j].prevout);
+                    if (itByPrev == mapOrphanTransactionsByPrev.end()) continue;
+                    for (auto mi = itByPrev->second.begin(); mi != itByPrev->second.end(); ++mi) {
+                        const CTransaction& orphanTx = (*mi)->second.tx;
+                        const uint256& orphanHash = orphanTx.GetHash();
+                        vOrphanErase.push_back(orphanHash);
+                    }
+                }
+            }
+            // Erase orphan transactions include or precluded by this block
+            if (vOrphanErase.size()) {
+                int nErased = 0;
+                BOOST_FOREACH(uint256 &orphanHash, vOrphanErase) {
+                    nErased += EraseOrphanTx(orphanHash);
+                }
+                LogPrint("mempool", "Erased %d orphan tx included or conflicted by block\n", nErased);
+            }
+        }
+
         // Notifications/callbacks that can run without cs_main
 
         // throw all transactions though the signal-interface