From 714a3e6505d986d064d3a34038a724ac1cad5308 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Wed, 9 Jul 2014 18:04:18 +0200
Subject: [PATCH] Only keep setBlockIndexValid entries that are possible
 improvements

---
 src/main.cpp | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/main.cpp b/src/main.cpp
index a9c080ffaee..f8e9f163896 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -94,7 +94,9 @@ namespace {
     };
 
     CBlockIndex *pindexBestInvalid;
-    // may contain all CBlockIndex*'s that have validness >=BLOCK_VALID_TRANSACTIONS, and must contain those who aren't failed
+
+    // The set of all CBlockIndex entries with BLOCK_VALID_TRANSACTIONS or better that are at least
+    // as good as our current tip. Entries may be failed, though.
     set<CBlockIndex*, CBlockIndexWorkComparator> setBlockIndexValid;
 
     CCriticalSection cs_LastBlockFile;
@@ -2129,6 +2131,15 @@ static bool ActivateBestChainStep(CValidationState &state, CBlockIndex *pindexMo
                 return false;
             }
         } else {
+            // Delete all entries in setBlockIndexValid that are worse than our new current block.
+            // Note that we can't delete the current block itself, as we may need to return to it later in case a
+            // reorganization to a better block fails.
+            std::set<CBlockIndex*, CBlockIndexWorkComparator>::iterator it = setBlockIndexValid.begin();
+            while (setBlockIndexValid.value_comp()(*it, chainActive.Tip())) {
+                setBlockIndexValid.erase(it++);
+            }
+            // Either the current tip or a successor of it we're working towards is left in setBlockIndexValid.
+            assert(!setBlockIndexValid.empty());
             if (!pindexOldTip || chainActive.Tip()->nChainWork > pindexOldTip->nChainWork) {
                 // We're in a better position than we were. Return temporarily to release the lock.
                 break;