From 072e2f864445bc6ef3b390255f08c9e8bec2ea94 Mon Sep 17 00:00:00 2001
From: Alex Morcos <morcos@chaincode.com>
Date: Thu, 26 Mar 2015 13:52:10 -0400
Subject: [PATCH] Alter assumptions in CCoinsViewCache::BatchWrite

Previously it would break if you flushed a parent cache while there was a child cache referring to it.  This change will allow the flushing of parent caches.
---
 src/coins.cpp            | 19 ++++++++++++-------
 src/test/coins_tests.cpp | 16 ++++++++++++++++
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/src/coins.cpp b/src/coins.cpp
index 96b336ce7..f0ea5c045 100644
--- a/src/coins.cpp
+++ b/src/coins.cpp
@@ -160,18 +160,23 @@ bool CCoinsViewCache::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlockIn
         if (it->second.flags & CCoinsCacheEntry::DIRTY) { // Ignore non-dirty entries (optimization).
             CCoinsMap::iterator itUs = cacheCoins.find(it->first);
             if (itUs == cacheCoins.end()) {
-                if (!it->second.coins.IsPruned()) {
-                    // The parent cache does not have an entry, while the child
-                    // cache does have (a non-pruned) one. Move the data up, and
-                    // mark it as fresh (if the grandparent did have it, we
-                    // would have pulled it in at first GetCoins).
-                    assert(it->second.flags & CCoinsCacheEntry::FRESH);
+                // The parent cache does not have an entry, while the child does
+                // We can ignore it if it's both FRESH and pruned in the child
+                if (!(it->second.flags & CCoinsCacheEntry::FRESH && it->second.coins.IsPruned())) {
+                    // Otherwise we will need to create it in the parent
+                    // and move the data up and mark it as dirty
                     CCoinsCacheEntry& entry = cacheCoins[it->first];
                     entry.coins.swap(it->second.coins);
                     cachedCoinsUsage += entry.coins.DynamicMemoryUsage();
-                    entry.flags = CCoinsCacheEntry::DIRTY | CCoinsCacheEntry::FRESH;
+                    entry.flags = CCoinsCacheEntry::DIRTY;
+                    // We can mark it FRESH in the parent if it was FRESH in the child
+                    // Otherwise it might have just been flushed from the parent's cache
+                    // and already exist in the grandparent
+                    if (it->second.flags & CCoinsCacheEntry::FRESH)
+                        entry.flags |= CCoinsCacheEntry::FRESH;
                 }
             } else {
+                // Found the entry in the parent cache
                 if ((itUs->second.flags & CCoinsCacheEntry::FRESH) && it->second.coins.IsPruned()) {
                     // The grandparent does not have an entry, and the child is
                     // modified and being pruned. This means we can just delete
diff --git a/src/test/coins_tests.cpp b/src/test/coins_tests.cpp
index 946f904df..9489a19f6 100644
--- a/src/test/coins_tests.cpp
+++ b/src/test/coins_tests.cpp
@@ -164,14 +164,23 @@ BOOST_AUTO_TEST_CASE(coins_cache_simulation_test)
             }
         }
 
+        if (insecure_rand() % 100 == 0) {
+            // Every 100 iterations, flush an intermediate cache
+            if (stack.size() > 1 && insecure_rand() % 2 == 0) {
+                unsigned int flushIndex = insecure_rand() % (stack.size() - 1);
+                stack[flushIndex]->Flush();
+            }
+        }
         if (insecure_rand() % 100 == 0) {
             // Every 100 iterations, change the cache stack.
             if (stack.size() > 0 && insecure_rand() % 2 == 0) {
+                //Remove the top cache
                 stack.back()->Flush();
                 delete stack.back();
                 stack.pop_back();
             }
             if (stack.size() == 0 || (stack.size() < 4 && insecure_rand() % 2)) {
+                //Add a new cache
                 CCoinsView* tip = &base;
                 if (stack.size() > 0) {
                     tip = stack.back();
@@ -304,6 +313,13 @@ BOOST_AUTO_TEST_CASE(updatecoins_simulation_test)
             }
         }
 
+        if (insecure_rand() % 100 == 0) {
+            // Every 100 iterations, flush an intermediate cache
+            if (stack.size() > 1 && insecure_rand() % 2 == 0) {
+                unsigned int flushIndex = insecure_rand() % (stack.size() - 1);
+                stack[flushIndex]->Flush();
+            }
+        }
         if (insecure_rand() % 100 == 0) {
             // Every 100 iterations, change the cache stack.
             if (stack.size() > 0 && insecure_rand() % 2 == 0) {