Merge pull request #4834

7c70438 Get rid of the dummy CCoinsViewCache constructor arg (Pieter Wuille)
ed27e53 Add coins_tests with a large randomized CCoinViewCache test. (Pieter Wuille)
058b08c Do not keep fully spent but unwritten CCoins entries cached. (Pieter Wuille)
c9d1a81 Get rid of CCoinsView's SetCoins and SetBestBlock. (Pieter Wuille)
f28aec0 Use ModifyCoins instead of mutable GetCoins. (Pieter Wuille)

1 files changed, 80 insertions, 37 deletions

diff --git a/src/coins.cpp b/src/coins.cpp
index 9b8d63d4e4..e4f3e67aeb 100644
--- a/src/coins.cpp
+++ b/src/coins.cpp
@@ -53,61 +53,72 @@ bool CCoins::Spend(int nPos) {
 
 
 bool CCoinsView::GetCoins(const uint256 &txid, CCoins &coins) const { return false; }
-bool CCoinsView::SetCoins(const uint256 &txid, const CCoins &coins) { return false; }
 bool CCoinsView::HaveCoins(const uint256 &txid) const { return false; }
 uint256 CCoinsView::GetBestBlock() const { return uint256(0); }
-bool CCoinsView::SetBestBlock(const uint256 &hashBlock) { return false; }
 bool CCoinsView::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) { return false; }
 bool CCoinsView::GetStats(CCoinsStats &stats) const { return false; }
 
 
-CCoinsViewBacked::CCoinsViewBacked(CCoinsView &viewIn) : base(&viewIn) { }
+CCoinsViewBacked::CCoinsViewBacked(CCoinsView *viewIn) : base(viewIn) { }
 bool CCoinsViewBacked::GetCoins(const uint256 &txid, CCoins &coins) const { return base->GetCoins(txid, coins); }
-bool CCoinsViewBacked::SetCoins(const uint256 &txid, const CCoins &coins) { return base->SetCoins(txid, coins); }
 bool CCoinsViewBacked::HaveCoins(const uint256 &txid) const { return base->HaveCoins(txid); }
 uint256 CCoinsViewBacked::GetBestBlock() const { return base->GetBestBlock(); }
-bool CCoinsViewBacked::SetBestBlock(const uint256 &hashBlock) { return base->SetBestBlock(hashBlock); }
 void CCoinsViewBacked::SetBackend(CCoinsView &viewIn) { base = &viewIn; }
 bool CCoinsViewBacked::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) { return base->BatchWrite(mapCoins, hashBlock); }
 bool CCoinsViewBacked::GetStats(CCoinsStats &stats) const { return base->GetStats(stats); }
 
 CCoinsKeyHasher::CCoinsKeyHasher() : salt(GetRandHash()) {}
 
-CCoinsViewCache::CCoinsViewCache(CCoinsView &baseIn, bool fDummy) : CCoinsViewBacked(baseIn), hashBlock(0) { }
+CCoinsViewCache::CCoinsViewCache(CCoinsView *baseIn) : CCoinsViewBacked(baseIn), hasModifier(false), hashBlock(0) { }
 
-bool CCoinsViewCache::GetCoins(const uint256 &txid, CCoins &coins) const {
-    if (cacheCoins.count(txid)) {
-        coins = cacheCoins[txid];
-        return true;
-    }
-    if (base->GetCoins(txid, coins)) {
-        cacheCoins[txid] = coins;
-        return true;
-    }
-    return false;
+CCoinsViewCache::~CCoinsViewCache()
+{
+    assert(!hasModifier);
 }
 
-CCoinsMap::iterator CCoinsViewCache::FetchCoins(const uint256 &txid) {
+CCoinsMap::const_iterator CCoinsViewCache::FetchCoins(const uint256 &txid) const {
     CCoinsMap::iterator it = cacheCoins.find(txid);
     if (it != cacheCoins.end())
         return it;
     CCoins tmp;
-    if (!base->GetCoins(txid,tmp))
+    if (!base->GetCoins(txid, tmp))
         return cacheCoins.end();
-    CCoinsMap::iterator ret = cacheCoins.insert(it, std::make_pair(txid, CCoins()));
-    tmp.swap(ret->second);
+    CCoinsMap::iterator ret = cacheCoins.insert(std::make_pair(txid, CCoinsCacheEntry())).first;
+    tmp.swap(ret->second.coins);
+    if (ret->second.coins.IsPruned()) {
+        // The parent only has an empty entry for this txid; we can consider our
+        // version as fresh.
+        ret->second.flags = CCoinsCacheEntry::FRESH;
+    }
     return ret;
 }
 
-CCoinsMap::const_iterator CCoinsViewCache::FetchCoins(const uint256 &txid) const {
-    /* Avoid redundant implementation with the const-cast.  */
-    return const_cast<CCoinsViewCache*>(this)->FetchCoins(txid);
+bool CCoinsViewCache::GetCoins(const uint256 &txid, CCoins &coins) const {
+    CCoinsMap::const_iterator it = FetchCoins(txid);
+    if (it != cacheCoins.end()) {
+        coins = it->second.coins;
+        return true;
+    }
+    return false;
 }
 
-CCoins &CCoinsViewCache::GetCoins(const uint256 &txid) {
-    CCoinsMap::iterator it = FetchCoins(txid);
-    assert(it != cacheCoins.end());
-    return it->second;
+CCoinsModifier CCoinsViewCache::ModifyCoins(const uint256 &txid) {
+    assert(!hasModifier);
+    hasModifier = true;
+    std::pair<CCoinsMap::iterator, bool> ret = cacheCoins.insert(std::make_pair(txid, CCoinsCacheEntry()));
+    if (ret.second) {
+        if (!base->GetCoins(txid, ret.first->second.coins)) {
+            // The parent view does not have this entry; mark it as fresh.
+            ret.first->second.coins.Clear();
+            ret.first->second.flags = CCoinsCacheEntry::FRESH;
+        } else if (ret.first->second.coins.IsPruned()) {
+            // The parent view only has a pruned entry for this; mark it as fresh.
+            ret.first->second.flags = CCoinsCacheEntry::FRESH;
+        }
+    }
+    // Assume that whenever ModifyCoins is called, the entry will be modified.
+    ret.first->second.flags |= CCoinsCacheEntry::DIRTY;
+    return CCoinsModifier(*this, ret.first);
 }
 
 const CCoins* CCoinsViewCache::AccessCoins(const uint256 &txid) const {
@@ -115,22 +126,17 @@ const CCoins* CCoinsViewCache::AccessCoins(const uint256 &txid) const {
     if (it == cacheCoins.end()) {
         return NULL;
     } else {
-        return &it->second;
+        return &it->second.coins;
     }
 }
 
-bool CCoinsViewCache::SetCoins(const uint256 &txid, const CCoins &coins) {
-    cacheCoins[txid] = coins;
-    return true;
-}
-
 bool CCoinsViewCache::HaveCoins(const uint256 &txid) const {
     CCoinsMap::const_iterator it = FetchCoins(txid);
     // We're using vtx.empty() instead of IsPruned here for performance reasons,
     // as we only care about the case where an transaction was replaced entirely
     // in a reorganization (which wipes vout entirely, as opposed to spending
     // which just cleans individual outputs).
-    return (it != cacheCoins.end() && !it->second.vout.empty());
+    return (it != cacheCoins.end() && !it->second.coins.vout.empty());
 }
 
 uint256 CCoinsViewCache::GetBestBlock() const {
@@ -139,14 +145,39 @@ uint256 CCoinsViewCache::GetBestBlock() const {
     return hashBlock;
 }
 
-bool CCoinsViewCache::SetBestBlock(const uint256 &hashBlockIn) {
+void CCoinsViewCache::SetBestBlock(const uint256 &hashBlockIn) {
     hashBlock = hashBlockIn;
-    return true;
 }
 
 bool CCoinsViewCache::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlockIn) {
+    assert(!hasModifier);
     for (CCoinsMap::iterator it = mapCoins.begin(); it != mapCoins.end();) {
-        cacheCoins[it->first].swap(it->second);
+        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);
+                    CCoinsCacheEntry& entry = cacheCoins[it->first];
+                    entry.coins.swap(it->second.coins);
+                    entry.flags = CCoinsCacheEntry::DIRTY | CCoinsCacheEntry::FRESH;
+                }
+            } else {
+                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
+                    // it from the parent.
+                    cacheCoins.erase(itUs);
+                } else {
+                    // A normal modification.
+                    itUs->second.coins.swap(it->second.coins);
+                    itUs->second.flags |= CCoinsCacheEntry::DIRTY;
+                }
+            }
+        }
         CCoinsMap::iterator itOld = it++;
         mapCoins.erase(itOld);
     }
@@ -213,3 +244,15 @@ double CCoinsViewCache::GetPriority(const CTransaction &tx, int nHeight) const
     }
     return tx.ComputePriority(dResult);
 }
+
+CCoinsModifier::CCoinsModifier(CCoinsViewCache& cache_, CCoinsMap::iterator it_) : cache(cache_), it(it_) {}
+
+CCoinsModifier::~CCoinsModifier()
+{
+    assert(cache.hasModifier);
+    cache.hasModifier = false;
+    it->second.coins.Cleanup();
+    if ((it->second.flags & CCoinsCacheEntry::FRESH) && it->second.coins.IsPruned()) {
+        cache.cacheCoins.erase(it);
+    }
+}