Various performance tweaks to CCoinsView

* Pass txid's to CCoinsView functions by reference instead of by value
* Add a method to swap CCoins, and use it in some places to avoid a
  allocating copy + destruct.
* Optimize CCoinsViewCache::FetchCoins to do only a single search
  through the backing map.

4 files changed, 47 insertions, 37 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 84a5cdc17b..212240ec22 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -171,9 +171,9 @@ void static ResendWalletTransactions()
 // CCoinsView implementations
 //
 
-bool CCoinsView::GetCoins(uint256 txid, CCoins &coins) { return false; }
-bool CCoinsView::SetCoins(uint256 txid, const CCoins &coins) { return false; }
-bool CCoinsView::HaveCoins(uint256 txid) { return false; }
+bool CCoinsView::GetCoins(const uint256 &txid, CCoins &coins) { return false; }
+bool CCoinsView::SetCoins(const uint256 &txid, const CCoins &coins) { return false; }
+bool CCoinsView::HaveCoins(const uint256 &txid) { return false; }
 CBlockIndex *CCoinsView::GetBestBlock() { return NULL; }
 bool CCoinsView::SetBestBlock(CBlockIndex *pindex) { return false; }
 bool CCoinsView::BatchWrite(const std::map<uint256, CCoins> &mapCoins, CBlockIndex *pindex) { return false; }
@@ -181,9 +181,9 @@ bool CCoinsView::GetStats(CCoinsStats &stats) { return false; }
 
 
 CCoinsViewBacked::CCoinsViewBacked(CCoinsView &viewIn) : base(&viewIn) { }
-bool CCoinsViewBacked::GetCoins(uint256 txid, CCoins &coins) { return base->GetCoins(txid, coins); }
-bool CCoinsViewBacked::SetCoins(uint256 txid, const CCoins &coins) { return base->SetCoins(txid, coins); }
-bool CCoinsViewBacked::HaveCoins(uint256 txid) { return base->HaveCoins(txid); }
+bool CCoinsViewBacked::GetCoins(const uint256 &txid, CCoins &coins) { 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) { return base->HaveCoins(txid); }
 CBlockIndex *CCoinsViewBacked::GetBestBlock() { return base->GetBestBlock(); }
 bool CCoinsViewBacked::SetBestBlock(CBlockIndex *pindex) { return base->SetBestBlock(pindex); }
 void CCoinsViewBacked::SetBackend(CCoinsView &viewIn) { base = &viewIn; }
@@ -192,7 +192,7 @@ bool CCoinsViewBacked::GetStats(CCoinsStats &stats) { return base->GetStats(stat
 
 CCoinsViewCache::CCoinsViewCache(CCoinsView &baseIn, bool fDummy) : CCoinsViewBacked(baseIn), pindexTip(NULL) { }
 
-bool CCoinsViewCache::GetCoins(uint256 txid, CCoins &coins) {
+bool CCoinsViewCache::GetCoins(const uint256 &txid, CCoins &coins) {
     if (cacheCoins.count(txid)) {
         coins = cacheCoins[txid];
         return true;
@@ -204,29 +204,30 @@ bool CCoinsViewCache::GetCoins(uint256 txid, CCoins &coins) {
     return false;
 }
 
-std::map<uint256,CCoins>::iterator CCoinsViewCache::FetchCoins(uint256 txid) {
-    std::map<uint256,CCoins>::iterator it = cacheCoins.find(txid);
-    if (it != cacheCoins.end())
+std::map<uint256,CCoins>::iterator CCoinsViewCache::FetchCoins(const uint256 &txid) {
+    std::map<uint256,CCoins>::iterator it = cacheCoins.lower_bound(txid);
+    if (it != cacheCoins.end() && it->first == txid)
         return it;
     CCoins tmp;
     if (!base->GetCoins(txid,tmp))
-        return it;
-    std::pair<std::map<uint256,CCoins>::iterator,bool> ret = cacheCoins.insert(std::make_pair(txid, tmp));
-    return ret.first;
+        return cacheCoins.end();
+    std::map<uint256,CCoins>::iterator ret = cacheCoins.insert(it, std::make_pair(txid, CCoins()));
+    tmp.swap(ret->second);
+    return ret;
 }
 
-CCoins &CCoinsViewCache::GetCoins(uint256 txid) {
+CCoins &CCoinsViewCache::GetCoins(const uint256 &txid) {
     std::map<uint256,CCoins>::iterator it = FetchCoins(txid);
     assert(it != cacheCoins.end());
     return it->second;
 }
 
-bool CCoinsViewCache::SetCoins(uint256 txid, const CCoins &coins) {
+bool CCoinsViewCache::SetCoins(const uint256 &txid, const CCoins &coins) {
     cacheCoins[txid] = coins;
     return true;
 }
 
-bool CCoinsViewCache::HaveCoins(uint256 txid) {
+bool CCoinsViewCache::HaveCoins(const uint256 &txid) {
     return FetchCoins(txid) != cacheCoins.end();
 }
 
@@ -263,7 +264,7 @@ unsigned int CCoinsViewCache::GetCacheSize() {
     It does not check for spendings by memory pool transactions. */
 CCoinsViewMemPool::CCoinsViewMemPool(CCoinsView &baseIn, CTxMemPool &mempoolIn) : CCoinsViewBacked(baseIn), mempool(mempoolIn) { }
 
-bool CCoinsViewMemPool::GetCoins(uint256 txid, CCoins &coins) {
+bool CCoinsViewMemPool::GetCoins(const uint256 &txid, CCoins &coins) {
     if (base->GetCoins(txid, coins))
         return true;
     if (mempool.exists(txid)) {
@@ -274,7 +275,7 @@ bool CCoinsViewMemPool::GetCoins(uint256 txid, CCoins &coins) {
     return false;
 }
 
-bool CCoinsViewMemPool::HaveCoins(uint256 txid) {
+bool CCoinsViewMemPool::HaveCoins(const uint256 &txid) {
     return mempool.exists(txid) || base->HaveCoins(txid);
 }
 
diff --git a/src/main.h b/src/main.h
index edfea7b510..d5f7093e42 100644
--- a/src/main.h
+++ b/src/main.h
@@ -918,6 +918,15 @@ public:
     void Cleanup() {
         while (vout.size() > 0 && vout.back().IsNull())
             vout.pop_back();
+        if (vout.empty())
+            std::vector<CTxOut>().swap(vout);
+    }
+
+    void swap(CCoins &to) {
+        std::swap(to.fCoinBase, fCoinBase);
+        to.vout.swap(vout);
+        std::swap(to.nHeight, nHeight);
+        std::swap(to.nVersion, nVersion);
     }
 
     // equality test
@@ -2077,14 +2086,14 @@ class CCoinsView
 {
 public:
     // Retrieve the CCoins (unspent transaction outputs) for a given txid
-    virtual bool GetCoins(uint256 txid, CCoins &coins);
+    virtual bool GetCoins(const uint256 &txid, CCoins &coins);
 
     // Modify the CCoins for a given txid
-    virtual bool SetCoins(uint256 txid, const CCoins &coins);
+    virtual bool SetCoins(const uint256 &txid, const CCoins &coins);
 
     // Just check whether we have data for a given txid.
     // This may (but cannot always) return true for fully spent transactions
-    virtual bool HaveCoins(uint256 txid);
+    virtual bool HaveCoins(const uint256 &txid);
 
     // Retrieve the block index whose state this CCoinsView currently represents
     virtual CBlockIndex *GetBestBlock();
@@ -2110,9 +2119,9 @@ protected:
 
 public:
     CCoinsViewBacked(CCoinsView &viewIn);
-    bool GetCoins(uint256 txid, CCoins &coins);
-    bool SetCoins(uint256 txid, const CCoins &coins);
-    bool HaveCoins(uint256 txid);
+    bool GetCoins(const uint256 &txid, CCoins &coins);
+    bool SetCoins(const uint256 &txid, const CCoins &coins);
+    bool HaveCoins(const uint256 &txid);
     CBlockIndex *GetBestBlock();
     bool SetBestBlock(CBlockIndex *pindex);
     void SetBackend(CCoinsView &viewIn);
@@ -2131,9 +2140,9 @@ public:
     CCoinsViewCache(CCoinsView &baseIn, bool fDummy = false);
 
     // Standard CCoinsView methods
-    bool GetCoins(uint256 txid, CCoins &coins);
-    bool SetCoins(uint256 txid, const CCoins &coins);
-    bool HaveCoins(uint256 txid);
+    bool GetCoins(const uint256 &txid, CCoins &coins);
+    bool SetCoins(const uint256 &txid, const CCoins &coins);
+    bool HaveCoins(const uint256 &txid);
     CBlockIndex *GetBestBlock();
     bool SetBestBlock(CBlockIndex *pindex);
     bool BatchWrite(const std::map<uint256, CCoins> &mapCoins, CBlockIndex *pindex);
@@ -2141,7 +2150,7 @@ public:
     // Return a modifiable reference to a CCoins. Check HaveCoins first.
     // Many methods explicitly require a CCoinsViewCache because of this method, to reduce
     // copying.
-    CCoins &GetCoins(uint256 txid);
+    CCoins &GetCoins(const uint256 &txid);
 
     // Push the modifications applied to this cache to its base.
     // Failure to call this method before destruction will cause the changes to be forgotten.
@@ -2151,7 +2160,7 @@ public:
     unsigned int GetCacheSize();
 
 private:
-    std::map<uint256,CCoins>::iterator FetchCoins(uint256 txid);
+    std::map<uint256,CCoins>::iterator FetchCoins(const uint256 &txid);
 };
 
 /** CCoinsView that brings transactions from a memorypool into view.
@@ -2163,8 +2172,8 @@ protected:
 
 public:
     CCoinsViewMemPool(CCoinsView &baseIn, CTxMemPool &mempoolIn);
-    bool GetCoins(uint256 txid, CCoins &coins);
-    bool HaveCoins(uint256 txid);
+    bool GetCoins(const uint256 &txid, CCoins &coins);
+    bool HaveCoins(const uint256 &txid);
 };
 
 /** Global variable that points to the active CCoinsView (protected by cs_main) */
diff --git a/src/txdb.cpp b/src/txdb.cpp
index 78fa0279ba..ca4e6c9bd8 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -22,17 +22,17 @@ void static BatchWriteHashBestChain(CLevelDBBatch &batch, const uint256 &hash) {
 CCoinsViewDB::CCoinsViewDB(size_t nCacheSize, bool fMemory, bool fWipe) : db(GetDataDir() / "coins", nCacheSize, fMemory, fWipe) {
 }
 
-bool CCoinsViewDB::GetCoins(uint256 txid, CCoins &coins) { 
+bool CCoinsViewDB::GetCoins(const uint256 &txid, CCoins &coins) { 
     return db.Read(make_pair('c', txid), coins); 
 }
 
-bool CCoinsViewDB::SetCoins(uint256 txid, const CCoins &coins) {
+bool CCoinsViewDB::SetCoins(const uint256 &txid, const CCoins &coins) {
     CLevelDBBatch batch;
     BatchWriteCoins(batch, txid, coins);
     return db.WriteBatch(batch);
 }
 
-bool CCoinsViewDB::HaveCoins(uint256 txid) {
+bool CCoinsViewDB::HaveCoins(const uint256 &txid) {
     return db.Exists(make_pair('c', txid)); 
 }
 
diff --git a/src/txdb.h b/src/txdb.h
index ebac81b301..47496eddba 100644
--- a/src/txdb.h
+++ b/src/txdb.h
@@ -16,9 +16,9 @@ protected:
 public:
     CCoinsViewDB(size_t nCacheSize, bool fMemory = false, bool fWipe = false);
 
-    bool GetCoins(uint256 txid, CCoins &coins);
-    bool SetCoins(uint256 txid, const CCoins &coins);
-    bool HaveCoins(uint256 txid);
+    bool GetCoins(const uint256 &txid, CCoins &coins);
+    bool SetCoins(const uint256 &txid, const CCoins &coins);
+    bool HaveCoins(const uint256 &txid);
     CBlockIndex *GetBestBlock();
     bool SetBestBlock(CBlockIndex *pindex);
     bool BatchWrite(const std::map<uint256, CCoins> &mapCoins, CBlockIndex *pindex);