From b0875eb3fea0934f3a6651fbc22aac12e33e15e5 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Sun, 24 Aug 2014 02:08:05 +0200
Subject: Allow BatchWrite to destroy its input, reducing copying

---
 src/coins.cpp | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

(limited to 'src/coins.cpp')

diff --git a/src/coins.cpp b/src/coins.cpp
index fe40911db7..6137b51c55 100644
--- a/src/coins.cpp
+++ b/src/coins.cpp
@@ -57,7 +57,7 @@ bool CCoinsView::SetCoins(const uint256 &txid, const CCoins &coins) { return fal
 bool CCoinsView::HaveCoins(const uint256 &txid) { return false; }
 uint256 CCoinsView::GetBestBlock() { return uint256(0); }
 bool CCoinsView::SetBestBlock(const uint256 &hashBlock) { return false; }
-bool CCoinsView::BatchWrite(const CCoinsMap &mapCoins, const uint256 &hashBlock) { return false; }
+bool CCoinsView::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) { return false; }
 bool CCoinsView::GetStats(CCoinsStats &stats) { return false; }
 
 
@@ -68,7 +68,7 @@ bool CCoinsViewBacked::HaveCoins(const uint256 &txid) { return base->HaveCoins(t
 uint256 CCoinsViewBacked::GetBestBlock() { return base->GetBestBlock(); }
 bool CCoinsViewBacked::SetBestBlock(const uint256 &hashBlock) { return base->SetBestBlock(hashBlock); }
 void CCoinsViewBacked::SetBackend(CCoinsView &viewIn) { base = &viewIn; }
-bool CCoinsViewBacked::BatchWrite(const CCoinsMap &mapCoins, const uint256 &hashBlock) { return base->BatchWrite(mapCoins, hashBlock); }
+bool CCoinsViewBacked::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) { return base->BatchWrite(mapCoins, hashBlock); }
 bool CCoinsViewBacked::GetStats(CCoinsStats &stats) { return base->GetStats(stats); }
 
 CCoinsKeyHasher::CCoinsKeyHasher() : salt(GetRandHash()) {}
@@ -130,17 +130,19 @@ bool CCoinsViewCache::SetBestBlock(const uint256 &hashBlockIn) {
     return true;
 }
 
-bool CCoinsViewCache::BatchWrite(const CCoinsMap &mapCoins, const uint256 &hashBlockIn) {
-    for (CCoinsMap::const_iterator it = mapCoins.begin(); it != mapCoins.end(); it++)
-        cacheCoins[it->first] = it->second;
+bool CCoinsViewCache::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlockIn) {
+    for (CCoinsMap::iterator it = mapCoins.begin(); it != mapCoins.end();) {
+        cacheCoins[it->first].swap(it->second);
+        CCoinsMap::iterator itOld = it++;
+        mapCoins.erase(itOld);
+    }
     hashBlock = hashBlockIn;
     return true;
 }
 
 bool CCoinsViewCache::Flush() {
     bool fOk = base->BatchWrite(cacheCoins, hashBlock);
-    if (fOk)
-        cacheCoins.clear();
+    cacheCoins.clear();
     return fOk;
 }
 
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