From ab1f56072a796b0ff039d6690c6ac929dbcbf243 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Wed, 7 Oct 2015 23:34:55 +0200
Subject: [PATCH] Support -checkmempool=N, which runs checks on average once
 every N transactions

---
 src/init.cpp      | 5 ++++-
 src/txmempool.cpp | 9 ++++++---
 src/txmempool.h   | 4 ++--
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/src/init.cpp b/src/init.cpp
index 75c76e325..d899a1cf9 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -836,7 +836,10 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
         InitWarning(_("Warning: Unsupported argument -benchmark ignored, use -debug=bench."));
 
     // Checkmempool and checkblockindex default to true in regtest mode
-    mempool.setSanityCheck(GetBoolArg("-checkmempool", chainparams.DefaultConsistencyChecks()));
+    int ratio = std::min<int>(std::max<int>(GetArg("-checkmempool", chainparams.DefaultConsistencyChecks() ? 1 : 0), 0), 1000000);
+    if (ratio != 0) {
+        mempool.setSanityCheck(1.0 / ratio);
+    }
     fCheckBlockIndex = GetBoolArg("-checkblockindex", chainparams.DefaultConsistencyChecks());
     fCheckpointsEnabled = GetBoolArg("-checkpoints", true);
 
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index 1370cab0c..c379a45b4 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -311,7 +311,7 @@ CTxMemPool::CTxMemPool(const CFeeRate& _minRelayFee) :
     // Sanity checks off by default for performance, because otherwise
     // accepting transactions becomes O(N^2) where N is the number
     // of transactions in the pool
-    fSanityCheck = false;
+    nCheckFrequency = 0;
 
     minerPolicyEstimator = new CBlockPolicyEstimator(_minRelayFee);
 }
@@ -483,7 +483,7 @@ void CTxMemPool::removeCoinbaseSpends(const CCoinsViewCache *pcoins, unsigned in
             if (it2 != mapTx.end())
                 continue;
             const CCoins *coins = pcoins->AccessCoins(txin.prevout.hash);
-            if (fSanityCheck) assert(coins);
+            if (nCheckFrequency != 0) assert(coins);
             if (!coins || (coins->IsCoinBase() && ((signed long)nMemPoolHeight) - coins->nHeight < COINBASE_MATURITY)) {
                 transactionsToRemove.push_back(tx);
                 break;
@@ -553,7 +553,10 @@ void CTxMemPool::clear()
 
 void CTxMemPool::check(const CCoinsViewCache *pcoins) const
 {
-    if (!fSanityCheck)
+    if (nCheckFrequency == 0)
+        return;
+
+    if (insecure_rand() >= nCheckFrequency)
         return;
 
     LogPrint("mempool", "Checking mempool with %u transactions and %u inputs\n", (unsigned int)mapTx.size(), (unsigned int)mapNextTx.size());
diff --git a/src/txmempool.h b/src/txmempool.h
index c0eef0dd2..7d83decb5 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -277,7 +277,7 @@ public:
 class CTxMemPool
 {
 private:
-    bool fSanityCheck; //! Normally false, true if -checkmempool or -regtest
+    uint32_t nCheckFrequency; //! Value n means that n times in 2^32 we check.
     unsigned int nTransactionsUpdated;
     CBlockPolicyEstimator* minerPolicyEstimator;
 
@@ -338,7 +338,7 @@ public:
      * check does nothing.
      */
     void check(const CCoinsViewCache *pcoins) const;
-    void setSanityCheck(bool _fSanityCheck) { fSanityCheck = _fSanityCheck; }
+    void setSanityCheck(double dFrequency = 1.0) { nCheckFrequency = dFrequency * 4294967296.0; }
 
     // addUnchecked must updated state for all ancestors of a given transaction,
     // to track size/count of descendant transactions.  First version of