From bbde1e99c893924dbef135f42c14f4df9828c6e5 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Sat, 11 Jan 2014 17:28:34 +0100
Subject: [PATCH] Limit the number of orphan blocks

In case the total number of orphan blocks in memory exceeds a limit
(currently set to 750), a random orphan block (which is not
depended on by another orphan block) is dropped. This means it will
need to be downloaded again, but it won't consume memory until then.
---
 src/main.cpp | 28 +++++++++++++++++++++++++++-
 src/main.h   |  2 ++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/main.cpp b/src/main.cpp
index 4532b776c6..d33ad2fa95 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1054,6 +1054,31 @@ uint256 static GetOrphanRoot(const uint256& hash)
     } while(true);
 }
 
+// Remove a random orphan block (which does not have any dependent orphans).
+void static PruneOrphanBlocks()
+{
+    if (mapOrphanBlocksByPrev.size() <= MAX_ORPHAN_BLOCKS)
+        return;
+
+    // Pick a random orphan block.
+    int pos = insecure_rand() % mapOrphanBlocksByPrev.size();
+    std::multimap<uint256, COrphanBlock*>::iterator it = mapOrphanBlocksByPrev.begin();
+    while (pos--) it++;
+
+    // As long as this block has other orphans depending on it, move to one of those successors.
+    do {
+        std::multimap<uint256, COrphanBlock*>::iterator it2 = mapOrphanBlocksByPrev.find(it->second->hashBlock);
+        if (it2 == mapOrphanBlocksByPrev.end())
+            break;
+        it = it2;
+    } while(1);
+
+    uint256 hash = it->second->hashBlock;
+    delete it->second;
+    mapOrphanBlocksByPrev.erase(it);
+    mapOrphanBlocks.erase(hash);
+}
+
 int64_t GetBlockValue(int nHeight, int64_t nFees)
 {
     int64_t nSubsidy = 50 * COIN;
@@ -2373,10 +2398,11 @@ bool ProcessBlock(CValidationState &state, CNode* pfrom, CBlock* pblock, CDiskBl
     // If we don't already have its previous block, shunt it off to holding area until we get it
     if (pblock->hashPrevBlock != 0 && !mapBlockIndex.count(pblock->hashPrevBlock))
     {
-        LogPrintf("ProcessBlock: ORPHAN BLOCK, prev=%s\n", pblock->hashPrevBlock.ToString());
+        LogPrintf("ProcessBlock: ORPHAN BLOCK %lu, prev=%s\n", (unsigned long)mapOrphanBlocks.size(), pblock->hashPrevBlock.ToString());
 
         // Accept orphans as long as there is a node to request its parents from
         if (pfrom) {
+            PruneOrphanBlocks();
             COrphanBlock* pblock2 = new COrphanBlock();
             {
                 CDataStream ss(SER_DISK, CLIENT_VERSION);
diff --git a/src/main.h b/src/main.h
index bbf6fce48b..05210e5164 100644
--- a/src/main.h
+++ b/src/main.h
@@ -45,6 +45,8 @@ static const unsigned int MAX_STANDARD_TX_SIZE = 100000;
 static const unsigned int MAX_BLOCK_SIGOPS = MAX_BLOCK_SIZE/50;
 /** The maximum number of orphan transactions kept in memory */
 static const unsigned int MAX_ORPHAN_TRANSACTIONS = MAX_BLOCK_SIZE/100;
+/** The maximum number of orphan blocks kept in memory */
+static const unsigned int MAX_ORPHAN_BLOCKS = 750;
 /** The maximum size of a blk?????.dat file (since 0.8) */
 static const unsigned int MAX_BLOCKFILE_SIZE = 0x8000000; // 128 MiB
 /** The pre-allocation chunk size for blk?????.dat files (since 0.8) */