From 940669657837e4a247a4d0746c12f52e8662f325 Mon Sep 17 00:00:00 2001
From: Gavin Andresen <gavinandresen@gmail.com>
Date: Tue, 6 Sep 2011 13:39:17 -0400
Subject: [PATCH] Fix AddAddress cs_mapaddresses/db transaction deadlock

---
 src/net.cpp |   36 +++++++++++++++++++++---------------
 1 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/src/net.cpp b/src/net.cpp
index 5fca17a..509d890 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -443,6 +443,10 @@ bool AddAddress(CAddress addr, int64 nTimePenalty, CAddrDB *pAddrDB)
     if (addr.ip == addrLocalHost.ip)
         return false;
     addr.nTime = max((int64)0, (int64)addr.nTime - nTimePenalty);
+    bool fUpdated = false;
+    bool fNew = false;
+    CAddress addrFound = addr;
+
     CRITICAL_BLOCK(cs_mapAddresses)
     {
         map<vector<unsigned char>, CAddress>::iterator it = mapAddresses.find(addr.GetKey());
@@ -451,16 +455,12 @@ bool AddAddress(CAddress addr, int64 nTimePenalty, CAddrDB *pAddrDB)
             // New address
             printf("AddAddress(%s)\n", addr.ToString().c_str());
             mapAddresses.insert(make_pair(addr.GetKey(), addr));
-            if (pAddrDB)
-                pAddrDB->WriteAddress(addr);
-            else
-                CAddrDB().WriteAddress(addr);
-            return true;
+            fUpdated = true;
+            fNew = true;
         }
         else
         {
-            bool fUpdated = false;
-            CAddress& addrFound = (*it).second;
+            addrFound = (*it).second;
             if ((addrFound.nServices | addr.nServices) != addrFound.nServices)
             {
                 // Services have been added
@@ -475,16 +475,22 @@ bool AddAddress(CAddress addr, int64 nTimePenalty, CAddrDB *pAddrDB)
                 addrFound.nTime = addr.nTime;
                 fUpdated = true;
             }
-            if (fUpdated)
-            {
-                if (pAddrDB)
-                    pAddrDB->WriteAddress(addrFound);
-                else
-                    CAddrDB().WriteAddress(addrFound);
-            }
         }
     }
-    return false;
+    // There is a nasty deadlock bug if this is done inside the cs_mapAddresses
+    // CRITICAL_BLOCK:
+    // Thread 1:  begin db transaction (locks inside-db-mutex)
+    //            then AddAddress (locks cs_mapAddresses)
+    // Thread 2:  AddAddress (locks cs_mapAddresses)
+    //             ... then db operation hangs waiting for inside-db-mutex
+    if (fUpdated)
+    {
+        if (pAddrDB)
+            pAddrDB->WriteAddress(addrFound);
+        else
+            CAddrDB().WriteAddress(addrFound);
+    }
+    return fNew;
 }
 
 void AddressCurrentlyConnected(const CAddress& addr)
-- 
1.7.1