Restrict hold on cs_main.

In BlockFactory::CreateNewBlock, hold on to cs_main only as short
as possible, namely while we access the active chain tip.  This helps
prevent potential deadlocks, and should in general make the code
run more fluently.

Author: domob1812

divi/src/BlockFactory.cpp

@@ -84,7 +84,6 @@ bool BlockFactory::AppendProofOfStakeToBlock(
 
 CBlockTemplate* BlockFactory::CreateNewBlock(const CScript& scriptPubKeyIn, bool fProofOfStake)
 {
-    LOCK(mainCS_);
     // Create new block
     std::unique_ptr<CBlockTemplate> pblocktemplate(new CBlockTemplate());
     if (!pblocktemplate.get())
@@ -96,7 +95,10 @@ CBlockTemplate* BlockFactory::CreateNewBlock(const CScript& scriptPubKeyIn, bool
         block.nVersion = settings.GetArg("-blockversion", block.nVersion);
     }
 
-    pblocktemplate->previousBlockIndex = chain_.Tip();
+    {
+        LOCK(mainCS_);
+        pblocktemplate->previousBlockIndex = chain_.Tip();
+    }
     if(!pblocktemplate->previousBlockIndex) return NULL;
 
     // Create coinbase tx