From d7412e4f331e2c9884839064d4f0a587b286f9c9 Mon Sep 17 00:00:00 2001
From: Hong Minhee <hong.minhee@gmail.com>
Date: Sat, 27 Apr 2019 00:00:34 +0900
Subject: [PATCH] Optimize rerender loop by avoiding random access

---
 Libplanet/Blockchain/BlockChain.cs | 28 +++++++++++++++++++++-------
 Libplanet/Tx/Transaction.cs        |  1 -
 2 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/Libplanet/Blockchain/BlockChain.cs b/Libplanet/Blockchain/BlockChain.cs
index 08dce11a563..3615f26082c 100644
--- a/Libplanet/Blockchain/BlockChain.cs
+++ b/Libplanet/Blockchain/BlockChain.cs
@@ -515,19 +515,30 @@ internal void Swap(BlockChain<T> other)
         {
             // Finds the branch point.
             Block<T> topmostCommon = null;
-            for (long i = Math.Min(other.Tip.Index, Tip.Index); i >= 0; i--)
+            long shorterHeight =
+                Math.Min(this.LongCount(), other.LongCount()) - 1;
+            for (
+                Block<T> t = this[shorterHeight], o = other[shorterHeight];
+                t.PreviousHash is HashDigest<SHA256> tp &&
+                    o.PreviousHash is HashDigest<SHA256> op;
+                t = Blocks[tp], o = other.Blocks[op]
+            )
             {
-                if (other[i].Equals(this[i]))
+                if (t.Equals(o))
                 {
-                    topmostCommon = this[i];
+                    topmostCommon = t;
                     break;
                 }
             }
 
             // Unrender stale actions.
-            for (long i = Tip.Index; i > (topmostCommon?.Index ?? -1); i--)
+            for (
+                Block<T> b = Tip;
+                !(b is null) && b.Index > (topmostCommon?.Index ?? -1) &&
+                    b.PreviousHash is HashDigest<SHA256> ph;
+                b = Blocks[ph]
+            )
             {
-                Block<T> b = this[i];
                 var actions = b.EvaluateActionsPerTx(a =>
                     GetStates(new[] { a }, b.PreviousHash).GetValueOrDefault(a)
                 ).Reverse();
@@ -554,9 +565,12 @@ internal void Swap(BlockChain<T> other)
             }
 
             // Render actions that had been behind.
-            for (long i = topmostCommon.Index + 1; i <= Tip.Index; i++)
+            IEnumerable<Block<T>> blocksToRender =
+                topmostCommon is Block<T> branchPoint
+                    ? this.SkipWhile(b => b.Index <= branchPoint.Index)
+                    : this;
+            foreach (Block<T> b in blocksToRender)
             {
-                Block<T> b = this[i];
                 var actions = b.EvaluateActionsPerTx(a =>
                     GetStates(new[] { a }, b.PreviousHash).GetValueOrDefault(a)
                 );
diff --git a/Libplanet/Tx/Transaction.cs b/Libplanet/Tx/Transaction.cs
index 8064de1f7f6..bf3ccc986b4 100644
--- a/Libplanet/Tx/Transaction.cs
+++ b/Libplanet/Tx/Transaction.cs
@@ -5,7 +5,6 @@
 using System.Globalization;
 using System.IO;
 using System.Linq;
-using System.Reflection;
 using System.Runtime.Serialization;
 using System.Security.Cryptography;
 using Libplanet.Action;