From 5cec1aad152115502f8ba0d7fcc1c3e40b915d7a Mon Sep 17 00:00:00 2001
From: obscuren <geffobscura@gmail.com>
Date: Fri, 15 May 2015 15:30:34 +0200
Subject: [PATCH] core, miner: fork resolving and restart miner after sync op

Fork resolving fixes #940
---
 core/chain_manager.go | 22 +++++++++++++++-------
 miner/miner.go        |  1 +
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/core/chain_manager.go b/core/chain_manager.go
index a0839ad41..2e8eb927d 100644
--- a/core/chain_manager.go
+++ b/core/chain_manager.go
@@ -577,10 +577,10 @@ func (self *ChainManager) InsertChain(chain types.Blocks) (int, error) {
 			// Compare the TD of the last known block in the canonical chain to make sure it's greater.
 			// At this point it's possible that a different chain (fork) becomes the new canonical chain.
 			if block.Td.Cmp(self.td) > 0 {
-				// Check for chain forks. If H(block.num - 1) != block.parent, we're on a fork and need to do some merging
-				if previous := self.getBlockByNumber(block.NumberU64() - 1); previous.Hash() != block.ParentHash() {
+				// chain fork
+				if block.ParentHash() != cblock.Hash() {
 					// during split we merge two different chains and create the new canonical chain
-					self.merge(previous, block)
+					self.merge(cblock, block)
 
 					queue[i] = ChainSplitEvent{block, logs}
 					queueEvent.splitCount++
@@ -641,9 +641,17 @@ func (self *ChainManager) diff(oldBlock, newBlock *types.Block) types.Blocks {
 		oldStart    = oldBlock
 		newStart    = newBlock
 	)
-	// first find common number
-	for newBlock = newBlock; newBlock.NumberU64() != oldBlock.NumberU64(); newBlock = self.GetBlock(newBlock.ParentHash()) {
-		newChain = append(newChain, newBlock)
+
+	// first reduce whoever is higher bound
+	if oldBlock.NumberU64() > newBlock.NumberU64() {
+		// reduce old chain
+		for oldBlock = oldBlock; oldBlock.NumberU64() != newBlock.NumberU64(); oldBlock = self.GetBlock(oldBlock.ParentHash()) {
+		}
+	} else {
+		// reduce new chain and append new chain blocks for inserting later on
+		for newBlock = newBlock; newBlock.NumberU64() != oldBlock.NumberU64(); newBlock = self.GetBlock(newBlock.ParentHash()) {
+			newChain = append(newChain, newBlock)
+		}
 	}
 
 	numSplit := newBlock.Number()
@@ -669,7 +677,7 @@ func (self *ChainManager) diff(oldBlock, newBlock *types.Block) types.Blocks {
 func (self *ChainManager) merge(oldBlock, newBlock *types.Block) {
 	newChain := self.diff(oldBlock, newBlock)
 
-	// insert blocks
+	// insert blocks. Order does not matter. Last block will be written in ImportChain itself which creates the new head properly
 	for _, block := range newChain {
 		self.insert(block)
 	}
diff --git a/miner/miner.go b/miner/miner.go
index 359be4032..6c220b1a6 100644
--- a/miner/miner.go
+++ b/miner/miner.go
@@ -47,6 +47,7 @@ func (self *Miner) update() {
 			atomic.StoreInt32(&self.canStart, 0)
 			if self.Mining() {
 				self.Stop()
+				atomic.StoreInt32(&self.shouldStart, 1)
 				glog.V(logger.Info).Infoln("Mining operation aborted due to sync operation")
 			}
 		case downloader.DoneEvent, downloader.FailedEvent: