Avoid deadlock when have past future blocks.

libethereum/BlockQueue.cpp

@@ -136,27 +136,28 @@ bool BlockQueue::doneDrain(h256s const& _bad)
 
 void BlockQueue::tick(BlockChain const& _bc)
 {
-	UpgradableGuard l(m_lock);
-	if (m_future.empty())
-		return;
+	vector<bytes> todo;
+	{
+		UpgradableGuard l(m_lock);
+		if (m_future.empty())
+			return;
 
-	cblockq << "Checking past-future blocks...";
+		cblockq << "Checking past-future blocks...";
 
-	unsigned t = time(0);
-	if (t <= m_future.begin()->first)
-		return;
+		unsigned t = time(0);
+		if (t <= m_future.begin()->first)
+			return;
 
-	cblockq << "Past-future blocks ready.";
+		cblockq << "Past-future blocks ready.";
 
-	vector<bytes> todo;
-	{
-		UpgradeGuard l2(l);
-		auto end = m_future.lower_bound(t);
-		for (auto i = m_future.begin(); i != end; ++i)
-			todo.push_back(move(i->second));
-		m_future.erase(m_future.begin(), end);
+		{
+			UpgradeGuard l2(l);
+			auto end = m_future.lower_bound(t);
+			for (auto i = m_future.begin(); i != end; ++i)
+				todo.push_back(move(i->second));
+			m_future.erase(m_future.begin(), end);
+		}
 	}
-
 	cblockq << "Importing" << todo.size() << "past-future blocks.";
 
 	for (auto const& b: todo)