From 60ef7268ba44209ca8601d9de9957cf73679714d Mon Sep 17 00:00:00 2001
From: Antioch Peverell <apeverell@protonmail.com>
Date: Sat, 6 Oct 2018 21:06:02 +0100
Subject: [PATCH] cleanup mine_block difficulty_iterator usage (#1674)

* take care with diff_iter (contains an active lmdb batch)

* rustfmt
---
 servers/src/grin/server.rs       | 4 +---
 servers/src/mining/mine_block.rs | 6 +++---
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/servers/src/grin/server.rs b/servers/src/grin/server.rs
index f67226e3..0935340e 100644
--- a/servers/src/grin/server.rs
+++ b/servers/src/grin/server.rs
@@ -395,10 +395,8 @@ impl Server {
 		// code clean. This may be handy for testing but not really needed
 		// for release
 		let diff_stats = {
-			let diff_iter = self.chain.difficulty_iter();
-
 			let last_blocks: Vec<Result<(u64, Difficulty), consensus::TargetError>> =
-				global::difficulty_data_to_vector(diff_iter)
+				global::difficulty_data_to_vector(self.chain.difficulty_iter())
 					.into_iter()
 					.skip(consensus::MEDIAN_TIME_WINDOW as usize)
 					.take(consensus::DIFFICULTY_ADJUST_WINDOW as usize)
diff --git a/servers/src/mining/mine_block.rs b/servers/src/mining/mine_block.rs
index d0ba3e69..f1862bdb 100644
--- a/servers/src/mining/mine_block.rs
+++ b/servers/src/mining/mine_block.rs
@@ -104,9 +104,9 @@ fn build_block(
 		now_sec = head_sec + 1;
 	}
 
-	// get the difficulty our block should be at
-	let diff_iter = chain.difficulty_iter();
-	let difficulty = consensus::next_difficulty(diff_iter).unwrap();
+	// Determine the difficulty our block should be at.
+	// Note: do not keep the difficulty_iter in scope (it has an active batch).
+	let difficulty = consensus::next_difficulty(chain.difficulty_iter()).unwrap();
 
 	// extract current transaction from the pool
 	// TODO - we have a lot of unwrap() going on in this fn...