From c8b6debc43acf78f95d75e4622736191c614b5a8 Mon Sep 17 00:00:00 2001
From: Colin LeMahieu <clemahieu@gmail.com>
Date: Fri, 12 Apr 2024 20:09:50 +0100
Subject: [PATCH 1/2] Clean up write_queue::wait.

Add consistency check to ensure the writer token is not already queued since they're waited for by value.
Change wait-loop to use the predicated overload of wait.
---
 nano/store/write_queue.cpp | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/nano/store/write_queue.cpp b/nano/store/write_queue.cpp
index cdc7f41ff8..b50809a32c 100644
--- a/nano/store/write_queue.cpp
+++ b/nano/store/write_queue.cpp
@@ -73,18 +73,14 @@ nano::store::write_guard nano::store::write_queue::wait (writer writer)
 	}
 
 	nano::unique_lock<nano::mutex> lk (mutex);
+	debug_assert (std::none_of (queue.cbegin (), queue.cend (), [writer] (auto const & item) { return item == writer; }));
 	// Add writer to the end of the queue if it's not already waiting
 	auto exists = std::find (queue.cbegin (), queue.cend (), writer) != queue.cend ();
 	if (!exists)
 	{
 		queue.push_back (writer);
 	}
-
-	while (queue.front () != writer)
-	{
-		cv.wait (lk);
-	}
-
+	cv.wait (lk, [&] () { return queue.front () == writer; });
 	return write_guard (guard_finish_callback);
 }
 

From f220b450195324f2a9363c784e087b089c5b3deb Mon Sep 17 00:00:00 2001
From: Colin LeMahieu <clemahieu@gmail.com>
Date: Sat, 13 Apr 2024 11:40:52 +0100
Subject: [PATCH 2/2] Change vote_generator to use write_queue when acquiring
 db transaction.

Previously the vote_generator was not respecting the write_queue.
---
 nano/node/vote_generator.cpp | 1 +
 nano/store/write_queue.hpp   | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/nano/node/vote_generator.cpp b/nano/node/vote_generator.cpp
index addc721921..c5cac3b77b 100644
--- a/nano/node/vote_generator.cpp
+++ b/nano/node/vote_generator.cpp
@@ -94,6 +94,7 @@ void nano::vote_generator::process_batch (std::deque<queue_entry_t> & batch)
 {
 	std::deque<candidate_t> candidates_new;
 	{
+		auto guard = ledger.store.write_queue.wait (is_final ? nano::store::writer::voting_final : nano::store::writer::voting);
 		auto transaction = ledger.store.tx_begin_write ({ tables::final_votes });
 
 		for (auto & [root, hash] : batch)
diff --git a/nano/store/write_queue.hpp b/nano/store/write_queue.hpp
index 674a7742bc..e01a6bf360 100644
--- a/nano/store/write_queue.hpp
+++ b/nano/store/write_queue.hpp
@@ -14,6 +14,8 @@ enum class writer
 	confirmation_height,
 	process_batch,
 	pruning,
+	voting,
+	voting_final,
 	testing // Used in tests to emulate a write lock
 };