Start/stop pattern for unchecked_map (#4577)

* Start/stop pattern for `unchecked_map`

* Remove flush function

nano/node/node.cpp

@@ -674,6 +674,7 @@ void nano::node::start ()
 	{
 		port_mapping.start ();
 	}
+	unchecked.start ();
 	wallets.start ();
 	rep_tiers.start ();
 	vote_processor.start ();

nano/node/unchecked_map.cpp

@@ -9,15 +9,37 @@
 nano::unchecked_map::unchecked_map (unsigned const max_unchecked_blocks, nano::stats & stats, bool const & disable_delete) :
 	max_unchecked_blocks{ max_unchecked_blocks },
 	stats{ stats },
-	disable_delete{ disable_delete },
-	thread{ [this] () { run (); } }
+	disable_delete{ disable_delete }
 {
 }
 
 nano::unchecked_map::~unchecked_map ()
 {
-	stop ();
-	thread.join ();
+	debug_assert (!thread.joinable ());
+}
+
+void nano::unchecked_map::start ()
+{
+	debug_assert (!thread.joinable ());
+
+	thread = std::thread ([this] () {
+		nano::thread_role::set (nano::thread_role::name::unchecked);
+		run ();
+	});
+}
+
+void nano::unchecked_map::stop ()
+{
+	{
+		nano::lock_guard<nano::mutex> lock{ mutex };
+		stopped = true;
+	}
+	condition.notify_all ();
+
+	if (thread.joinable ())
+	{
+		thread.join ();
+	}
 }
 
 void nano::unchecked_map::put (nano::hash_or_account const & dependency, nano::unchecked_info const & info)
@@ -30,6 +52,7 @@ void nano::unchecked_map::put (nano::hash_or_account const & dependency, nano::u
 	{
 		entries.get<tag_sequenced> ().pop_front ();
 	}
+
 	stats.inc (nano::stat::type::unchecked, nano::stat::detail::put);
 }
 
@@ -85,24 +108,6 @@ std::size_t nano::unchecked_map::count () const
 	return entries.size ();
 }
 
-void nano::unchecked_map::stop ()
-{
-	nano::unique_lock<nano::mutex> lock{ mutex };
-	if (!stopped)
-	{
-		stopped = true;
-		condition.notify_all (); // Notify flush (), run ()
-	}
-}
-
-void nano::unchecked_map::flush ()
-{
-	nano::unique_lock<nano::mutex> lock{ mutex };
-	condition.wait (lock, [this] () {
-		return stopped || (buffer.empty () && back_buffer.empty () && !writing_back_buffer);
-	});
-}
-
 void nano::unchecked_map::trigger (nano::hash_or_account const & dependency)
 {
 	nano::unique_lock<nano::mutex> lock{ mutex };
@@ -122,7 +127,6 @@ void nano::unchecked_map::process_queries (decltype (buffer) const & back_buffer
 
 void nano::unchecked_map::run ()
 {
-	nano::thread_role::set (nano::thread_role::name::unchecked);
 	nano::unique_lock<nano::mutex> lock{ mutex };
 	while (!stopped)
 	{
@@ -138,7 +142,6 @@ void nano::unchecked_map::run ()
 		}
 		else
 		{
-			condition.notify_all (); // Notify flush ()
 			condition.wait (lock, [this] () {
 				return stopped || !buffer.empty ();
 			});

nano/node/unchecked_map.hpp

@@ -25,6 +25,9 @@ class unchecked_map
 	unchecked_map (unsigned const max_unchecked_blocks, nano::stats &, bool const & do_delete);
 	~unchecked_map ();
 
+	void start ();
+	void stop ();
+
 	void put (nano::hash_or_account const & dependency, nano::unchecked_info const & info);
 	void for_each (
 	std::function<void (nano::unchecked_key const &, nano::unchecked_info const &)> action, std::function<bool ()> predicate = [] () { return true; });
@@ -35,8 +38,6 @@ class unchecked_map
 	void del (nano::unchecked_key const & key);
 	void clear ();
 	std::size_t count () const;
-	void stop ();
-	void flush ();
 
 	/**
 	 * Trigger requested dependencies
@@ -58,10 +59,12 @@ class unchecked_map
 	std::deque<nano::hash_or_account> buffer;
 	std::deque<nano::hash_or_account> back_buffer;
 	bool writing_back_buffer{ false };
+
 	bool stopped{ false };
 	nano::condition_variable condition;
 	nano::mutex mutex;
 	std::thread thread;
+
 	unsigned const max_unchecked_blocks;
 
 	void process_queries (decltype (buffer) const & back_buffer);