Adding destructor observer

nano/core_test/election.cpp

@@ -17,6 +17,22 @@ TEST (election, construction)
 	node, nano::dev::genesis, [] (auto const &) {}, [] (auto const &) {}, nano::election_behavior::normal);
 }
 
+// This tests the election destruction event notification
+// Since the notification is signalled in the destructor, it needs to be freed
+TEST (election, destructor_observer)
+{
+	std::atomic<bool> destroyed{ false };
+	{
+		nano::test::system system (1);
+		auto & node = *system.nodes[0];
+		auto election = std::make_shared<nano::election> (node, nano::dev::genesis, [] (auto const &) {}, [] (auto const &) {}, nano::election_behavior::normal);
+		election->destructor_observers.add ([&destroyed] (auto const & qualified_root) {
+			destroyed = true;
+		});
+	}
+	ASSERT_TRUE (destroyed);
+}
+
 TEST (election, behavior)
 {
 	nano::test::system system (1);

nano/node/election.cpp

@@ -32,6 +32,11 @@ nano::election::election (nano::node & node_a, std::shared_ptr<nano::block> cons
 	last_blocks.emplace (block_a->hash (), block_a);
 }
 
+nano::election::~election ()
+{
+	destructor_observers.notify (qualified_root);
+}
+
 void nano::election::confirm_once (nano::unique_lock<nano::mutex> & lock_a, nano::election_status_type type_a)
 {
 	debug_assert (lock_a.owns_lock ());

nano/node/election.hpp

@@ -138,7 +138,10 @@ class election final : public std::enable_shared_from_this<nano::election>
 
 public: // Interface
 	election (nano::node &, std::shared_ptr<nano::block> const & block, std::function<void (std::shared_ptr<nano::block> const &)> const & confirmation_action, std::function<void (nano::account const &)> const & vote_action, nano::election_behavior behavior);
+	~election ();
+	nano::observer_set<nano::qualified_root const &> destructor_observers;
 
+public:
 	std::shared_ptr<nano::block> find (nano::block_hash const &) const;
 	/*
 	 * Process vote. Internally uses cooldown to throttle non-final votes