Connector internals should always store connection implementation pointers rather than connection objects

[CuriousGeorgiy]

In our client tests we assume that a destructed connection is automatically closed:

tntcxx/test/ClientTest.cpp

Lines 238 to 262 in a3d0414

	template <class BUFFER, class NetProvider>
	void
	auto_close(Connector<BUFFER, NetProvider> &client)
	{
	TEST_INIT(0);
	{
	TEST_CASE("Without requests");
	Connection<Buf_t, NetProvider> conn(client);
	int rc = test_connect(client, conn, localhost, port);
	fail_unless(rc == 0);
	}
	{
	TEST_CASE("With requests");
	Connection<Buf_t, NetProvider> conn(client);
	int rc = test_connect(client, conn, localhost, port);
	fail_unless(rc == 0);
	rid_t f = conn.ping();
	fail_unless(!conn.futureIsReady(f));
	client.wait(conn, f, WAIT_TIMEOUT);
	fail_unless(conn.futureIsReady(f));
	std::optional<Response<Buf_t>> response = conn.getResponse(f);
	fail_unless(response != std::nullopt);
	}
	}

However, the connection destructor only unreferences the underlying connection implementation rather than closing it:

tntcxx/src/Client/Connection.hpp

Lines 397 to 401 in a3d0414

	template<class BUFFER, class NetProvider>
	Connection<BUFFER, NetProvider>::~Connection()
	{
	impl->unref();
	}

This is done to make connections copyable. If there were only user connection objects, the connection destructors would eventually trigger connection closure (when the connection implementation has no references left and it gets destroyed). But, currently, the LibevNetProvider uses connection objects internally:

tntcxx/src/Client/LibevNetProvider.hpp

Lines 53 to 64 in a3d0414

	template<class BUFFER, class Stream>
	struct WaitWatcher {
	WaitWatcher(Connector<BUFFER, LibevNetProvider<BUFFER, Stream>> *client,
	Connection<BUFFER, LibevNetProvider<BUFFER, Stream>> conn,
	struct ev_timer *t);
	struct ev_io in;
	struct ev_io out;
	Connector<BUFFER, LibevNetProvider<BUFFER, Stream>> *connector;
	Connection<BUFFER, LibevNetProvider<BUFFER, Stream>> connection;
	struct ev_timer *timer;
	};

Rather than using connection implementations like the EpollNetProvider:

tntcxx/src/Client/EpollNetProvider.hpp

Lines 119 to 124 in a3d0414

	template<class BUFFER, class Stream>
	void
	EpollNetProvider<BUFFER, Stream>::setPollSetting(Conn_t &conn, int setting) {
	struct epoll_event event;
	event.events = setting;
	event.data.ptr = conn.getImpl();

For the LibevNetProvider this means that connections will never get closed automatically, since there will always be an internal connection object.

However, it seems reasonable to rely on the fact that the lifetime of all connections used in the connector internals is tied to the user's connection objects. Hence, we should always store connection implementations rather than connection objects to avoid superfluous referencing.

[CuriousGeorgiy]

See also #123.