Ignore tracking of requests when MaxConn = infinity

There is no need to contact the server and track requests unless being
asked to do so by the user. It's going to be faster and more efficient
to not track anything when being told tracking doesn't matter.

Whenever the max connections is set to infinity, the connections
counting key is not created, or is deleted if it existed already.
When using a numeric value, the connection count is created or
maintained if it existed already.

Moreover, trying to reduce a listener's counter while the max connection
number is set to `infinity` will return 0 and avoid all counting
operations as they are meaningless.

src/ranch_acceptor.erl

@@ -56,8 +56,13 @@ loop(LSocket, Transport, Protocol, MaxConns, Opts, ListenerPid, ConnsSup) ->
 				[ListenerPid, CSocket, Transport, Protocol, Opts]),
 			Transport:controlling_process(CSocket, ConnPid),
 			ConnPid ! {shoot, ListenerPid},
-			NbConns = ranch_listener:add_connection(ListenerPid, ConnPid),
-			{ok, MaxConns2} = maybe_wait(ListenerPid, MaxConns, NbConns),
+			{ok, MaxConns2} = case MaxConns of
+				infinity ->
+					{ok, infinity};
+				_ ->
+					NbConns = ranch_listener:add_connection(ListenerPid, ConnPid),
+					maybe_wait(ListenerPid, MaxConns, NbConns)
+			end,
 			?MODULE:init(LSocket, Transport, Protocol,
 				MaxConns2, Opts, ListenerPid, ConnsSup);
 		%% Upgrade the max number of connections allowed concurrently.

src/ranch_listener.erl

@@ -69,8 +69,14 @@ add_connection(ServerPid, ConnPid) ->
 %% connections.
 -spec remove_connection(pid()) -> non_neg_integer().
 remove_connection(ServerPid) ->
-	ok = gen_server:cast(ServerPid, remove_connection),
-	ranch_server:remove_connection(ServerPid).
+	try
+		Count = ranch_server:remove_connection(ServerPid),
+		ok = gen_server:cast(ServerPid, remove_connection),
+		Count
+	catch
+		error:badarg -> % Max conns = infinity
+			0
+	end.
 
 %% @doc Return the listener's port.
 -spec get_port(pid()) -> {ok, inet:port_number()}.
@@ -105,8 +111,12 @@ set_protocol_options(ServerPid, ProtoOpts) ->
 %% gen_server.
 
 %% @private
+init([Ref, infinity, ProtoOpts]) ->
+	ok = ranch_server:insert_listener(Ref, self()),
+	{ok, #state{ref=Ref, max_conns=infinity, proto_opts=ProtoOpts}};
 init([Ref, MaxConns, ProtoOpts]) ->
 	ok = ranch_server:insert_listener(Ref, self()),
+	ranch_server:add_connections_counter(self()),
 	{ok, #state{ref=Ref, max_conns=MaxConns, proto_opts=ProtoOpts}}.
 
 %% @private
@@ -115,9 +125,19 @@ handle_call(get_port, _From, State=#state{port=Port}) ->
 handle_call(get_max_connections, _From, State=#state{max_conns=MaxConns}) ->
 	{reply, {ok, MaxConns}, State};
 handle_call({set_max_connections, MaxConnections}, _From,
-		State=#state{ref=Ref}) ->
+		State=#state{ref=Ref, max_conns=CurrMax, rm_diff=CurrDiff}) ->
+	RmDiff = case {MaxConnections, CurrMax} of
+		{infinity, _} -> % moving to infinity, delete connection key
+			ranch_server:remove_connections_counter(self()),
+			0;
+		{_, infinity} -> % moving away from infinity, create connection key
+			ranch_server:add_connections_counter(self()),
+			CurrDiff;
+		{_, _} -> % stay current
+			CurrDiff
+	end,
 	ranch_server:send_to_acceptors(Ref, {set_max_conns, MaxConnections}),
-	{reply, ok, State#state{max_conns=MaxConnections}};
+	{reply, ok, State#state{max_conns=MaxConnections, rm_diff=RmDiff}};
 handle_call(get_protocol_options, _From, State=#state{proto_opts=ProtoOpts}) ->
 	{reply, {ok, ProtoOpts}, State};
 handle_call({set_protocol_options, ProtoOpts}, _From, State=#state{ref=Ref}) ->
@@ -132,6 +152,8 @@ handle_call(_, _From, State) ->
 handle_cast({add_connection, ConnPid}, State) ->
 	_ = erlang:monitor(process, ConnPid),
 	{noreply, State};
+handle_cast(remove_connection, State=#state{max_conns=infinity}) ->
+	{noreply, State};
 handle_cast(remove_connection, State=#state{rm_diff=RmDiff}) ->
 	{noreply, State#state{rm_diff=RmDiff + 1}};
 handle_cast({set_port, Port}, State) ->

src/ranch_server.erl

@@ -27,6 +27,8 @@
 -export([add_connection/1]).
 -export([count_connections/1]).
 -export([remove_connection/1]).
+-export([add_connections_counter/1]).
+-export([remove_connections_counter/1]).
 
 %% gen_server.
 -export([init/1]).
@@ -95,7 +97,12 @@ add_connection(ListenerPid) ->
 %% @doc Count the number of connections in the connection pool.
 -spec count_connections(pid()) -> non_neg_integer().
 count_connections(ListenerPid) ->
-	ets:update_counter(?TAB, {connections, ListenerPid}, 0).
+	try
+		ets:update_counter(?TAB, {connections, ListenerPid}, 0)
+	catch
+		error:badarg -> % Max conns = infinity
+			0
+	end.
 
 %% @doc Remove a connection from the connection pool.
 %%
@@ -104,6 +111,21 @@ count_connections(ListenerPid) ->
 remove_connection(ListenerPid) ->
 	ets:update_counter(?TAB, {connections, ListenerPid}, -1).
 
+
+%% @doc Add a connections counter to the connection pool
+%%
+%% Should only be used by ranch listeners when settings regarding the max
+%% number of connections change.
+add_connections_counter(Pid) ->
+	true = ets:insert_new(?TAB, {{connections, Pid}, 0}).
+
+%% @doc remove a connections counter from the connection pool
+%%
+%% Should only be used by ranch listeners when settings regarding the max
+%% number of connections change.
+remove_connections_counter(Pid) ->
+	true = ets:delete(?TAB, {connections, Pid}).
+
 %% gen_server.
 
 %% @private
@@ -117,7 +139,6 @@ handle_call(_Request, _From, State) ->
 %% @private
 handle_cast({insert_listener, Ref, Pid}, State=#state{monitors=Monitors}) ->
 	true = ets:insert_new(?TAB, {{acceptors, Ref}, []}),
-	true = ets:insert_new(?TAB, {{connections, Pid}, 0}),
 	MonitorRef = erlang:monitor(process, Pid),
 	{noreply, State#state{
 		monitors=[{{MonitorRef, Pid}, {listener, Ref}}|Monitors]}};
@@ -157,7 +178,7 @@ code_change(_OldVsn, State, _Extra) ->
 remove_process(Key = {listener, Ref}, MonitorRef, Pid, Monitors) ->
 	true = ets:delete(?TAB, Key),
 	true = ets:delete(?TAB, {acceptors, Ref}),
-	true = ets:delete(?TAB, {connections, Pid}),
+	remove_connections_counter(Pid),
 	lists:keydelete({MonitorRef, Pid}, 1, Monitors);
 remove_process(Key = {acceptors, _}, MonitorRef, Pid, Monitors) ->
 	try

test/acceptor_SUITE.erl

@@ -40,6 +40,7 @@
 -export([tcp_max_connections/1]).
 -export([tcp_max_connections_and_beyond/1]).
 -export([tcp_set_max_connections/1]).
+-export([tcp_infinity_max_connections/1]).
 -export([tcp_upgrade/1]).
 
 %% supervisor.
@@ -58,6 +59,7 @@ groups() ->
 		tcp_active_echo,
 		tcp_echo,
 		tcp_max_connections,
+		tcp_infinity_max_connections,
 		tcp_max_connections_and_beyond,
 		tcp_set_max_connections,
 		tcp_upgrade
@@ -275,6 +277,25 @@ tcp_set_max_connections(_) ->
 	10 = receive_loop(connected, 1000),
 	20 = ranch:get_max_connections(tcp_set_max_connections).
 
+tcp_infinity_max_connections(_) ->
+	{ok, _} = ranch:start_listener(tcp_infinity_max_connections, 1,
+		ranch_tcp, [{port, 0}, {max_connections, 10}],
+		notify_and_wait_protocol, [{msg, connected}, {pid, self()}]),
+	Port = ranch:get_port(tcp_infinity_max_connections),
+	%% @todo We'll probably want a more direct interface to count_connections.
+	ListenerPid = ranch_server:lookup_listener(tcp_infinity_max_connections),
+	ok = connect_loop(Port, 20, 0),
+	10 = ranch_server:count_connections(ListenerPid),
+	10 = receive_loop(connected, 1000),
+	10 = ranch:get_max_connections(tcp_infinity_max_connections),
+	ranch:set_max_connections(tcp_infinity_max_connections, infinity),
+	0 = ranch_server:count_connections(ListenerPid),
+	infinity = ranch:get_max_connections(tcp_infinity_max_connections),
+	ranch:set_max_connections(tcp_infinity_max_connections, 10),
+	0 = ranch_server:count_connections(ListenerPid),
+	10 = receive_loop(connected, 1000),
+	10 = ranch_server:count_connections(ListenerPid). % count could be off
+
 tcp_upgrade(_) ->
 	receive after 20000 -> ok end,
 	{ok, _} = ranch:start_listener(tcp_upgrade, 1,