GMT BZ29373: fix race condition just after connection establishment

The ubf listener has a window for a possible race condition just after
connection establishment.  TCP/IP data sent by the client can be
ignored before the contract driver process has been completely
initialized.  For normal ubf client and server interaction, this race
condition is not visiable due to the inherit network latency and to
client that is initially busy reading the server hello before sending
it's first request to the server.

ChangeLog

@@ -1,3 +1,7 @@
+2010-11-10 11:30 JST  norton
+        * src/contract_driver.erl, src/proc_socket_server.erl: Fix race
+        condition just after connection establishment.
+
 2010-10-23 17:00 JST  norton
         * src/ubf.erl: Various fixes for UBF(a) decoder.
 

src/contract_driver.erl

@@ -31,6 +31,7 @@ loop(Module, Contract, Pid, Socket) ->
     loop(Module, Contract, Pid, Socket, 16#ffffffff).
 
 loop(Module, Contract, Pid, Socket, Timeout) ->
+    inet:setopts(Socket, [{active, true}]),
     put('ubf_socket', Socket),
     Cont = Module:init(Contract),
     loop(Module, Contract, Pid, Socket, Timeout, Cont).

src/proc_socket_server.erl

@@ -59,8 +59,8 @@ start_raw_server(Name, Port, Max, SpawnOpts, Fun, PacketType, PacketSize) ->
         undefined ->
             Parent = self(),
             Pid = erlang:spawn_opt(?MODULE, cold_start,
-                                    [Parent, Name, Port, Max, Fun, PacketType, PacketSize],
-                                    [link | SpawnOpts]),
+                                   [Parent, Name, Port, Max, Fun, PacketType, PacketSize],
+                                   [link | SpawnOpts]),
             {ok, Pid};
         _Pid ->
             false
@@ -77,7 +77,7 @@ stop_server(Name) ->
         undefined ->
             ok;
         Pid ->
-	    ok = stop_server(Pid),
+            ok = stop_server(Pid),
             (catch unregister(Name)),
             ok
     end.
@@ -89,20 +89,20 @@ server_port(Name) ->
 server_port(Pid, Timeout) when is_pid(Pid) ->
     Pid ! {port, self()},
     receive
-	{Pid, Reply} ->
-	    Reply
+        {Pid, Reply} ->
+            Reply
     after Timeout ->
-	    timeout
+            timeout
     end;
 server_port(Port, Timeout) when is_integer(Port) ->
     Name = port_name(Port),
     server_port(Name, Timeout);
 server_port(Name, Timeout) ->
     case whereis(Name) of
-	undefined ->
-	    retrylater;
-	Pid ->
-	    server_port(Pid, Timeout)
+        undefined ->
+            retrylater;
+        Pid ->
+            server_port(Pid, Timeout)
     end.
 
 
@@ -112,20 +112,20 @@ server_status(Name) ->
 server_status(Pid, Timeout) when is_pid(Pid) ->
     Pid ! {status, self()},
     receive
-	{Pid, Reply} ->
-	    Reply
+        {Pid, Reply} ->
+            Reply
     after Timeout ->
-	    timeout
+            timeout
     end;
 server_status(Port, Timeout) when is_integer(Port) ->
     Name = port_name(Port),
     server_status(Name, Timeout);
 server_status(Name, Timeout) ->
     case whereis(Name) of
-	undefined ->
-	    retrylater;
-	Pid ->
-	    server_status(Pid, Timeout)
+        undefined ->
+            retrylater;
+        Pid ->
+            server_status(Pid, Timeout)
     end.
 
 
@@ -135,27 +135,27 @@ server_children(Name) ->
 server_children(Pid, Timeout) when is_pid(Pid) ->
     Pid ! {children, self()},
     receive
-	{Pid, Reply} ->
-	    Reply
+        {Pid, Reply} ->
+            Reply
     after Timeout ->
-	    timeout
+            timeout
     end;
 server_children(Port, Timeout) when is_integer(Port) ->
     Name = port_name(Port),
     server_children(Name, Timeout);
 server_children(Name, Timeout) ->
     case whereis(Name) of
-	undefined ->
-	    retrylater;
-	Pid ->
-	    server_children(Pid, Timeout)
+        undefined ->
+            retrylater;
+        Pid ->
+            server_children(Pid, Timeout)
     end.
 
 
 cold_start(Parent, Name, Port, Max, Fun, PacketType, PacketSize) ->
     process_flag(trap_exit, true),
     DefaultListenOptions =
-        [binary, {nodelay, true}, {active, true}, {reuseaddr, true}, {backlog, 4096}],
+        [binary, {nodelay, true}, {active, false}, {reuseaddr, true}, {backlog, 4096}],
     ListenOptions =
         case {PacketType, PacketSize} of
             {0,0} ->
@@ -168,13 +168,13 @@ cold_start(Parent, Name, Port, Max, Fun, PacketType, PacketSize) ->
                 DefaultListenOptions++[{packet,T}, {packet_size,S}]
         end,
     {ok, Listen} = gen_tcp:listen(Port, ListenOptions),
-    RegisterName = 
-	if Name =/= undefined ->
-		Name;
-	   true ->
-		{ok, RealPort} = inet:port(Listen),
-		port_name(RealPort)
-	end,
+    RegisterName =
+        if Name =/= undefined ->
+                Name;
+           true ->
+                {ok, RealPort} = inet:port(Listen),
+                port_name(RealPort)
+        end,
     register(RegisterName, self()),
     New = start_accept(Listen, Fun),
     socket_loop(Parent, Listen, New, [], 0, Max, Fun).
@@ -200,7 +200,7 @@ socket_loop(Parent, Listen, New, Active, Num, Max, Fun) ->
             Active1 = lists:delete(Pid, Active),
             possibly_start_another(Parent, New, Listen, Active1, length(Active1), Max, Fun);
         {port, From} ->
-	    {ok, Port} = inet:port(Listen),
+            {ok, Port} = inet:port(Listen),
             From ! {self(), Port},
             socket_loop(Parent, Listen, New, Active, Num, Max, Fun);
         {status, From} ->
@@ -210,8 +210,8 @@ socket_loop(Parent, Listen, New, Active, Num, Max, Fun) ->
             From ! {self(), Active},
             socket_loop(Parent, Listen, New, Active, Num, Max, Fun);
         Other ->
-	    io:format("*** YY Socket loop dropping:~p~n", [Other]),
-	    socket_loop(Parent, Listen, New, Active, Num, Max, Fun)
+            io:format("*** YY Socket loop dropping:~p~n", [Other]),
+            socket_loop(Parent, Listen, New, Active, Num, Max, Fun)
     end.
 
 
@@ -234,8 +234,8 @@ start_accept(Listen, Fun) ->
 start_child(Parent, Listen, Fun) ->
     case gen_tcp:accept(Listen) of
         {ok, Socket} ->
-            Parent ! {started, self()},             % tell the controller
-            inet:setopts(Socket, [{active, true}]), % before we activate socket
+            %% Kick off the parent
+            Parent ! {started, self()},
             %% Start the child
             case (catch Fun(Socket)) of
                 {'EXIT', normal} ->