[erlang-patches] wxe_server bug? (and patch)

Dan Gudmundsson <>
Wed Oct 14 15:52:16 CEST 2009


I'll fix the problem, in the right way(tm).

/Dan
PS: I just applied your wx_object patch but I allowed pids as well as
registered names and
added wx_object:cast/2.

On Wed, Oct 14, 2009 at 3:25 PM, Mazen Harake
<> wrote:
> A quick note:
> I just realized that this example doesn't work unless you have applied my
> previous patch for wx_object.erl. Either apply that or change the code to
> call the wx_object with the form (somehow) :)
>
> /Mazen
>
> Mazen Harake wrote:
>>
>> Hi,
>>
>> There is a situation in the wx library that causes the wxe_server to crash
>> when it receives a message with a pid which is considered by distributed
>> Erlang to come from another node when in fact it isn't. This happens when
>> net_kernel is started explicitly (I.e. Erlang going into distribution mode)
>> and an wx_object (which was created before net_kernel was started) is
>> destroyed.
>>
>> Here is a simple example:
>> Create this module:
>> -module(test).
>> -compile(export_all).
>>
>> start() ->
>>  wx:new(),
>>  wx_object:start_link({local, ?MODULE}, ?MODULE, wx:get_env(), []).
>>
>> close(_, _) ->
>>  wx_object:call(?MODULE, stop).
>>
>> init(Wx) ->
>>  wx:set_env(Wx),
>>  Mf = wxFrame:new(wx:null(),1,"",[{size,{300,300}}]),
>>  wxFrame:show(Mf),
>>  wxFrame:connect(Mf, close_window, [{callback, fun ?MODULE:close/2}]),
>>  {Mf, Mf}.
>>
>> handle_call(stop, _From, Mf) ->
>>  wxFrame:destroy(Mf),
>>  {stop, normal, ok, Mf}.
>>
>> terminate(normal, _) ->
>>  ok.
>>
>> Then run this in the shell:
>> Erlang R13B (erts-5.7.1) [smp:2:2] [rq:2] [async-threads:0]
>>
>> Eshell V5.7.1  (abort with ^G)
>> 1> c(test).
>> {ok,test}
>> 2> test:start().
>> {wx_ref,35,wxFrame,<0.42.0>}
>> 3>
>>
>> This should give you a small frame, don't close it yet,
>> Now do this:
>> 3> net_kernel:start([bad,shortnames]).
>> {ok,<0.49.0>}
>> ()4>
>>
>> Now close the frame and you should see:
>> =ERROR REPORT==== 14-Oct-2009::13:17:08 ===
>> ** Generic server <0.39.0> terminating
>> ** Last message in was {'_wxe_destroy_',<3.42.0>}
>> ** When Server state == {state,#Port<0.2605>,#Port<0.2602>,
>>
>>  {1,{<0.32.0>,{user,[],[],undefined},nil,nil}},
>>                              [<0.57.0>],
>>                              {1,{#Fun<test.close.2>,1,nil,nil}},
>>                              2}
>> ** Reason for termination ==
>> ** {badarg,[{erlang,is_process_alive,[<3.42.0>]},
>>           {wxe_server,handle_info,2},
>>           {gen_server,handle_msg,5},
>>           {proc_lib,init_p_do_apply,3}]}
>>
>>
>> The pid which comes from the port is not recognized as a local pid and
>> thus erlang:is_process_alive/1 will exit with badarg. My question is: Is
>> this a "feature" or a bug? I think this is a bug but I'm not sure what is
>> expected from the wx library point of view. IMHO it shouldn't crash and just
>> ignore it in this case because the wxe_server shouldn't be allowed to crash.
>>
>> Anyway I put in a patch as well just in case this is something that should
>> be fixed. The patch can be applied to both wx 0.98.1 and 0.98.3.
>>
>> Cheers,
>>
>> /Mazen
>>
>>
>>
>>
>> ------------------------------------------------------------------------
>>
>>
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>> erlang-patches (at) erlang.org
>
>
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>


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