[erlang-questions] gen_server doesn't respond

Park, Sungjin <>
Tue Jun 4 03:54:59 CEST 2013


Shell input/output logs below.

============================
4> process_info(pid(0,453,4757)).
[{current_function,{*gen,do_call,4*}},
 {initial_call,{proc_lib,init_p,5}},
 {status,*waiting*},
 {message_queue_len,1},
 {messages,[*{'$gen_call',{<0.26172.4841>,*
*                          #Ref<0.0.2946.93178>},*
*                         state}*]},
 {links,[<0.25337.4839>]},
 {dictionary,[{'$ancestors',[<0.452.4757>,<0.424.0>,
                             <0.423.0>,ranch_sup,<0.420.0>]},
              {'$initial_call',{my_session,init,1}}]},
 {trap_exit,true},
 {error_handler,error_handler},
 {priority,normal},
 {group_leader,<0.419.0>},
 {total_heap_size,1364},
 {heap_size,987},
 {stack_size,32},
 {reductions,1487},
 {garbage_collection,[{min_bin_vheap_size,46368},
                      {min_heap_size,233},
                      {fullsweep_after,65535},
                      {minor_gcs,8}]},
 {suspending,[]}]
=============================

As you can see the process has a message {..., state} in it's message queue
but still in waiting state. It doesn't respond to gen_server:call(Pid,
state) from this point on.  The process_info shows that the process is now
in gen:do_call/4 which is not under my control. The module has all the
fallback handlers for handle_call/3, handle_cast/2, handle_info/2 etc, so
that every message be matched. There are a couple of places in my project
where gen_server:call/2 used against this process.  I suppose that the
calls should timeout in 5 sec by default as is stated in the gen_server
specification.  So there should be no such case that the process stuck
indefinitely.



On Mon, Jun 3, 2013 at 7:39 PM, Aaron France <>wrote:

> Does it make any synchronous calls to other gen_servers?
>
>
> On Mon, Jun 3, 2013 at 12:34 PM, Tim Watson <>wrote:
>
>> Does the callback module execute any selective receives inside handlers
>> perhaps? If not, are you sure the message has actually arrived in that
>> process' mailbox, can you see unhandled messages in the message queue
>> (I.e., length > 0 whilst waiting)?
>>
>> On 3 Jun 2013, at 10:34, "Park, Sungjin" <> wrote:
>>
>> > Guys,
>> >
>> > I'm encountering cases when gen_server doesn't respond.
>> > In such cases, erlang:process_info/1 shows the process state 'waiting'
>> with some messages in the message_queue.  The messages have not been
>> consumed for tens of minutes at least.  Anybody has any idean about this?
>> >
>> >
>> > --
>> > Park, Sungjin
>> >
>> -------------------------------------------------------------------------------------------------------------------
>> > Peculiar travel suggestions are dancing lessons from god.
>> >   -- The Books of Bokonon
>> >
>> -------------------------------------------------------------------------------------------------------------------
>> > _______________________________________________
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>> > 
>> > http://erlang.org/mailman/listinfo/erlang-questions
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>> 
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>
>


-- 
Park, Sungjin
-------------------------------------------------------------------------------------------------------------------
Peculiar travel suggestions are dancing lessons from god.
  -- The Books of Bokonon
-------------------------------------------------------------------------------------------------------------------
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