[erlang-questions] gen_server doesn't respond

[Attila Rajmund Nohl]

2013/6/4 Park, Sungjin <jinni.park@REDACTED>:
> 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.

Check process_info(Pid, backtrace) to see that which gen_server:call
(in your gen_server) is blocked. Then check that gen_server, maybe
that calls back to your gen_server or something like that.