[erlang-questions] Why does adding an io:format call make my accept socket remain valid?

Robert Virding <>
Sun Mar 27 23:43:58 CEST 2016


To be even more specific all the 6 gen_server callbacks[*] must always be
run within the gen_server process, this irrespective of whether you are
testing or not.

Robert

[*] init/1, terminate/2, handle_call/3, handle-cast/2, handle_info/2,
code_change/3.

On 27 March 2016 at 15:13, Matthew Shapiro <> wrote:

> Well duh, now I feel like an idiot.
>
> Thanks,
>
> On Sun, Mar 27, 2016 at 5:31 AM, Vimal Kumar <> wrote:
>
>> Matthew,
>>
>> Like Nathaniel said, the eunit test should involve gen_server. Do not
>> test handle_cast/2 directly. Instead, run your test on an exported function
>> (say: Module:accept/0) which in turn should execute:
>>
>> gen_server:cast(?MODULE, accept)
>>
>> You can start a gen_server process, execute such tests and shut it down
>> properly using 'setup' Fixture:
>> http://learnyousomeerlang.com/eunit#fixtures
>>
>> Regards,
>> Vimal
>>
>> On Sun, Mar 27, 2016 at 10:15 AM, Nathaniel Waisbrot <
>> > wrote:
>>
>>> I don't know about your garbage-collection question, but:
>>>
>>> > Why does that io:format/3 call (only when after the spawn/3 call) keep
>>> the socket open and active for the spawned process?  I wouldn't expect it
>>> to be garbage collected because the spawned process holds a reference to it
>>> (and even adding it to the State in the return doesn't fix it).  Only other
>>> thing I could think of was that handle_cast is run in it's own process
>>> which closes the socket when it dies (since it has ownership), but that
>>> doesn't make sense from what I've read about OTP.
>>>
>>>
>>> Normally handle_cast would be run in the gen_server's process (since
>>> that's the whole point), but it looks to me like in your test:
>>>
>>>
>>> >   spawn_link(fun () -> tcp_listener_server:handle_cast(accept, State)
>>> end),
>>>
>>>
>>> you are bypassing gen_server and instead ... telling handle_cast to run
>>> in its own one-off process.
>>>
>>>
>>> Do you mean to be doing this? In your test code, you could call
>>> gen_server:start/1 and then gen_server:cast/2 and get the actual gen_server
>>> behavior.
>>>
>>> _______________________________________________
>>> erlang-questions mailing list
>>> 
>>> http://erlang.org/mailman/listinfo/erlang-questions
>>>
>>>
>>
>
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