[erlang-bugs] supervisor transient child error?

[Siri Hansen]

Hi Michael,

I think that the child spec is kept in the supervisor so that one is
allowed to do supervisor:restart_child/2. This has been the behavior at
least as far back as the git repository goes. And given that the text was
changed as far back as OTP-R8B,  I don't think that the old documentation
is a reason for changing this behavior.

Regards
/siri


2015-07-10 3:53 GMT+02:00 Michael Truog <mjtruog@REDACTED>:

> Hi,
>
> I have noticed that when the supervisor has a child process with the
> childspec restart set to transient, and the process terminates in a way
> that is not abnormal, the childspec remains within the supervisor.  This
> appears to be an error based on old documentation: "When a temporary
> child dies for any reason or a transient child dies normally, the child
> is removed from the supervisor." (
> http://www.erlang.org/documentation/doc-4.8.2/lib/stdlib-1.6.1/doc/html/supervisor.html).
> The new documentation states: "a transient child process will be
> restarted only if it terminates abnormally, i.e. with another exit reason
> than normal, shutdown or {shutdown,Term}" (
> http://www.erlang.org/doc/man/supervisor.html), and this statement is
> true with the current supervisor code.
>
> Is it an error that transient processes that terminate in a way that is
> not abnormal do not get removed from the supervisor?  I think it is, but I
> am not sure if this was accepted legacy behavior that the documentation
> didn't want to contradict.  I have an example below with output:
>
> -module(test).
> -behaviour(supervisor).
> -export([start_link/0, test_child/0, test/0, init/1]).
> start_link() ->
>     supervisor:start_link({local, ?MODULE}, ?MODULE, []).
> test_child() ->
>     {ok, erlang:spawn_link(fun() -> erlang:exit(normal) end)}.
> test() ->
>     ChildSpec = {test, {test, test_child, []}, transient, 2000, worker,
> []},
>     supervisor:start_child(?MODULE, ChildSpec).
> init([]) ->
>     {ok, {{one_for_one, 5, 300}, []}}.
>
>
> Erlang/OTP 18 [erts-7.0] [source] [64-bit] [smp:2:2] [ds:2:2:10]
> [async-threads:10] [kernel-poll:false]
>
> Eshell V7.0  (abort with ^G)
> 1> {ok, Sup} = test:start_link().
> {ok,<0.35.0>}
> 2> erlang:unlink(Sup).
> true
> 3> {ok, P} = test:test().
> {ok,<0.38.0>}
> 4> erlang:is_process_alive(P).
> false
> 5> supervisor:which_children(test).
> [{test,undefined,worker,[]}]
> 6> test:test().
> {error,already_present}
>
> Isn't keeping the entry in the supervisor, after a termination that is not
> abnormal, an error?
>
> Thanks,
> Michael
>
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>
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