[erlang-bugs] Strange behaviors in supervisor module.

Zichen Cao <>
Thu Jun 16 19:45:38 CEST 2011


Hi,

I was testing supervisor module, and I found three strange behaviors in it.

start() ->
    Pid = spawn_link(fun child/0),
        {ok, Pid}.

child() ->
        receive
                exit -> exit(normal)
        end.

init(_) ->
        {ok, {{one_for_one, 30000, 10000},[]}}.

f_sup1()->
        {ok, Sup} = supervisor:start_link(?MODULE, []),
        {ok, Child} = supervisor:start_child(Sup, {child, {supervisor,start_link, [?MODULE,[]]},
                               temporary,infinity,supervisor,[?MODULE]}),
        exit(Child, kill),
        supervisor:delete_child(Sup, child).

f_sup2()->
        {ok, Sup} = supervisor:start_link(?MODULE, []),
        {ok, Child1} = supervisor:start_child(Sup, {child1, {?MODULE,start,[]}, temporary,1,worker, [?MODULE]}),
        {ok, Child2} = supervisor:start_child(Sup, {child2, {?MODULE,start,[]}, transient,1,worker, [?MODULE]}),
        Child1 ! exit,
        Child2 ! exit,
        timer:sleep(100),
        {supervisor:restart_child(Sup, child1),
         supervisor:restart_child(Sup, child2)}.

f_sup3()->
        {ok, Sup} = supervisor:start_link(?MODULE, []),
        {ok, Child} = supervisor:start_child(Sup, {child, {?MODULE,start,[]}, transient,10000,worker, [?MODULE]}),
        exit(Child, shutdown),
        timer:sleep(100),
        {Child, supervisor:which_children(Sup)}.

In f_sup1, after killing the child process, I try to delete it by calling supervisor:delete_child, it returns {error,running}.
In f_sup2, if a child processes exits with reason normal, a temporary child process cannot be restarted, but transient process can. So f_sup2 returns{{error,not_found},{ok,<0.364.0>}}. This seems inconsistent because a transient process that exits with reason normal is not supposed to be restarted.
In f_sup3, if a transient child process exits with the reason shutdown, it won't be restarted. It seems strange, since, a transient child process should be restarted unless it is terminated with the reason normal.

Zichen Cao


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