Luke Gorrie <>
Thu Feb 27 14:42:47 CET 2003

"Vlad Dumitrescu (EAW)" <> writes:

> Hi,
> I wonder about a thing. The following fun is an often used way to ensure that one uses "the one and only" server called ?MODULE.
> ensure_started() ->
>     case whereis(?MODULE) of
> 	undefined ->
> 	    Pid = proc_lib:spawn(?MODULE, init, []),
> 	    register(?MODULE, Pid),
> 	    {ok, Pid};
> 	Pid ->
> 	    {ok, Pid}
>     end.

This looks like code from fdoc. Sadly, I knew this was incorrect when
I wrote it, as is my ref()-less and monitor()-less 'call'
implementation when you get right down to it. Oops :-(

The trouble with registering in the server's init() function is that
then you need to synchronize the guy calling ensure_started() somehow,
since he needs to get the pid of the process that "wins the race." So
for "ensure_started" functions, I do like your second alternative with
the catch-and-retry.


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