[erlang-questions] How to upgrade runningapplications repeatedly

[Ulf Wiger (TN/EAB)]

Matthias Lang wrote:
> 
> Roger Larsson writes:
>  > I think that this is your problem
>  >
>  > On Thursday 07 June 2007 22:06, Bo wrote:
>  > > start_server(L) ->
>  > >     process_flag(trap_exit, true),
>  > >     register(test,
>  > >          spawn(fun() ->
>  > >             process_flag(trap_exit, true),  
>  > >             Val= (catch ?MODULE:server_loop([L])),  
>  > > io:format("Server terminated with:~p~n",[Val])
>  > >            end)).
>  >
>  > This one function that will not upgrade itself. Requiring 
> the  > original version to remain in memory.
> 
> You're right, I missed that.
> 
>  > Simple test move this part to another module.
>  > (But I think the real solution would be to use spawn_link)
> 
> spawn_link on its own will make the problem more obvious, but 
> it won't make it go away.

Instead of writing

Val = (catch ?MODULE:server_loop([L])),

one can use proc_lib:spawn(fun() -> ... end)

With SASL running, this will give a crash report if the 
process terminates with Reason =/= normal.

Here's the relevant code from proc_lib.erl:

init_p(Parent,Ancestors,F) when function(F) ->
    put('$ancestors',[Parent|Ancestors]),
    put('$initial_call',F),
    Result = (catch F()),
    exit_p(Result,F).

exit_p({'EXIT',Reason},StartF) ->
    crash_report(Reason,StartF),
    exit(Reason);
exit_p(Reason,_) ->
    Reason.

BR,
Ulf W