[erlang-questions] Why does this crash?

Dmitry Klionsky <>
Sun Sep 27 13:10:25 CEST 2015


shell:catch_exception/1 is another trick for shell.
You don't need to unlink the process as the shell isn't get killed if 
exceptions happen.

1> self().
<0.34.0>
2> 1/0.
** exception error: an error occurred when evaluating an arithmetic 
expression
      in operator  '/'/2
         called as 1 / 0
3> self().
<0.37.0>
4> catch_exception(true).
false
5> 1/0.
* exception error: an error occurred when evaluating an arithmetic 
expression
     in operator  '/'/2
        called as 1 / 0
6> self().
<0.37.0>
7>


On 09/27/2015 01:28 PM, Vimal Kumar wrote:
> Hi Jesper,
>
> I now implemented supervision trees along with the application 
> controller, and things now work as it should be.
>
> 1> application:start(mybank).
> ok
>
> 2> whereis(bank_server).
> <0.38.0>
>
> 3> bank_server:new_user(user1, "d3fault").
> {ok}
>
> 4> {_, UniqueId} = bank_server:login(user1, "d3fault").
> {ok,"OsNTJVIQgyb9ERHg3q9SLg=="}
>
> 5> bank_server:new_user(user2, "d3fault").
> {ok}
>
> 6> {_, UniqueId} = bank_server:login(user2, "d3fault").
> ** exception error: no match of right hand side value {ok, 
> "w7MJ1HQrHIDbVlNOh5bSpg=="}
>
> 7> whereis(bank_server).
> <0.38.0>
>
> Unlinking the process is a great tip for testing from shell, didn't 
> cross my mind.
>
> Thanks!
>
> On Sun, Sep 27, 2015 at 3:24 PM, Jesper Louis Andersen 
> < 
> <mailto:>> wrote:
>
>
>     On Sun, Sep 27, 2015 at 10:52 AM, Vimal Kumar <
>     <mailto:>> wrote:
>
>         Going to add supervisors into this system and learn more about it.
>
>
>     It doesn't happen in real systems, because the supervision trees
>     are linked to the application controller, and not the shell. If
>     you simply add a supervision tree, and link that tree to the
>     shell, you are usually not free of the problem.
>
>     When developing however, you can unlink the pid:
>
>     {ok, P} = foo:start_link().
>     unlink(P).
>
>     which will have P not die if the shell does.
>
>     The other resources to look out for are ETS tables, and port()'s,
>     that is network sockets and files. If their controlling process,
>     i.e. the shell, goes away, then that resource is
>     cleaned/reaped/closed again.
>
>
>     -- 
>     J.
>
>
>
>
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> 
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