[erlang-questions] Unidirectional linking?

Bengt Kleberg <>
Wed May 25 08:16:28 CEST 2011


Greetings,

Uni-directional links are created with erlang:monitor/2. 

Does this help?


bengt

On Wed, 2011-05-25 at 08:00 +0200, Igor Ribeiro Sucupira wrote:
> Suppose there is a heavy operation Op that in some cases takes so long
> to finish that the caller loses interest in the result and gives up.
> 
> I want to perform that operation in a way that allows me to:
> 1) Interrupt its execution if it does not finish in N milliseconds.
> 2) Interrupt its execution if the calling process exits (here I'm
> already supposing Op has to be run in another Erlang process, due to
> goal 1).
> 
> To implement that, it seems unidirectional linking would be needed. Is
> there another safe and convenient way to do it?
> 
> The first idea I had was something like this:
> 
> Parent = self(),
> Child = spawn_link(fun() -> Parent ! (catch Op) end),
> receive Result -> Result
> after N -> unlink(Child), exit(Child, timeout), timeout
> end.
> 
> But, if Parent is killed by another process right after calling
> unlink, Child would be left executing.
> Another problem is that I don't want Parent to die if Child exits for
> non-timeout reasons (although it seems very unlikely in the code
> above, with the catch).
> 
> I was now thinking of substituting unlink(Child) with
> process_flag(trap_exit, true) and then kill Child, receive its exit
> message, set trap_exit to false again (I'm assuming it was false), and
> finally check if there were other exit messages (suiciding if it was
> the case).
> 
> But then the code would become too ugly, so I got lazy and decided to
> post to this list.  :-)
> 
> What do you think?
> 
> Thanks.
> Igor.
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