[erlang-questions] Unidirectional linking?

Igor Ribeiro Sucupira <>
Wed May 25 08:24:23 CEST 2011


I couldn't see a way of using monitors in this example. I would need
the child process to monitor its parent, but the child is busy
performing Op.

Thanks.
Igor.

On Wed, May 25, 2011 at 3:16 AM, Bengt Kleberg
<> wrote:
> 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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