[erlang-questions] Unidirectional linking?

[Igor Ribeiro Sucupira]

Supposing someone used the same logic (with timeout/kill) to spawn the
parent process, the parent could be killed at any moment (but yeah: it
would be bad luck to have that happening right after it called
unlink).

Thanks.
Igor.

On Wed, May 25, 2011 at 3:20 AM, Mazen Harake <mazen.harake@REDACTED> wrote:
> Why would someone "kill the parent"? Do you have processes which are
> randomly choosing other processes to terminate? ;)
>
> If your answer is "No" then I would suggest that you just kill the worker
> processes that is taking to long, kill it in cold blood, imo.
>
> There is no reason to think about too many "if"-scenarios when the scenarios
> are too far fetched. Try the simple version first :)
>
> otherwise you can either trap_exits or use monitors instead.
>
> /M
>
> On 25 May 2011 08:00, Igor Ribeiro Sucupira <igorrs@REDACTED> 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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>
>