Re: Aborting without killing

Yes, thanks Alan, that is roughly what I'm going to do.

Best,
Torbjörn

On Thu, Nov 14, 2013 at 4:59 PM, Alan Baljeu <[email protected]> wrote:
> It appears the answer is to signal throw(Something), and design the thread
> to catch that exception and hang around until you've retrieved the data,
> maybe with a mutex to suspend execution until you release it to die on its
> own.
>
> Alan Baljeu
> ________________________________
> From: Torbjörn Lager <[email protected]>
> To: Jan Wielemaker <[email protected]>
> Cc: "[email protected]" <[email protected]>
> Sent: Thursday, November 14, 2013 10:38:56 AM
> Subject: Re: [SWIPL] Aborting without killing
>
> Thanks Jan,
>
> Ah, ok I get it now. The reason I want to stop the execution of a goal
> (any goal) without killing the thread is that the dynamic db contains
> clauses declared as thread_local, and I don't want them to disappear.
>
> Best,
> Torbjörn
>
> On Thu, Nov 14, 2013 at 3:44 PM, Jan Wielemaker <[email protected]> wrote:
>> On 11/14/2013 01:44 PM, Torbjörn Lager wrote:
>>> Hi,
>>>
>>> Running (say)
>>>
>>> ?- repeat, fail.
>>>
>>> and executing thread_signal(main, abort) from another thread results in
>>>
>>> % Execution Aborted
>>>
>>> However, main is still running.
>>>
>>> However, running
>>>
>>> ?- thread_create((repeat, fail), ID, [alias(mymain)]).
>>>
>>> and executing thread_signal(mymain, abort) from another thread results
>>> in mymain terminating with an exception '$aborted'.
>>>
>>> So, is there a way to abort a currently running goal without also
>>> killing the thread that runs it? Or is the thread 'main' in the above
>>> example killed and then recreated again? Is that what is happening?
>>
>> The main thread runs the C-function PL_toplevel(), which restarts the
>> engine if it died on an exception.  This is the same for other exceptions:
>> an exception does not kill the interactive toplevel, but does kill any
>> other thread when not caught.
>>
>> What is special about abort, which is implemented as throw('$aborted'),
>> is that catch wraps the recover goal to re-throw the exception after
>> the recover goal has terminated.  So, you can cheat and make sure the
>> recover goal never terminates :-)
>>
>> The big question of course is why you'd like to use abort if you don't
>> want to kill the thread.  If you just want it stop the thread doing some
>> task and start another, simply do signal(Target, throw(stop)) and in the
>> target, you do
>>
>>        catch(Goal, stop, <whatever>)
>>
>>        Cheers --- Jan
>
>
>
> --
> Torbjörn Lager
> Professor of General and Computational Linguistics
> Department of Philosophy, Linguistics and Theory of Science
> University of Gothenburg
> Box 200, SE-405 30 Gothenburg, Sweden
> Phone: +46317864962
>
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>



-- 
Torbjörn Lager
Professor of General and Computational Linguistics
Department of Philosophy, Linguistics and Theory of Science
University of Gothenburg
Box 200, SE-405 30 Gothenburg, Sweden
Phone: +46317864962