Re: [igraph] igraph/C: is there a facility for interrupting computations?

[Szabolcs Horvát]

Hi Tamás,

Thanks for the quick response!
I just tried this and with igraph_set_interruption_handler() it works
great (already integrated with Mathematica).

Szabolcs

On 29 August 2015 at 23:03, Tamas Nepusz <address@hidden> wrote:
> Hi Szabolcs,
>
> Not all igraph routines support interruptions, but those that do call
> a macro named IGRAPH_ALLOW_INTERRUPTION() at regular intervals. This
> macro will in turn call a so-called interruption handler, which you
> can set with the igraph_set_interruption_handler() function (see
> https://github.com/igraph/igraph/blob/master/src/interrupt.c). Within
> the interruption handler, you must check whether the host environment
> (Mathematica in your case) has signalled that the user wishes to
> interrupt the computation. (For instance, in Python, I call the
> PyErr_CheckSignals() function here). If the user wishes to interrupt
> the computation, you must call IGRAPH_FINALLY_FREE() and then return
> IGRAPH_INTERRUPTED; otherwise return IGRAPH_SUCCESS. See the Python
> interface for an example:
>
> https://github.com/igraph/python-igraph/blob/master/src/igraphmodule.c#L147
>
> I'm not sure how this translates to Mathematica - ideally, Mathematica
> should have some kind of an internal flag that is set when the user
> wishes to interrupt the computation. Your task would be to check this
> flag whenever the interrupt handler is called.
>
> T.
>
> T.
>
>
> On Sat, Aug 29, 2015 at 10:28 PM, Szabolcs Horvát <address@hidden> wrote:
>> Dear All,
>>
>> Does the C interface to igraph have any facility for
>> aborting/interrupting computations that take very long?
>>
>> I assume it does because interrupting is possible with igraph/R.  E.g.
>> the following takes a long time:
>>
>> rewire(erdos.renyi.game(1000, 0.5, 'gnp'), keeping_degseq(niter=10000000))
>>
>> But pressing the stop button in R cancels it without killing the R session.
>>
>> How is this implemented?
>>
>> So far I tried setting a status handler as follows:
>>
>> int igStatusHandler(const char *, void *) { return IGRAPH_INTERRUPTED; }
>>
>> igraph_set_status_handler(igStatusHandler);
>>
>> But igraph_rewire() still runs to the finish without interruption.
>>
>> Use case: I am working on a (partial) Mathematica interface and the
>> ability to interrupt would be a big usability improvement.  I was
>> using igraph through the R interface from Mathematica before
>> (https://github.com/szhorvat/IGraphR) but that has its limitations.
>>
>> Szabolcs
>>
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