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eval EXPR with maximum execution time?
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Subject Author Date
eval EXPR with maximum execution time? alx__21 02-06-2008
Posted by alx__21 on February 6, 2008, 3:40 pm
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 Hi,

I'm looking for something that is like eval in that it can compile and
run code from strings, but will quit after a maximum given time.

The benchmark module tool "timethis" is very close, but it can only
ever specify a minimum time to iterate the given code. What I want is
code that iterates ONCE, breaking at a maximum time that I can specify
(if it runs that long).

If anybody knows of a function to do this I would appreciate it. I
would rather not have to start digging around in the source for
timethis to create my own.

Thanks.

Posted by Joost Diepenmaat on February 6, 2008, 3:47 pm
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 alx__21@hotmail.com writes:

> Hi,
>
> I'm looking for something that is like eval in that it can compile and
> run code from strings, but will quit after a maximum given time.
>
> The benchmark module tool "timethis" is very close, but it can only
> ever specify a minimum time to iterate the given code. What I want is
> code that iterates ONCE, breaking at a maximum time that I can specify
> (if it runs that long).
>
> If anybody knows of a function to do this I would appreciate it. I
> would rather not have to start digging around in the source for
> timethis to create my own.
>
> Thanks.

See perldoc -f alarm, but note that your code may still block on IO, as
far as I know, if your perl was build with "safe signals" - the default
for a few years now.

Joost.


Posted by Joost Diepenmaat on February 6, 2008, 3:50 pm
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> See perldoc -f alarm, but note that your code may still block on IO, as
> far as I know, if your perl was build with "safe signals" - the default
> for a few years now.
>
> Joost.

For a possibly more robust (or at least, more certain way of stopping
processing) you could fork() the offending process and kill() it from
the parent if it doesn't stop after a sleep().

If you want to get any useful data back from the fork()ed child process,
you need some kind of IPC. See the perlopen and perlipc man pages.

Joost.

Posted by Ben Morrow on February 6, 2008, 4:48 pm
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> > See perldoc -f alarm, but note that your code may still block on IO, as
> > far as I know, if your perl was build with "safe signals" - the default
> > for a few years now.

Using POSIX::SigAction it is possible to install an unsafe handler for
SIGALARM, which will allow you to break out of IO. Of course, all the
traditional caveats about unsafe signals then apply: it would be best to
do nothing more in the sighandler than die to break out of the eval.

> For a possibly more robust (or at least, more certain way of stopping
> processing) you could fork() the offending process and kill() it from
> the parent if it doesn't stop after a sleep().
>
> If you want to get any useful data back from the fork()ed child process,
> you need some kind of IPC. See the perlopen and perlipc man pages.

If you make the child the watchdog instead, there's no need for this. It
also makes it easier to clean up after a successful completion. Of
course, it makes it slightly *harder* to clean up after an unsuccessful
completion: you're pretty much back to signalling the parent, catching
that signal unsafely, and breaking out of the eval. See above :). If
you're not using alarm for anything else (on many systems, sleep uses
alarm internally) it is probably the best solution.

Ben


Posted by alx__21 on February 6, 2008, 4:54 pm
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Thank you!
As I'm not doing any IO inside the eval (just a simple return at the
end), I think that alarm will work well.

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