enforce timeout in loop

semio has asked for the wisdom of the Perl Monks concerning the following question:

fellow monks

I would like to enforce a time-out for each element in an array as it is processed in a foreach loop. After a prescribed time limit, I would like to go to the next element in an array. To illustrate this, I have put together the following sample script.

#!/usr/bin/perl -w

use strict;
use POSIX qw/strftime/;

strftime "%H:%M:%S", localtime;
my @sleepvals = qw /1 2 3 4 5 6 7 8/;

print strftime "%H:%M:%S", localtime;
print "\n";
foreach my $sleepval (@sleepvals) {
sleep($sleepval);
print strftime "%H:%M:%S", localtime;
print "\n";
}
[download]

The output to this would look something like this:

01:03:39
01:03:40
01:03:42
01:03:45
01:03:49
01:03:54
01:04:00
01:04:07
01:04:15
[download]

I would like to enforce a time-out where, if sleep() takes longer than 3 seconds, sleep() is terminated, the rest of the foreach loop is processed and the script proceeds to the next element in the array. As an arbitrary example, I would like to set each iteration to, say 3 seconds, so the output would look as follows:

01:03:39
01:03:40
01:03:42
01:03:45
01:03:48
01:03:51
01:04:54
01:04:57
[download]

Thanks in advance for any suggestions.

cheers, -dave

Comment on enforce timeout in loop Select or Download Code

Replies are listed 'Best First'.
Re: enforce timeout in loop by perlmonkey (Hermit) on Sep 22, 2003 at 05:28 UTC
Follow the example in the perldoc page for alarm. Change your for loop to look like: `foreach my $sleepval (@sleepvals) { eval { local $SIG{ALRM} = sub { die }; alarm 3; sleep($sleepval); }; print strftime "%H:%M:%S", localtime; print "\n"; }` [download]	[reply] [d/l]
Re: Re: enforce timeout in loop by semio (Friar) on Sep 22, 2003 at 15:48 UTC
++perlmonkey. beautiful. This is exactly what I was looking for. cheers, -dave	[reply]
Re: enforce timeout in loop by Zaxo (Archbishop) on Sep 22, 2003 at 05:24 UTC
I think we need to know what kind of processing you're really doing on those array elements. Are you timing out a socket or some other IO handle or a child process? The timeout mechanism will differ for each. Socket flags, alarm, four-arg select, or kill/signal handling may be called for, but which depends on what you're doing. After Compline, Zaxo	[reply]
Re: enforce timeout in loop by rir (Vicar) on Sep 24, 2003 at 14:32 UTC
It sounds as if you know your maximum sleep time upfront. If this is the case you can: `# off hand code foreach my $sleepval ( @sleepvals) { sleep( $sleepval < $maxsleep ? $sleepval : $maxsleep); print strftime "%H:%M:%s", localtime; print "\n"; }` [download]	[reply] [d/l]


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