It's possible to terminate some varieties of infinite looping with alarm():

# setup an ALRM handler
my $timed_out = 0;
local $SIG{ALRM} = sub { die "Timed out!" };

# run some code for 10 seconds max
eval {
  alarm 10; # let it run 10 seconds
  eval($code);
  die $@ if $@;
};

# figure out if it got an alarm
warn "Alarm rang!" if $@ and $@ =~ /Timed out!/;
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However, an infinitely running regex would probably not get interupted here due to Perl's new safe-signals implementation which only looks for new signals between op-codes.

-sam