I've found in CookBook recommendation to use two alarm(0) for handling timeouts, i.e instead of simple: 
eval {
  local $SIG{ALRM} = sub {die "alarm here"};
  alarm(5);
  long_code();
  alarm(0);
}

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use more complex: 
eval {
  local $SIG{ALRM} = sub {die "alarm here"};
  alarm(5);
  eval {
    long_code();
  };
  alarm(0);
  # see QUESTION 2 below
}
alarm(0); # see QUESTION 1 below
die if $@ && $@ !~ /alarm here/;

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I 100% agree with need of second internal eval if long_code can call die(). But I also have two questions:
  1. in which case first alarm(0) will not work and we will need to catch this and reset timer with second alarm(0)?
  2. look like there error in CookBook's example because we need to propagate error from internal eval by adding die $@ if $@; where I place comment "QUESTION 2" (maybe this error exists only in russian translation, not sure).
Update: exchanged alarm(0) and #QUES2 lines (just fix a typo).

In reply to second alarm(0) by powerman

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