perl - Signal handler not working with double eval -


i have code timeout long-running process (sleep in case):

#!/usr/bin/env perl use strict; use warnings;  die "usage: $0 sleep timeout\n" unless @argv == 2; ( $sleep, $timeout ) = @argv;  $|++;  eval {     local $sig{alrm} = sub { die "timeout\n" };     alarm $timeout;      eval {         # long-running process         print "going sleep ... ";         sleep $sleep;         print "done\n";     };        alarm 0;    # cancel timeout };    die $@ if $@;

when run ./alarm 5 2, expect die saying "timeout". exits 0 , says nothing. works expected when remove inner eval block (not block's content, eval) though. can explain why that? thanks.

because trap error in first eval block , second eval block not have exception , clears $@.

eval {     local $sig{alrm} = sub { die "timeout\n" };     alarm $timeout;      eval {         # long-running process         print "going sleep ... "; a:      sleep $sleep;         print "done\n";     };   b:      alarm 0;    # cancel timeout c:};    die $@ if $@;

$sleep > $timeout, @ a: program throws sigalrm. signal caught local signal handler , calls die "timeout\n". perl sets $@ "timeout\n" , resumes execution @ b:. program makes c: without additional errors. since outer eval block completed normally, perl clears $@, , final die statement not execute.

to seems want do, either

  1. don't use eval on outer block
  2. put die $@ if $@ call @ end of outer block

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