Perl Script reopens the file in the signal handler

Question

I have this perl script:

#!/bin/perl
use strict;
use warnings;
use Time::HiRes qw(usleep);
my $fd;
sub reopen {
    open $fd, ">>", "file.log" or die $!;
}
$SIG{USR1} = \&reopen;
reopen();
while(1){
    syswrite $fd, time . " ($$): message\n";
    usleep(100000);
}

I reopen file handle in the signal handler. Is it safe?

Answer 1

Yes^[1]. Since 5.8.1, the actual signal handler simply sets a flag saying a signal was received^[2]. That flag is checked between statements. System calls (e.g. usleep) return with error $!{EINTR} when interrupted by a signal, allowing the flag to be checked.

The signal will interrupt usleep, and reopen will be called before the next statement (syswrite^[3]) is evaluated.

---

1. Well, you might want to do local ($!, $^E); in case the interrupted code uses these.
2. Unless you disable "safe signals".
3. Why are you using syswrite instead of print? Is it to avoid buffering? Use $fd->autoflush(1); to do that.