>env - perl interrupted.pl
Sun May 24 20:24:11 2015 pid=31389: main starts
Sun May 24 20:24:11 2015 pid=31389: main waiting for helper to lock
Sun May 24 20:24:11 2015 pid=31390: helper starts
Sun May 24 20:24:12 2015 pid=31389: main flock
SIGALRM in main at interrupted.pl line 16.
Sun May 24 20:24:17 2015 pid=31389: main can't lock: Interrupted system call (error code 4)
Sun May 24 20:24:17 2015 pid=31389: main flock done
Sun May 24 20:24:17 2015 pid=31389: main ends
Sun May 24 20:24:21 2015 pid=31390: helper ends

>env - PERL_SIGNALS=unsafe perl interrupted.pl
Sun May 24 20:24:39 2015 pid=31396: main starts
Sun May 24 20:24:39 2015 pid=31396: main waiting for helper to lock
Sun May 24 20:24:39 2015 pid=31397: helper starts
Sun May 24 20:24:40 2015 pid=31396: main flock
SIGALRM in main at interrupted.pl line 16.
Sun May 24 20:24:49 2015 pid=31397: helper ends
Sun May 24 20:24:49 2015 pid=31396: main flock done
Sun May 24 20:24:49 2015 pid=31396: main ends

alex@enterprise pts/0 20:24:49
/home/alex/tmp/lockdemo>