>perl lockdemo.pl
locker: flock LOCK_EX
locker: locked
locker: sleep 10
main: alarm 5
main: flock LOCK_EX                          ### The lock is acquired here
main: timeout at lockdemo.pl line 30.        ### before the timeout occurs.

main: 5 seconds have passed
locker: flock LOCK_UN
locker: unlocked

##</code><code>##

sub locker
{
    my $start=time();
    open my $h,'>>','tempfile.tmp';
    say 'locker: flock LOCK_EX';
    flock($h,LOCK_EX);
    say 'locker: locked';
    say 'locker: sleep 10';
    sleep 10;
    say 'locker: flock LOCK_UN';
    flock($h,LOCK_UN);
    say 'locker: unlocked';
    close $h;
    my $stop=time();
    say 'locker ran for ',$stop-$start,' seconds';
}

##</code><code>##

>perl lockdemo-timed.pl
locker: flock LOCK_EX
locker: locked
locker: sleep 10
main: alarm 5
main: flock LOCK_EX
main: timeout at lockdemo-timed.pl line 30.

main: 5 seconds have passed
locker: flock LOCK_UN
locker: unlocked
locker ran for 10 seconds

>

##</code><code>##

H:\tmp\lockdemo>perl lockdemo-timed.pl
locker: flock LOCK_EX
locker: locked
locker: sleep 10
main: alarm 5
main: flock LOCK_EX
locker: flock LOCK_UN
main: alarm 0
main: successfully locked
main: 9 seconds have passed
locker: unlocked
locker ran for 10 seconds

H:\tmp\lockdemo>

##</code><code>##

sub locker
{
        $SIG{'ALRM'}='IGNORE';
        my $start=time();
        open my $h,'>>','tempfile.tmp';
        say 'locker: flock LOCK_EX';
        flock($h,LOCK_EX);
        say 'locker: locked';
        say 'locker: sleep 10 using select';
        select(undef,undef,undef,10);
        say 'locker: flock LOCK_UN';
        flock($h,LOCK_UN);
        say 'locker: unlocked';
        close $h;
        my $stop=time();
        say 'locker ran for ',$stop-$start,' seconds';
}

##</code><code>##

>perl lockdemo-select.pl
locker: flock LOCK_EX
locker: locked
locker: sleep 10 using select
main: alarm 5
main: flock LOCK_EX
main: timeout at lockdemo-select.pl line 30.

main: 5 seconds have passed
locker: flock LOCK_UN
locker: unlocked
locker ran for 10 seconds

>

##</code><code>##

H:\tmp\lockdemo>perl lockdemo-select.pl
locker: flock LOCK_EX
locker: locked
locker: sleep 10 using select
main: alarm 5
main: flock LOCK_EX
locker: flock LOCK_UN
main: alarm 0
main: successfully locked
main: 9 seconds have passed
locker: unlocked
locker ran for 10 seconds

H:\tmp\lockdemo>


##</code><code>##

sub locker
{
    $SIG{'ALRM'}=sub { warn "*** ALARM ***" };
    my $start=time();
    open my $h,'>>','tempfile.tmp';
    say 'locker: flock LOCK_EX';
    flock($h,LOCK_EX);
    say 'locker: locked';
    say 'locker: sleep 10 using select';
    select(undef,undef,undef,10);
    say 'locker: flock LOCK_UN';
    flock($h,LOCK_UN);
    say 'locker: unlocked';
    close $h;
    my $stop=time();
    say 'locker ran for ',$stop-$start,' seconds';
}


##</code><code>##

>perl lockdemo-signal.pl
locker: flock LOCK_EX
locker: locked
locker: sleep 10 using select
main: alarm 5
main: flock LOCK_EX
main: timeout at lockdemo-signal.pl line 30.

main: 5 seconds have passed
locker: flock LOCK_UN
locker: unlocked
locker ran for 10 seconds

>