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>perl lockdemo.pl
locker: flock LOCK_EX
locker: locked
...
main: 5 seconds have passed
locker: flock LOCK_UN
locker: unlocked

sub locker
{
    my $start=time();
...
    my $stop=time();
    say 'locker ran for ',$stop-$start,' seconds';
}

>perl lockdemo-timed.pl
locker: flock LOCK_EX
locker: locked
...
locker ran for 10 seconds

>

H:\tmp\lockdemo>perl lockdemo-timed.pl
locker: flock LOCK_EX
locker: locked
...
locker ran for 10 seconds

H:\tmp\lockdemo>

sub locker
{
        $SIG{'ALRM'}='IGNORE';
...
        my $stop=time();
        say 'locker ran for ',$stop-$start,' seconds';
}

>perl lockdemo-select.pl
locker: flock LOCK_EX
locker: locked
...
locker ran for 10 seconds

>

H:\tmp\lockdemo>perl lockdemo-select.pl
locker: flock LOCK_EX
locker: locked
...
locker ran for 10 seconds

H:\tmp\lockdemo>

sub locker
{
    $SIG{'ALRM'}=sub { warn "*** ALARM ***" };
...
    my $stop=time();
    say 'locker ran for ',$stop-$start,' seconds';
}

>perl lockdemo-signal.pl
locker: flock LOCK_EX
locker: locked
...
locker ran for 10 seconds

>