$ ./locktest & sleep 4; ./locktest
[1] 64228
Using flock()...
64228 shares.
64228 owns
64228 shares
Using flock()...
64233 shares.
64233 waiting for previous instance(s) to exit...
64228 leaving to allow new instance to run.
64233 owns
Running...
64233 owns
64233 shares
^C