ctdb shortcut locking

[tridge at samba.org]

Volker,

 > And what about the situation where very many children are
 > waiting for a lock? The child sits in F_WRLCK with SETLKW,
 > it gets the lock, it has to free it by exiting. Then there's
 > a window where the lock is free, and I think it is far from
 > clear that the parent ever gets the chance to try the SETLK
 > because other children are sitting there in SETLKW. I might
 > be wrong, but I would like to understand that situation.

yes, but it seems to be fine in practice. You can simulate N children
contending as fast as they can on one lock using the -n option to the
test prog. I'm pretty happy with how it performs, even though it can
loop more than once in the most heavily contended case.

Cheers, Tridge