state: WatchMachines should watch the topology, not the zk children

state: WatchMachines should watch the topology, not the zk children

TODO: there is still to much string munging going on here, I will 
open a branch to define equality for *Machines which will reduce
the stringyness a bit.

https://code.launchpad.net/~dave-cheney/juju/go-watch-machines-topology/+merge/106294

(do not edit description out of merge proposal)

[dave_cheney.net, 2012-05-21 08:37:35]

Please take a look.

[niemeyer, 2012-05-21 19:59:32]

LGTM with a few minors handled:

https://codereview.appspot.com/6210066/diff/5001/state/watcher.go
File state/watcher.go (right):

https://codereview.appspot.com/6210066/diff/5001/state/watcher.go#newcode297
state/watcher.go:297: // in the topology.
The original comment was more sensible. There's no such thing as "a topology"
for users of the state package. Again, ZooKeeper is an implementation detail. It
should remain behind that API as much as possible.

https://codereview.appspot.com/6210066/diff/5001/state/watcher.go#newcode304
state/watcher.go:304: topology   *topology
Do we need a whole topology? Isn't this enough:

    knownMachineKeys []string

https://codereview.appspot.com/6210066/diff/5001/state/watcher.go#newcode386
state/watcher.go:386: // diff returns a tupple of entries that exist in the
previous
This function isn't worth it. Just call except twice above.

https://codereview.appspot.com/6210066/diff/5001/state/watcher.go#newcode393
state/watcher.go:393: func except(A, B []string) (missing []string) {
This is actually what "difference" means set-wise (it's A - B) so diff would be
a good name here.

[dave_cheney.net, 2012-05-22 01:09:17]

Please take a look.

https://codereview.appspot.com/6210066/diff/5001/state/watcher.go
File state/watcher.go (right):

https://codereview.appspot.com/6210066/diff/5001/state/watcher.go#newcode297
state/watcher.go:297: // in the topology.
On 2012/05/21 19:59:32, niemeyer wrote:
> The original comment was more sensible. There's no such thing as "a topology"
> for users of the state package. Again, ZooKeeper is an implementation detail.
It
> should remain behind that API as much as possible.

Done.

https://codereview.appspot.com/6210066/diff/5001/state/watcher.go#newcode304
state/watcher.go:304: topology   *topology
Certainly, done.

https://codereview.appspot.com/6210066/diff/5001/state/watcher.go#newcode386
state/watcher.go:386: // diff returns a tupple of entries that exist in the
previous
On 2012/05/21 19:59:32, niemeyer wrote:
> This function isn't worth it. Just call except twice above.

Done.

https://codereview.appspot.com/6210066/diff/5001/state/watcher.go#newcode393
state/watcher.go:393: func except(A, B []string) (missing []string) {
On 2012/05/21 19:59:32, niemeyer wrote:
> This is actually what "difference" means set-wise (it's A - B) so diff would
be
> a good name here.

Done.

[dave_cheney.net, 2012-05-22 01:14:54]

*** Submitted:

state: WatchMachines should watch the topology, not the zk children

TODO: there is still to much string munging going on here, I will 
open a branch to define equality for *Machines which will reduce
the stringyness a bit.

R=niemeyer
CC=
https://codereview.appspot.com/6210066