state: update ServicesWatcher

state: update ServicesWatcher

Add lifecycle support to the ServicesWatcher and make it a new style
watcher that only returns service names.

https://code.launchpad.net/~aramh/juju-core/104-state-watchers-services5/+merge/128715

(do not edit description out of merge proposal)

[aram, 2012-10-09 13:46:42]

Please take a look.

[niemeyer, 2012-10-09 21:29:18]

Great stuff. LGTM with the same change as suggested for the others:

https://codereview.appspot.com/6640047/diff/1/state/watcher.go
File state/watcher.go (right):

https://codereview.appspot.com/6640047/diff/1/state/watcher.go#newcode378
state/watcher.go:378: // ServicesWatcher notifies about the lifecycle changes of
the services
s/of the services/for services/

https://codereview.appspot.com/6640047/diff/1/state/watcher.go#newcode416
state/watcher.go:416: err =
w.st.services.Find(nil).Select(lifeFields).All(&docs)
Iter fits better here also.

https://codereview.appspot.com/6640047/diff/1/state/watcher.go#newcode427
state/watcher.go:427: func (w *ServicesWatcher) merge(pending []string, name
string) (new []string, err error) {
I just realized something: if name is in pending, we can return from here,
without ever querying the database again. This will save unnecessary re-queries
while we're waiting for an event to be consumed.

https://codereview.appspot.com/6640047/diff/1/state/watcher.go#newcode437
state/watcher.go:437: return append(pending, name), nil
And then we don't need to check here (check is missing, and can stay like that).

https://codereview.appspot.com/6640047/diff/1/state/watcher.go#newcode446
state/watcher.go:446: for _, v := range pending {
And this loop can go away.

[aram, 2012-10-10 15:38:32]

*** Submitted:

state: update ServicesWatcher

Add lifecycle support to the ServicesWatcher and make it a new style
watcher that only returns service names.

R=niemeyer
CC=
https://codereview.appspot.com/6640047