uniter: don't repeat change events

uniter: don't repeat change events

By putting the unit.ClearResolved onto the filter goroutine, and immediately
forcing unit-change handling, we can ensure that the uniter goroutine cannot
request a fresh resolved event before the filter has refreshed the unit and
determined that there is no event to deliver.

https://code.launchpad.net/~fwereade/juju-core/uniter-no-repeat-resolved/+merge/169618

(do not edit description out of merge proposal)

[fwereade, 2013-06-15 11:48:45]

Please take a look.

[dave_cheney.net, 2013-06-17 07:45:42]

LGTM. Thank you.

https://codereview.appspot.com/10298043/diff/1/worker/uniter/filter.go
File worker/uniter/filter.go (right):

https://codereview.appspot.com/10298043/diff/1/worker/uniter/filter.go#newcod...
worker/uniter/filter.go:104: didSetCharm:       make(chan struct{}),
i see below there is a `nothing` helper, would making these declarations
didSetCharm make(chan nothing), 
add anything, or is it just rearranging deck chairs ?

[mue, 2013-06-18 10:50:25]

LGTM, only small comment.

https://codereview.appspot.com/10298043/diff/1/worker/uniter/filter.go
File worker/uniter/filter.go (right):

https://codereview.appspot.com/10298043/diff/1/worker/uniter/filter.go#newcod...
worker/uniter/filter.go:104: didSetCharm:       make(chan struct{}),
On 2013/06/17 07:45:43, dfc wrote:
> i see below there is a `nothing` helper, would making these declarations
> didSetCharm make(chan nothing), 
> add anything, or is it just rearranging deck chairs ?

nothing is the instance of a struct{}. How about

type SignalChan chan struct{}
var Signal = struct{}{}

in package util?

[fwereade, 2013-06-19 13:14:27]

https://codereview.appspot.com/10298043/diff/1/worker/uniter/filter.go
File worker/uniter/filter.go (right):

https://codereview.appspot.com/10298043/diff/1/worker/uniter/filter.go#newcod...
worker/uniter/filter.go:104: didSetCharm:       make(chan struct{}),
On 2013/06/18 10:50:25, mue wrote:
> On 2013/06/17 07:45:43, dfc wrote:
> > i see below there is a `nothing` helper, would making these declarations
> > didSetCharm make(chan nothing), 
> > add anything, or is it just rearranging deck chairs ?
> 
> nothing is the instance of a struct{}. How about
> 
> type SignalChan chan struct{}
> var Signal = struct{}{}
> 
> in package util?

Interesting idea, especially in light of the NotifyWatcher stuff I recently
merged... those should perhaps be SignalWatchers? I'll let it marinade a bit.

https://codereview.appspot.com/10298043/diff/1/worker/uniter/filter.go#newcod...
worker/uniter/filter.go:104: didSetCharm:       make(chan struct{}),
On 2013/06/17 07:45:43, dfc wrote:
> i see below there is a `nothing` helper, would making these declarations
> didSetCharm make(chan nothing), 
> add anything, or is it just rearranging deck chairs ?

Thanks, but I think `var nothing = struct{}{}` is more useful than `type nothing
struct{}`; and if I were to name both of them I think it'd end up uglier. So
I'll stick with this for now.