state: safer entity watchers

state: safer entity watchers

Entity watchers now always take a fresh copy of the entity to send down the
channel. This is:

* safer, because we're no longer sending the originating entity off down a
  channel to who-knows-where while still keeping the originating reference,
  potentially in use;
* better, because it means that the initial event is a snapshot of *current*
  state, rather than just whatever state the Watch()ed entity had (which may
  be very out of date; in, for example the Uniter); the original behaviour
  would generate very unhelpful sequences of events.

https://code.launchpad.net/~fwereade/juju-core/fix-entity-watchers/+merge/126190

(do not edit description out of merge proposal)

[fwereade, 2012-09-25 08:32:01]

Please take a look.

[rog, 2012-09-25 08:37:10]

On 2012/09/25 08:32:01, fwereade wrote:
> Please take a look.

LGTM++; i hadn't considered the thread-safe bit; makes sense.

[TheMue, 2012-09-25 08:38:49]

LGTM

[fwereade, 2012-09-25 08:56:34]

*** Submitted:

state: safer entity watchers

Entity watchers now always take a fresh copy of the entity to send down the
channel. This is:

* safer, because we're no longer sending the originating entity off down a
  channel to who-knows-where while still keeping the originating reference,
  potentially in use;
* better, because it means that the initial event is a snapshot of *current*
  state, rather than just whatever state the Watch()ed entity had (which may
  be very out of date; in, for example the Uniter); the original behaviour
  would generate very unhelpful sequences of events.

R=rog, TheMue
CC=
https://codereview.appspot.com/6571047