cmd/jujud: wrap singular workers

cmd/jujud: wrap singular workers

We start the various workers that require only a single
instance to be running via the runner returned by singular.New.

This is awkward to test - we just do a basic sanity check
that the right workers are started through the singular
runner.

https://code.launchpad.net/~rogpeppe/juju-core/mfoord-wrapsingletonworkers/+merge/215035

(do not edit description out of merge proposal)

[rog, 2014-04-09 21:11:30]

Please take a look.

[rog, 2014-04-10 09:59:19]

Please take a look.

[natefinch, 2014-04-10 11:14:38]

LGTM with just a couple minor suggestions.

https://codereview.appspot.com/86200043/diff/40001/cmd/jujud/machine.go
File cmd/jujud/machine.go (right):

https://codereview.appspot.com/86200043/diff/40001/cmd/jujud/machine.go#newco...
cmd/jujud/machine.go:253: conn := singularAPIConn{st, st.Agent()}
could this code get moved to the loop over entity.jobs below?  It diesn't seem
to neec to be here, and it puts the declaration far from the use of the
variable.

https://codereview.appspot.com/86200043/diff/40001/cmd/jujud/machine_test.go
File cmd/jujud/machine_test.go (right):

https://codereview.appspot.com/86200043/diff/40001/cmd/jujud/machine_test.go#...
cmd/jujud/machine_test.go:384: c.Assert(s.singularRecord.started(),
jc.DeepEquals, []string{
This checks order of the slice, too, right?  Does the order matter?  If not, we
may want to use jc.SameContents here, so we don't fail the test if the order
changes.

[rog, 2014-04-10 11:38:21]

https://codereview.appspot.com/86200043/diff/40001/cmd/jujud/machine.go
File cmd/jujud/machine.go (right):

https://codereview.appspot.com/86200043/diff/40001/cmd/jujud/machine.go#newco...
cmd/jujud/machine.go:253: conn := singularAPIConn{st, st.Agent()}
On 2014/04/10 11:14:38, nate.finch wrote:
> could this code get moved to the loop over entity.jobs below?  It diesn't seem
> to neec to be here, and it puts the declaration far from the use of the
> variable.

i don't we can do this, because newSingularRunner can fail, and if that happens
we don't want to leave the other jobs running.

https://codereview.appspot.com/86200043/diff/40001/cmd/jujud/machine_test.go
File cmd/jujud/machine_test.go (right):

https://codereview.appspot.com/86200043/diff/40001/cmd/jujud/machine_test.go#...
cmd/jujud/machine_test.go:384: c.Assert(s.singularRecord.started(),
jc.DeepEquals, []string{
On 2014/04/10 11:14:38, nate.finch wrote:
> This checks order of the slice, too, right?  Does the order matter?  If not,
we
> may want to use jc.SameContents here, so we don't fail the test if the order
> changes.

the slice is sorted (see the implementation of the started method)