Add independent config poller service.

Add independent config poller service.

Add a configuration poller service which triggers a callback when the
configuration's hash changes.

This will be used in follow-up CLs to replace other configuration
operations.

BUG=chromium:682465
TEST=None

Review-Url: https://codereview.chromium.org/2644413002
Committed: https://github.com/luci/luci-go/commit/b4bee637a6593dd2b8d67e96cbc31a515c61f38e

[dnj, 2017-01-20 23:39:53]

dnj@chromium.org changed reviewers:
+ iannucci@chromium.org

[dnj, 2017-01-20 23:39:53]

PTAL

[iannucci, 2017-01-21 00:09:13]

lgtm

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
File logdog/server/service/config/poller.go (right):

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
logdog/server/service/config/poller.go:20: // the OnChange function will be
called and the polling will stop.
what's the reason for having the loop stop on the first change?

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
logdog/server/service/config/poller.go:27: // if the configuration has changed.
If it has, KillFunc will be invoked.
something went wrong with this comment I think. Also KillFunc?

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
logdog/server/service/config/poller.go:45: if err := c.Err(); err != nil {
so remember that thing we talked about last feburary where we weren't sure if it
was safe to call Err without blocking on Done? Turns out that you're right:
https://github.com/golang/go/issues/14292

However, since clock.Sleep synchronizes with Done, this is actually ok. In fact,
I don't think you need this if statement at all (just let the clock.Sleep do it)

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
logdog/server/service/config/poller.go:86: D("configSet", p.ConfigSet).D("path",
p.Path).Err()
how would

  return errors.Annotate(err).
    Reason(...).
    D(...).
    D(...).
    Err()

Look?

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
File logdog/server/service/config/poller_test.go (right):

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
logdog/server/service/config/poller_test.go:96: Convey(`Will execute the kill
function if the configuration changes.`, func() {
kill function?

[dnj, 2017-01-21 01:17:54]

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
File logdog/server/service/config/poller.go (right):

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
logdog/server/service/config/poller.go:20: // the OnChange function will be
called and the polling will stop.
On 2017/01/21 00:09:12, iannucci wrote:
> what's the reason for having the loop stop on the first change?

The application will quit after this, so there's no point in continuing. I
suppose I might as well keep it going, though - the change function can just
cancel the Context.

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
logdog/server/service/config/poller.go:27: // if the configuration has changed.
If it has, KillFunc will be invoked.
On 2017/01/21 00:09:12, iannucci wrote:
> something went wrong with this comment I think. Also KillFunc?

Fixed.

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
logdog/server/service/config/poller.go:45: if err := c.Err(); err != nil {
On 2017/01/21 00:09:12, iannucci wrote:
> so remember that thing we talked about last feburary where we weren't sure if
it
> was safe to call Err without blocking on Done? Turns out that you're right:
> https://github.com/golang/go/issues/14292
> 
> However, since clock.Sleep synchronizes with Done, this is actually ok. In
fact,
> I don't think you need this if statement at all (just let the clock.Sleep do
it)

Done.

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
logdog/server/service/config/poller.go:86: D("configSet", p.ConfigSet).D("path",
p.Path).Err()
On 2017/01/21 00:09:12, iannucci wrote:
> how would
> 
>   return errors.Annotate(err).
>     Reason(...).
>     D(...).
>     D(...).
>     Err()
> 
> Look?

Taller, but sure.

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
File logdog/server/service/config/poller_test.go (right):

https://codereview.chromium.org/2644413002/diff/20001/logdog/server/service/c...
logdog/server/service/config/poller_test.go:96: Convey(`Will execute the kill
function if the configuration changes.`, func() {
On 2017/01/21 00:09:12, iannucci wrote:
> kill function?

Done.

[dnj, 2017-01-21 01:18:51]

The CQ bit was checked by dnj@chromium.org

[dnj, 2017-01-21 01:18:51]

The patchset sent to the CQ was uploaded after l-g-t-m from
iannucci@chromium.org
Link to the patchset: https://codereview.chromium.org/2644413002/#ps60001
(title: "interval -> period")

[commit-bot: I haz the power, 2017-01-21 01:18:59]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-01-21 01:26:14]

CQ is committing da patch.

Bot data: {"patchset_id": 60001, "attempt_start_ts": 1484961531140660,
"parent_rev": "46e4d75b7f41409c78bcd0c866120a49559440c3", "commit_rev":
"b4bee637a6593dd2b8d67e96cbc31a515c61f38e"}

[commit-bot: I haz the power, 2017-01-21 01:26:18]

Description was changed from

==========
Add independent config poller service.

Add a configuration poller service which triggers a callback when the
configuration's hash changes.

This will be used in follow-up CLs to replace other configuration
operations.

BUG=chromium:682465
TEST=None
==========

to

==========
Add independent config poller service.

Add a configuration poller service which triggers a callback when the
configuration's hash changes.

This will be used in follow-up CLs to replace other configuration
operations.

BUG=chromium:682465
TEST=None

Review-Url: https://codereview.chromium.org/2644413002
Committed:
https://github.com/luci/luci-go/commit/b4bee637a6593dd2b8d67e96cbc31a515c61f38e
==========

[commit-bot: I haz the power, 2017-01-21 01:26:19]

Committed patchset #4 (id:60001) as
https://github.com/luci/luci-go/commit/b4bee637a6593dd2b8d67e96cbc31a515c61f38e