tree 01586beeeaa35c7b9debd95342bdde47e41bea52
parent e7141c64d1d3afadff05331d1e4cc95f6ce40a54
author Gilad Arnold <garnold@chromium.org> 1406137519 -0700
committer chrome-internal-fetch <chrome-internal-fetch@google.com> 1413596265 +0000

update_engine: UM: Incorporate backoff logic in UpdateCanStart.

This change adds backoff computation logic to UpdateCanStart. For the
most part, it is extending a private policy call (UpdateDownloadUrl) to
account for previously enacted backoff periods and to compute new ones
when an update failure is identified (accordingly, it is now called
UpdateBackoffAndDownloadUrl).

To conform with the pure nature of policy implementations, yet
minimizing the amount of "state" that needs to be managed and persisted
by the updater, we now consider download errors in bulks defined by the
most recent update failure (namely, the point in time when all URLs
where tried and failed). The updater is expected to keep track of the
update failure count, setting it to zero when a new update is seen, and
incrementing it (and recording the time it was incremented) when told to
do so by the policy. We therefore make some adjustments to the policy
API and its usage semantics.

BUG=chromium:396148
TEST=Unit tests.

Change-Id: If8787b8c41055779945f9b41368ec08ac5e6fcca
Reviewed-on: https://chromium-review.googlesource.com/210702
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>