cipd: shared tag cache

cipd: shared tag cache

Add -cache-dir flag to most of the commands: a path to a shared cache dir.
ATM only tag cache uses it.
In the next CL it will be used for a shared instance cache.

No synchronization between different cipd processes that access
same cache dir, because cipd never used locking

R=vadimsh@chromium.org
BUG=601017
Committed: https://github.com/luci/luci-go/commit/81ae6f3a3836e9f32c9d99398974d69bf382ff80

[nodir, 2016-04-08 01:24:33]

Description was changed from

==========
cipd: shared tag cache

Add -cache-dir flag to most of the commands: a path to a shared cache dir.
In the next CL it will be used for a shared instance cache.

No synchronization between different cipd processes that access the
same cache dir, because cipd never used locking

R=vadimsh@chromium.org
BUG=601017
==========

to

==========
cipd: shared tag cache

Add -cache-dir flag to most of the commands: a path to a shared cache dir.
ATM only tag cache uses it.
In the next CL it will be used for a shared instance cache.

No synchronization between different cipd processes that access
same cache dir, because cipd never used locking

R=vadimsh@chromium.org
BUG=601017
==========

[nodir, 2016-04-08 01:32:15]

PTAL. Tested locally.

[Vadim Sh., 2016-04-08 01:42:55]

https://codereview.chromium.org/1862303004/diff/20001/client/cmd/cipd/main.go
File client/cmd/cipd/main.go (right):

https://codereview.chromium.org/1862303004/diff/20001/client/cmd/cipd/main.go...
client/cmd/cipd/main.go:234: const cacheDirHelp = "Directory for shared cache.
CAVEAT: only one cipd process may access same cache dir simulatenously."
"CAVEAT: only one cipd process may access same cache dir simulatenously"

this is wrong

"no lock files" doesn't mean "no synchronization".

Currently, cache file is replaced atomically when closed. It means the state
will never be corrupted, even in case of concurrent access. The worst case is
some cache entries won't be bumped to the top of the list, it's not a big deal
(it's a cache after all), and it's not an oversight but conscious decision to
avoid lock files. Lock files is a can of worms (esp. across all three
platforms).

https://codereview.chromium.org/1862303004/diff/20001/client/cmd/cipd/main.go...
client/cmd/cipd/main.go:238: f.StringVar(&opts.cacheDir, "cache-dir", "",
cacheDirHelp)
keep help string inline, like in the rest options here

[nodir, 2016-04-08 11:19:48]

done

[Vadim Sh., 2016-04-08 19:13:50]

lgtm

[nodir, 2016-04-08 20:24:23]

The CQ bit was checked by nodir@chromium.org

[commit-bot: I haz the power, 2016-04-08 20:24:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1862303004/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1862303004/40001

[commit-bot: I haz the power, 2016-04-08 20:31:04]

Description was changed from

==========
cipd: shared tag cache

Add -cache-dir flag to most of the commands: a path to a shared cache dir.
ATM only tag cache uses it.
In the next CL it will be used for a shared instance cache.

No synchronization between different cipd processes that access
same cache dir, because cipd never used locking

R=vadimsh@chromium.org
BUG=601017
==========

to

==========
cipd: shared tag cache

Add -cache-dir flag to most of the commands: a path to a shared cache dir.
ATM only tag cache uses it.
In the next CL it will be used for a shared instance cache.

No synchronization between different cipd processes that access
same cache dir, because cipd never used locking

R=vadimsh@chromium.org
BUG=601017

Committed:
https://github.com/luci/luci-go/commit/81ae6f3a3836e9f32c9d99398974d69bf382ff80
==========

[commit-bot: I haz the power, 2016-04-08 20:31:05]

Committed patchset #3 (id:40001) as
https://github.com/luci/luci-go/commit/81ae6f3a3836e9f32c9d99398974d69bf382ff80