fix(memcached): panic on send on closed channel.
#7817
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Our memcached client has race between closing `inputCh` and submitting work to it (writing to channel) by different goroutines. This PR fix it by having `closed` channel to track if `inputCh` is closed and make it visible to other writter go-routines. Before: ``` === RUN TestMemcached_fetchKeysBatched panic: send on closed channel goroutine 29 [running]: github.com/grafana/loki/pkg/storage/chunk/cache.(*Memcached).fetchKeysBatched.func1() /home/kavirajk/src/loki/pkg/storage/chunk/cache/memcached.go:167 +0x87 created by github.com/grafana/loki/pkg/storage/chunk/cache.(*Memcached).fetchKeysBatched /home/kavirajk/src/loki/pkg/storage/chunk/cache/memcached.go:164 +0x165 FAIL github.com/grafana/loki/pkg/storage/chunk/cache 0.015s FAIL ``` After: ``` loki$ go test -v ./pkg/storage/chunk/cache/... -run TestMemcached_fetchKeysBatched === RUN TestMemcached_fetchKeysBatched --- PASS: TestMemcached_fetchKeysBatched (0.00s) PASS ok github.com/grafana/loki/pkg/storage/chunk/cache 0.013s ``` Signed-off-by: Kaviraj <kavirajkanagaraj@gmail.com>
Signed-off-by: Kaviraj <kavirajkanagaraj@gmail.com>
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Signed-off-by: Kaviraj <kavirajkanagaraj@gmail.com>
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Follow up to #7817 This PR uses `default` branch instead of `inputCh <- work` to make sure we are writing to closed `inputCh`. Signed-off-by: Kaviraj <kavirajkanagaraj@gmail.com>
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) Signed-off-by: Kaviraj <kavirajkanagaraj@gmail.com> **What this PR does / why we need it**: Follow up to #7817 This PR uses `default` branch instead of `inputCh <- work` to make sure we are writing to closed `inputCh`. Gist is, `default` run [only when none of the branch is ready](https://go.dev/tour/concurrency/6). which makes more sense rather than to have `inputCh <- work` (writing to closed channel on the branch condition) These can be explained by these two tiny snippets. * [with `default`](https://go.dev/play/p/-FspbTZd20I) * [without `default`](https://go.dev/play/p/Ag4WznOaEq0) **Which issue(s) this PR fixes**: Fixes #NA **Special notes for your reviewer**: We already have test `TestMemcached_fetchKeysBatched` to catch this behaviour. In fact this test caught this probabilistic behaviour in some CI failures. [here ](https://drone.grafana.net/grafana/loki/17853/3/4) and[ here](https://drone.grafana.net/grafana/loki/17854/3/4) Thanks @DylanGuedes for catching this CI failures. **Checklist** Signed-off-by: Kaviraj <kavirajkanagaraj@gmail.com>
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What this PR does / why we need it:
Our memcached client has race between closing
inputChand submitting work to it (writing to channel) by different goroutines.This PR fix it by having
closedchannel to track ifinputChis closed and make it visible to other writter go-routines.Before:
After:
Which issue(s) this PR fixes:
Fixes #
Special notes for your reviewer:
Found this panic on lots of internal Loki prod clusters.
Checklist
CHANGELOG.mdupdated