When using `Discourse.cache.fetch` with an expiry, there's a potential for a race condition due to how we read the data from redis.
The code used to be
```ruby
raw = redis.get(key) if !force
entry = read_entry(key) if raw
return entry if raw && !(entry == :__corrupt_cache__)
```
with `read_entry` defined as follow
```ruby
def read_entry(key)
if data = redis.get(key)
Marshal.load(data)
end
rescue => e
:__corrupt_cache__
end
```
If the value at "key" expired in redis between `raw = redis.get` and `entry = read_entry`, the `entry` variable would be `nil` despite `raw` having a value.
We would then proceed to return `entry` (which is `nil`) thinking it had a value, when it didn't.
The first `redis.get` can be skipped altogether and we can rely only on `read_entry` to read the data from redis. Thus avoiding the race condition and removing the double read operations.
Internal ref - t/132507
d5cd669464