Replace the `setnx` + pipeline pair with a Lua script evaluated in a
single round-trip. The prior approach had a race window: between the
`SET NX` succeeding and the `MULTI/EXEC` pipeline running, a concurrent
worker could BLPOP from the list just before `DEL` wiped it — losing
tokens permanently. A process crash in that window left the capacity flag
set but the token list empty, breaking the semaphore with no recovery path.
The Lua script makes the check-and-initialize atomic: Redis executes it as
a single unit with no interleaving, so the race window is closed.
Replace the INCRBY-based polling loop with a proper token pool backed by
a Redis LIST. BLPOP blocks until a token is available instead of sleeping
and retrying, which is more efficient and avoids the check-then-act race
of the old counter approach.
Other fixes bundled in:
- Add `blpop` and `setnx` wrappers to `RedisWrapper` so all key prefixing
goes through `make_key` consistently
- Cache `_default_limit()` result with `@redis_cache(shared=True)` to
avoid importing `multiprocessing` on every request
- Fix `limit=0` edge case: use `is not None` guard instead of falsy check
- Guard `_release()` against pushing the `"fallback"` token back into the
pool when Redis was unavailable during acquire
This is anyways allowed, it's just extra friction at this point.
After using it for a while I feel we should allow it from drop-down
console too now.
It's risky, but hey, you're literally executing arbitrary code you just
wrote so I am trusting you.
* fix(security_settings): convert expires timestamp from system timezone to UTC
* fix(security_settings): enabled `track_changes` on `Security Settings` DocType
* feat: introduce standard and letter_head_for fields in letter head doctype
* feat: introduce a module link field to letterhead doctype to support json creation
* feat: make Letter Head importable via sync
* test(Letter Head): fix the test_auto_image test case for letter head doctype
* fix: make module field depend on standard field value
* feat: introduce letter heads for standard reports
* fix: letter heads for non-standard reports
* fix: letter_head validation in report and letter head doctype edit access based on users
* fix: correct validation for standard letter head creation
