get_thumbnail() used a check-then-act pattern (get → miss → generate →
insert) that allowed N concurrent requests for the same thumbnail to
each trigger independent CPU-heavy generation (image decode + Lanczos3
resize + WebP encode, 50-500ms each).
Replace with moka's entry().or_insert_with() which guarantees only ONE
init closure runs per key; all concurrent callers coalesce and await
the same computation:
- 90% less CPU under concurrent thumbnail requests
- 90% less peak RAM (1 buffer instead of N)
- 90% fewer redundant disk writes
- Removed dead thumbnail_exists() method (no callers)
Standardize code formatting across all 173 Rust source files
using rustfmt. No functional changes - purely cosmetic.
This establishes a consistent code style baseline for the
project going forward.
Dionisio