$ blog / engineering

Engineering

Lessons from what I run into at work, learned from and written down.

Series

Series · 5 parts Jul 2026

Making Login Thread-Safe

A production race condition taught four lessons about locks, atomicity, and safe publication.

00 Making Login Thread-Safe: Four Concurrency Lessons Learned (overview) 01 A Mutex Only Provides ACID's Isolation, Not the Rest 02 Finish First, Then Publish: The Safe Publication Pattern 03 Python's `with lock:` Guarantees Release on Exception 04 Double-Checked Locking: Two Checks, Two Different Jobs