Concurrency — What Claude Gets Wrong

Your training data is overwhelmingly single-threaded. When you write concurrent code, you pattern-match on what concurrent code looks like instead of reasoning about interleavings. The result: code that works in tests and races in production.

The Three Questions

Before writing any concurrent code, answer:

1. What state is shared? — List every variable, struct field, or resource accessed by multiple tasks/threads.
2. Is every multi-step mutation atomic? — If two steps must happen together, they need a single lock or transaction.
3. What happens on cancellation? — If this task is cancelled mid-operation, is state consistent?

Anti-Patterns You Default To