atelier/domains/concurrency/first-principles.md

Concurrency — First Principles

1. The Principles

P1. Immutability by Default

Mutable shared state is the enemy. The default is immutable; mutation is justified.

P2. Single Responsibility for Threads

Each unit of work has one owner. No "anyone can touch this" state.

P3. Boundaries are Locks

Synchronization happens at well-defined places. Lock scope is minimal and explicit.

P4. Determinism Over Speed

Correct concurrent code is faster than incorrect concurrent code. Race conditions are not "fast enough" — they are wrong.

P5. Lock Minimization

Locks are expensive and dangerous. Lock-free, wait-free, and message-passing are preferred where possible.

P6. No Silent Races

Race conditions are caught, not hidden. Tools (TSan, Go race detector) are part of CI.

P7. Cancellation Support

Every async operation can be cancelled. Cancellation is fast and complete.

P8. Timeout Discipline

Every blocking call has a timeout. Forever is not a duration.

P9. Bounded Queues

Unbounded queues are memory leaks in disguise. Bounded queues expose backpressure.

P10. Test for Race Conditions

Concurrent code is tested under concurrent load, not just happy-path correctness.