concurrency

name	concurrency
description	Use when: write or review concurrent code that avoids races, deadlocks, and shared-state bugs.

Goal: concurrent code that is correct first and fast second.

Use for:

• parallelizing work or handling many requests
• reviewing shared state, locking, and async flow
• diagnosing races, deadlocks, or corruption

Workflow:

1. Minimize shared mutable state; prefer message passing or immutability.
2. Define clear ownership of each mutable resource.
3. Protect shared state with the smallest necessary lock.
4. Acquire locks in a consistent order to avoid deadlock.
5. Set timeouts and cancellation on blocking operations.
6. Verify with stress tests and a race detector.

Patterns:

• immutable data shared freely without locks
• queues/channels to hand off work
• bounded concurrency to limit resource use
• idempotent operations for safe retries

Rules:

• share by communicating, or protect shared state explicitly
• keep critical sections tiny
• a consistent lock order prevents deadlocks
• never assume ordering; test under contention