🏁 Race Conditions

A race condition happens when the correctness of your program depends on timing.

Typical pattern:

1. Thread A reads shared state
2. Thread B changes it
3. Thread A writes back using stale information

Even with the GIL, many multi-step operations ("read-modify-write") are not atomic.

---

✅ Classic Example: Shared Counter

Two threads both run:

counter = counter + 1

That statement is multiple bytecode operations: load, add, store. Another thread can interleave between those steps.

---

✅ Fixes

• Protect the critical section with threading.Lock
• Avoid shared mutable state (message passing, queue.Queue)
• Use higher-level primitives (thread-safe queues, executors)

---

🔍 Key Takeaways

• A race condition is a correctness bug, not just "weird behavior".
• If you share state, you need a strategy: lock, queue, or redesign.

---

Back: Module 12 README