● Verified by · firing 10 real concurrent requests (same technique as race-the-web)

ATM Cash-out Simulator

A live demo firing 10 real simultaneous $100 withdrawal requests against a $500 balance to reproduce the race condition, and showing how an atomic lock stops it.

Race Condition (TOCTOU) A gap exists between check and deduct

Withdrawals succeeded 0

Atomic Lock Applied Check+deduct as one operation

Withdrawals blocked 0