Overview
- Bug Type:
- Event-order race
- Category:
- Concurrency, Async & Events
Definition
Logic assumes a specific order of asynchronous events; alternate orderings break invariants (TOCTOU).
How to fix Event-order race?
Combine check-and-use atomically; use optimistic concurrency with retries; serialize critical steps; verify ordering guarantees
Symptoms
Observable signs that may indicate Event-order race:
- Check-then-act logic fails when state changes between operations.
- Validation passes but subsequent use sees different state.
- Time-of-check/time-of-use windows exploited in tests.
Example Errors:
- Precondition failed due to state change
- Resource modified since validation
- TOCTOU violation