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typescript.race_condition

Correctness High

Detects potential race conditions in asynchronous code.

Why It Matters

Race conditions:

Data corruption — Concurrent updates overwrite each other
Inconsistent state — Operations interleave unpredictably
Hard to reproduce — Bugs appear randomly

Example

// ❌ Before (race condition)
let balance = 0;

async function withdraw(amount: number): Promise<void> {
  if (balance >= amount) {
    await delay(10); // Simulates async DB call
    balance -= amount; // Another call might have changed balance!
  }
}

// ✅ After (with mutex/lock)
import { Mutex } from 'async-mutex';

const balanceMutex = new Mutex();
let balance = 0;

async function withdraw(amount: number): Promise<void> {
  await balanceMutex.runExclusive(async () => {
    if (balance >= amount) {
      await delay(10);
      balance -= amount;
    }
  });
}

What Unfault Detects

Shared state modified in async functions
Check-then-act patterns without locks
Concurrent array/object mutations