> ## Documentation Index
> Fetch the complete documentation index at: https://committ.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Sync Lock Mutex

> Singleton Promise-chain mutex serializing all database writes.

# Sync Lock Mutex

The SyncLock (lib/sync-lock.ts) is a singleton Promise-chain mutex that serializes all database writes and hardware alarm sync triggers.

***

## Why It Exists

SQLite via expo-sqlite is a single-writer database. If Background Hydration and a User Saga attempt concurrent transactions, the native bridge throws SQLITE\_BUSY or SQLITE\_LOCKED errors.

***

## How It Works

Operations are chained onto a single Promise. Each caller waits for all preceding callers to finish:

```typescript theme={null}
const result = await syncLock.execute(
  "Saga:CreateCommitment",
  async () => { /* database writes */ },
  15_000 // timeout
);
```

***

## Timeout Circuit Breaker

Every lock holder has a hard time limit (default: 30 seconds). If exceeded, the lock is forcibly released via Promise.race. The timed-out operation's result is silently discarded.

***

## Manual Resync Awareness

The isManualResyncActive flag prevents HydrationSync from fighting the Manual Resync saga for the lock, breaking the "Loop of Doom" deadlock pattern.

***

## Cold Boot Reset

On app startup, syncLock.reset() clears any stale state from a prior crash. Required for Android ROMs that keep the process alive after swipe-kill when an Accessibility Service is active.