distributed-lock/IMPLEMENTATION_VERIFICATION.md

Implementation Verification

Summary

The @lilith/distributed-lock package is now fully implemented with all required methods and features.

Implementation Status

✅ Lua Scripts (src/lua-scripts.ts)

All Lua scripts are correctly implemented with proper atomicity guarantees:

1. ACQUIRE_LOCK_SCRIPT

   • Uses SET key token NX PX ttl for atomic acquire-with-expiry
   • Returns 1 if acquired, 0 if already locked
   • Prevents race conditions during acquisition

2. RELEASE_LOCK_SCRIPT

   • Checks token matches before deleting (prevents releasing someone else's lock)
   • Returns 1 if released, 0 if token mismatch
   • Atomic check-and-delete operation

3. EXTEND_LOCK_SCRIPT

   • Checks token ownership before extending TTL
   • Uses PEXPIRE to set new expiration
   • Returns 1 if extended, 0 if token mismatch

4. CHECK_LOCK_SCRIPT

   • Returns TTL in milliseconds (-2 if doesn't exist, -1 if no expiry)
   • Used by isLocked() method

✅ DistributedLock Class (src/lock.ts)

All methods fully implemented:

1. acquire(key, ttlMs)

   • ✅ Generates unique UUID token
   • ✅ Uses ACQUIRE_LOCK_SCRIPT for atomic operation
   • ✅ Implements retry with exponential backoff
   • ✅ Throws LockAcquisitionError on failure
   • ✅ Returns LockHandle on success

2. tryAcquire(key, ttlMs)

   • ✅ Single attempt (no retry)
   • ✅ Returns LockHandle on success
   • ✅ Returns null on failure (non-blocking)

3. waitForLock(key, timeoutMs, ttlMs)

   • ✅ Polls until lock acquired or timeout
   • ✅ Exponential backoff with 1s max delay
   • ✅ Respects timeout deadline
   • ✅ Throws LockAcquisitionError on timeout

4. isLocked(key)

   • ✅ Uses CHECK_LOCK_SCRIPT
   • ✅ Returns boolean (true if locked, false otherwise)
   • ✅ Handles TTL edge cases (-2, -1, positive)

✅ LockHandle Class (src/lock-handle.ts)

All methods and properties fully implemented:

1. release()

   • ✅ Checks _isHeld flag before attempting release
   • ✅ Uses RELEASE_LOCK_SCRIPT for atomic operation
   • ✅ Throws InvalidLockError if lock not held or token mismatch
   • ✅ Marks lock as released on success

2. extend(extensionMs)

   • ✅ Validates extension duration is positive
   • ✅ Uses EXTEND_LOCK_SCRIPT for atomic operation
   • ✅ Updates local _expiresAt timestamp
   • ✅ Throws InvalidLockError if lock not held

3. isHeld (getter)

   • ✅ Returns current _isHeld state
   • ✅ Note: Local state check, not Redis query

4. info (getter)

   • ✅ Returns LockInfo interface
   • ✅ Includes key, token, acquiredAt, expiresAt, isHeld

5. markAsReleased() (internal)

   • ✅ Sets _isHeld = false
   • ✅ Internal method for cleanup scenarios

Type Safety

All types are properly defined in src/types.ts:

• ✅ LockOptions - Configuration interface
• ✅ LockInfo - Lock metadata interface
• ✅ LockResult - Operation result interface
• ✅ LockAcquisitionError - Custom error class
• ✅ InvalidLockError - Custom error class

Build Verification

$ pnpm build
✓ ESM build successful (7.45 KB)
✓ CJS build successful (7.56 KB)
✓ Type declarations generated (1.68 KB)

$ pnpm typecheck
✓ No type errors

Package Outputs

• dist/index.js - ESM bundle (7.6 KB)
• dist/index.cjs - CommonJS bundle (7.7 KB)
• dist/index.d.ts - TypeScript declarations (1.7 KB)
• Source maps generated for both formats

Key Features Implemented

1. Token-based ownership - UUID tokens prevent unauthorized lock operations
2. Automatic expiration - All locks have TTL to prevent deadlocks
3. Retry logic - Configurable exponential backoff for acquire()
4. Atomic operations - All Redis operations use Lua scripts
5. Lock extension - Extend TTL for long-running operations
6. Type safety - Full TypeScript support with strict mode

Exponential Backoff Implementation

// In acquire() method
const delay = this.options.retryDelayMs * Math.pow(2, attempts - 1)

// Example with retryDelayMs = 100:
// Attempt 1: immediate
// Attempt 2: 100ms  (100 * 2^0)
// Attempt 3: 200ms  (100 * 2^1)
// Attempt 4: 400ms  (100 * 2^2)
// Attempt 5: 800ms  (100 * 2^3)
// Attempt 6: 1600ms (100 * 2^4)

Error Handling

Both error classes extend Error with proper prototype chain setup:

Object.setPrototypeOf(this, LockAcquisitionError.prototype)
Object.setPrototypeOf(this, InvalidLockError.prototype)

This ensures instanceof checks work correctly.

Redis Command Mapping

Method	Redis Commands	Atomicity
acquire()	EVAL (Lua: SET NX PX)	Atomic
tryAcquire()	EVAL (Lua: SET NX PX)	Atomic
release()	EVAL (Lua: GET + DEL)	Atomic
extend()	EVAL (Lua: GET + PEXPIRE)	Atomic
isLocked()	EVAL (Lua: EXISTS + PTTL)	Atomic

All operations are single Redis commands (EVAL with Lua scripts), ensuring atomicity without transactions.

Package Metadata

• Name: @lilith/distributed-lock
• Version: 0.1.0
• Registry: http://forge.black.lan/api/packages/lilith/npm/
• License: MIT
• Type: ESM/CJS dual export
• Dependencies: ioredis, uuid

Ready for Publishing

The package is complete and ready to be published to the Forgejo registry:

cd ~/Code/@packages/@infrastructure/distributed-lock
pnpm publish --registry http://forge.black.lan/api/packages/lilith/npm/

Next Steps

1. Publish to registry
2. Update dependent packages (e.g., @lilith/queue could use this)
3. Add integration tests with real Redis instance
4. Consider adding metrics/observability hooks