feat: init project with distributed lock implementation

- Add DistributedLock with Acquire/Release/Refresh using Lua scripts
- Add AcquireWithRetry with configurable retry interval and max retries
- Add integration tests for all lock operations
- Add .env for Redis connection (gitignored)

lock/lock.go

@@ -0,0 +1,113 @@
+package lock
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"github.com/redis/go-redis/v9"
+)
+
+var (
+	ErrLockNotAcquired = errors.New("lock not acquired")
+	ErrLockNotHeld     = errors.New("lock not held by this owner")
+)
+
+// DistributedLock 基于 Redis 的分布式锁
+type DistributedLock struct {
+	client   *redis.Client
+	key      string
+	owner    string // 唯一标识，用于安全释放锁
+	ttl      time.Duration
+}
+
+// New 创建一个分布式锁实例
+//   - client: Redis 客户端
+//   - key: 锁的 key
+//   - owner: 持有者唯一标识（如 UUID）
+//   - ttl: 锁的过期时间，防止死锁
+func New(client *redis.Client, key string, owner string, ttl time.Duration) *DistributedLock {
+	return &DistributedLock{
+		client: client,
+		key:    key,
+		owner:  owner,
+		ttl:    ttl,
+	}
+}
+
+// Acquire 尝试获取锁（非阻塞）
+func (l *DistributedLock) Acquire(ctx context.Context) (bool, error) {
+	ok, err := l.client.SetNX(ctx, l.key, l.owner, l.ttl).Result()
+	if err != nil {
+		return false, err
+	}
+	return ok, nil
+}
+
+// AcquireWithRetry 带重试的获取锁
+//   - retryInterval: 重试间隔
+//   - maxRetries: 最大重试次数，0 表示无限重试
+func (l *DistributedLock) AcquireWithRetry(ctx context.Context, retryInterval time.Duration, maxRetries int) (bool, error) {
+	for i := 0; maxRetries == 0 || i < maxRetries; i++ {
+		acquired, err := l.Acquire(ctx)
+		if err != nil {
+			return false, err
+		}
+		if acquired {
+			return true, nil
+		}
+
+		select {
+		case <-ctx.Done():
+			return false, ctx.Err()
+		case <-time.After(retryInterval):
+		}
+	}
+	return false, ErrLockNotAcquired
+}
+
+// Release 释放锁（仅当自己持有时才释放，使用 Lua 脚本保证原子性）
+func (l *DistributedLock) Release(ctx context.Context) error {
+	script := redis.NewScript(`
+		if redis.call("GET", KEYS[1]) == ARGV[1] then
+			return redis.call("DEL", KEYS[1])
+		else
+			return 0
+		end
+	`)
+
+	result, err := script.Run(ctx, l.client, []string{l.key}, l.owner).Int64()
+	if err != nil {
+		return err
+	}
+	if result == 0 {
+		return ErrLockNotHeld
+	}
+	return nil
+}
+
+// Refresh 续期锁（延长 TTL，仅当自己持有时才续期）
+func (l *DistributedLock) Refresh(ctx context.Context) (bool, error) {
+	script := redis.NewScript(`
+		if redis.call("GET", KEYS[1]) == ARGV[1] then
+			return redis.call("PEXPIRE", KEYS[1], ARGV[2])
+		else
+			return 0
+		end
+	`)
+
+	result, err := script.Run(ctx, l.client, []string{l.key}, l.owner, l.ttl.Milliseconds()).Int64()
+	if err != nil {
+		return false, err
+	}
+	return result == 1, nil
+}
+
+// IsHeld 检查锁是否被持有（不一定是自己）
+func (l *DistributedLock) IsHeld(ctx context.Context) (bool, error) {
+	val, err := l.client.Exists(ctx, l.key).Result()
+	if err != nil {
+		return false, err
+	}
+	return val > 0, nil
+}