Function cmdRPOPLPUSH

lists.go:197–293

(m uhaha.Machine, args []string)

}

func cmdRPOPLPUSH(m uhaha.Machine, args []string) (interface{}, error) {

	if len(args) != 3 {
		return nil, uhaha.ErrWrongNumArgs
	}
	source, dest := []byte(args[1]), []byte(args[2])

	var ttl int64 = -1
	var expireTime int64 = -1
	if bytes.Compare(source, dest) == 0 {
		var err error
		ttl, err = ldb.LTTL(source)
		if err != nil {
			return nil, err
		}
		if ttl != -1 {
			expireTime = m.Now().Unix() + ttl
		}
	}

	// Special handling for same source and destination (rotation)
	if bytes.Compare(source, dest) == 0 {
		// Use global mutex for same source/destination operations
		// to ensure absolute atomicity
		sameKeyMutex.Lock()
		defer sameKeyMutex.Unlock()

		// Get the last element
		data, err := ldb.RPop(source)
		if err != nil {
			return nil, err
		}

		if data == nil {
			return nil, nil
		}

		// Push it back to the front
		if _, err := ldb.LPush(source, data); err != nil {
			// If push fails, revert the pop
			ldb.RPush(source, data)
			return nil, err
		}

		//reset ttl using absolute time
		if expireTime != -1 {
			ldb.LExpireAt(source, expireTime)
		}

		return data, nil
	}

	// For different source and destination, we need to lock both keys
	// to prevent deadlocks, we always lock in a consistent order
	var firstKey, secondKey []byte
	if bytes.Compare(source, dest) < 0 {
		firstKey = source
		secondKey = dest