dsync.go

/*
 * Minio Cloud Storage, (C) 2016 Minio, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package dsync

import (
	"errors"
)

// Dsync represents dsync client object which is initialized with
// authenticated clients, used to initiate lock RPC calls.
type Dsync struct {
	// Number of nodes participating in the distributed locking.
	dNodeCount int

	// List of rpc client objects, one per lock server.
	rpcClnts []NetLocker

	// Index into rpc client array for server running on localhost
	ownNode int

	// Simple majority based quorum, set to dNodeCount/2+1
	dquorum int

	// Simple quorum for read operations, set to dNodeCount/2
	dquorumReads int
}

// New - initializes a new dsync object with input rpcClnts.
func New(rpcClnts []NetLocker, rpcOwnNode int) (*Dsync, error) {
	if len(rpcClnts) < 4 {
		return nil, errors.New("Dsync is not designed for less than 4 nodes")
	} else if len(rpcClnts) > 16 {
		return nil, errors.New("Dsync is not designed for more than 16 nodes")
	} else if len(rpcClnts)%2 != 0 {
		return nil, errors.New("Dsync is not designed for an uneven number of nodes")
	}

	if rpcOwnNode > len(rpcClnts) {
		return nil, errors.New("Index for own node is too large")
	}

	ds := &Dsync{}
	ds.dNodeCount = len(rpcClnts)
	ds.dquorum = ds.dNodeCount/2 + 1
	ds.dquorumReads = ds.dNodeCount / 2
	ds.ownNode = rpcOwnNode

	// Initialize node name and rpc path for each NetLocker object.
	ds.rpcClnts = make([]NetLocker, ds.dNodeCount)
	copy(ds.rpcClnts, rpcClnts)

	return ds, nil
}