strategy.go

// MIT License
//
// Copyright (c) 2020 Lack
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package selector

import (
	"math/rand"
	"sync"
	"time"

	regpb "github.com/vine-io/vine/proto/apis/registry"
)

func init() {
	rand.Seed(time.Now().UnixNano())
}

// Random is a random strategy algorithm for node selection
func Random(services []*regpb.Service) Next {
	nodes := make([]*regpb.Node, 0, len(services))

	for _, service := range services {
		nodes = append(nodes, service.Nodes...)
	}

	return func() (*regpb.Node, error) {
		if len(nodes) == 0 {
			return nil, ErrNoneAvailable
		}

		i := rand.Int() % len(nodes)
		return nodes[i], nil
	}
}

// RoundRobin is a roundrobin strategy algorithm for node selection
func RoundRobin(services []*regpb.Service) Next {
	nodes := make([]*regpb.Node, 0, len(services))

	for _, service := range services {
		nodes = append(nodes, service.Nodes...)
	}

	var i = rand.Int()
	var mtx sync.Mutex

	return func() (*regpb.Node, error) {
		if len(nodes) == 0 {
			return nil, ErrNoneAvailable
		}

		mtx.Lock()
		node := nodes[i%len(nodes)]
		i++
		mtx.Unlock()

		return node, nil
	}
}