members.go

package alternator

import (
	"container/list"
	"fmt"
	"sync"
)

// Members stores the members of a node
type Members struct {
	sync.RWMutex
	List *list.List
	Map  map[Key]*list.Element
}

// Init initializes a Members struct. It must be called before any other call
// to a Members method.
func (members *Members) init() {
	members.List = list.New()
	members.Map = make(map[Key]*list.Element)
	// altNode.Members.Add(&selfExt)
}

// getPeer gets a peer from an element of Members.List
func getPeer(e *list.Element) *Peer {
	if e != nil {
		return e.Value.(*Peer)
	}
	return nil
}

// findSuccessor finds the successor of a key in the ring
func (members *Members) findSuccessor(key Key) *list.Element {
	// Find ID of successor
	for e := members.List.Front(); e != nil; e = e.Next() {
		if getPeer(e).ID.Compare(key) > 0 {
			return e
		}
	}
	// Nothing bigger in ring, successor is first node
	return members.List.Front()
}

// insert adds a node to the members if not already there, returns true if added
func (members *Members) insert(peer *Peer) *list.Element {
	i := 0
	// Iterate through members
	for e := members.List.Front(); e != nil; e = e.Next() {
		if e == nil {
			break
		}
		current := getPeer(e)
		var prevID Key
		if prev := e.Prev(); prev != nil {
			prevID = getPeer(prev).ID
		} else {
			prevID = MinKey
		}
		// Already in Members
		if peer.ID.Compare(current.ID) == 0 {
			return nil
		} else if (peer.ID.Compare(prevID) > 0) && (peer.ID.Compare(current.ID) < 0) {
			// Correct spot to add, add to list and map
			e := members.List.InsertBefore(peer, e)
			members.Map[peer.ID] = e
			return e
		}
		i++
	}
	// Append at end if not in members and not added by loop
	e := members.List.PushBack(peer)
	members.Map[peer.ID] = e
	return e
}

// remove deletes a node from members
func (members *Members) remove(del *Peer) {
	for e := members.List.Front(); e != nil; e = e.Next() {
		if getPeer(e).ID == del.ID {
			members.List.Remove(e)
			delete(members.Map, del.ID)
		}
	}
}

func (members Members) String() (str string) {
	i := 0
	for e := members.List.Front(); e != nil; e = e.Next() {
		str += fmt.Sprintf("member %d: %s\n", i, getPeer(e).String())
		i++
	}
	return
}

// getRandom returns a random member from the ring
func (members *Members) getRandom() *Peer {
	// i := 0
	// random := rand.Intn(len(members.Map))
	// for _, member := range members.Map {
	// 	if i == random {
	// 		return getPeer(member)
	// 	}
	// 	i++
	// }
	for _, member := range members.Map {
		return getPeer(member)
	}
	return nil
}