go-cart-actor/synced-pool.go

package main

import (
	"fmt"
	"log"
	"strings"
	"sync"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
	"k8s.io/apimachinery/pkg/watch"
)

type Quorum interface {
	Negotiate(knownHosts []string) ([]string, error)
	OwnerChanged(CartId, host string) error
}

type HealthHandler interface {
	IsHealthy() bool
}

type SyncedPool struct {
	*Server
	mu          sync.RWMutex
	Hostname    string
	local       *GrainLocalPool
	remotes     map[string]*RemoteHost
	remoteIndex map[CartId]*RemoteGrain
}

var (
	negotiationCount = promauto.NewCounter(prometheus.CounterOpts{
		Name: "cart_remote_negotiation_total",
		Help: "The total number of remote negotiations",
	})
	grainSyncCount = promauto.NewCounter(prometheus.CounterOpts{
		Name: "cart_grain_sync_total",
		Help: "The total number of grain owner changes",
	})
	connectedRemotes = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "cart_connected_remotes",
		Help: "The number of connected remotes",
	})
	remoteLookupCount = promauto.NewCounter(prometheus.CounterOpts{
		Name: "cart_remote_lookup_total",
		Help: "The total number of remote lookups",
	})
	packetQueue = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "cart_packet_queue_size",
		Help: "The total number of packets in the queue",
	})
	packetsSent = promauto.NewCounter(prometheus.CounterOpts{
		Name: "cart_pool_packets_sent_total",
		Help: "The total number of packets sent",
	})
	packetsReceived = promauto.NewCounter(prometheus.CounterOpts{
		Name: "cart_pool_packets_received_total",
		Help: "The total number of packets received",
	})
)

func (p *SyncedPool) PongHandler(data []byte) (PoolMessage, []byte, error) {
	return Pong, data, nil
}

func (p *SyncedPool) GetCartIdHandler(data []byte) (PoolMessage, []byte, error) {
	ids := make([]string, 0, len(p.local.grains))
	for id := range p.local.grains {
		if p.local.grains[id] == nil {
			continue
		}
		s := id.String()
		if s == "" {
			continue
		}
		ids = append(ids, s)
	}
	log.Printf("Returning %d cart ids\n", len(ids))
	return CartIdsResponse, []byte(strings.Join(ids, ";")), nil
}

func (p *SyncedPool) NegotiateHandler(data []byte) (PoolMessage, []byte, error) {
	negotiationCount.Inc()
	log.Printf("Handling negotiation\n")
	for _, host := range p.ExcludeKnown(strings.Split(string(data), ";")) {
		if host == "" {
			continue
		}
		go p.AddRemote(host)

	}

	return RemoteNegotiateResponse, []byte("ok"), nil
}

func (p *SyncedPool) GrainOwnerChangeHandler(data []byte) (PoolMessage, []byte, error) {
	grainSyncCount.Inc()

	idAndHostParts := strings.Split(string(data), ";")
	if len(idAndHostParts) != 2 {
		log.Printf("Invalid remote grain change message\n")
		return AckChange, []byte("incorrect"), fmt.Errorf("invalid remote grain change message")
	}
	id := ToCartId(idAndHostParts[0])
	host := idAndHostParts[1]
	log.Printf("Handling remote grain owner change to %s for id %s\n", host, id)
	for _, r := range p.remotes {
		if r.Host == host {
			// log.Printf("Remote grain %s changed to %s\n", id, host)

			go p.SpawnRemoteGrain(id, host)

			return AckChange, []byte("ok"), nil
		}
	}
	go p.AddRemote(host)
	return AckChange, []byte("ok"), nil
}

func (p *SyncedPool) RemoveRemoteGrain(id CartId) {
	p.mu.Lock()
	defer p.mu.Unlock()
	delete(p.remoteIndex, id)
}

func (p *SyncedPool) SpawnRemoteGrain(id CartId, host string) {
	if id.String() == "" {
		log.Printf("Invalid grain id, %s\n", id)
		return
	}
	if p.local.grains[id] != nil {
		log.Printf("Grain %s already exists locally, owner is (%s)\n", id, host)
		p.mu.Lock()
		delete(p.local.grains, id)
		p.mu.Unlock()
	}

	remote, err := NewRemoteGrain(id, host)
	if err != nil {
		log.Printf("Error creating remote grain %v\n", err)
		return
	}
	go func() {
		<-remote.PersistentConnection.Died
		p.RemoveRemoteGrain(id)
		p.HandleHostError(host)
		log.Printf("Remote grain %s died, host: %s\n", id.String(), host)
	}()

	p.mu.Lock()
	p.remoteIndex[id] = remote
	p.mu.Unlock()
}

func (p *SyncedPool) HandleHostError(host string) {
	for _, r := range p.remotes {
		if r.Host == host {
			if !r.IsHealthy() {
				p.RemoveHost(r)
			} else {
				r.ErrorCount++
			}
			return
		}
	}
}

func NewSyncedPool(local *GrainLocalPool, hostname string, discovery Discovery) (*SyncedPool, error) {
	listen := fmt.Sprintf("%s:1338", hostname)

	server, err := Listen(listen)
	if err != nil {
		return nil, err
	}

	log.Printf("Listening on %s", listen)

	pool := &SyncedPool{
		Server:   server,
		Hostname: hostname,
		local:    local,

		remotes:     make(map[string]*RemoteHost),
		remoteIndex: make(map[CartId]*RemoteGrain),
	}

	server.HandleCall(Ping, pool.PongHandler)
	server.HandleCall(GetCartIds, pool.GetCartIdHandler)
	server.HandleCall(RemoteNegotiate, pool.NegotiateHandler)
	server.HandleCall(RemoteGrainChanged, pool.GrainOwnerChangeHandler)

	if discovery != nil {
		go func() {
			time.Sleep(time.Second * 5)
			log.Printf("Starting discovery")
			ch, err := discovery.Watch()
			if err != nil {
				log.Printf("Error discovering hosts: %v", err)
				return
			}
			for chng := range ch {
				if chng.Host == "" {
					continue
				}
				known := pool.IsKnown(chng.Host)
				if chng.Type != watch.Deleted && !known {
					go func(h string) {
						log.Printf("Discovered host %s, waiting for startup", h)
						time.Sleep(time.Second)
						pool.AddRemote(h)
					}(chng.Host)
				} else if chng.Type == watch.Deleted && known {
					log.Printf("Host removed %s, removing from index", chng.Host)
					for _, r := range pool.remotes {
						if r.Host == chng.Host {
							pool.RemoveHost(r)
							break
						}
					}
				}
			}
		}()
	} else {
		log.Printf("No discovery, waiting for remotes to connect")
	}

	return pool, nil
}

func (p *SyncedPool) IsHealthy() bool {
	for _, r := range p.remotes {
		if !r.IsHealthy() {
			return false
		}
	}
	return true
}

func (p *SyncedPool) IsKnown(host string) bool {
	for _, r := range p.remotes {
		if r.Host == host {
			return true
		}
	}

	return host == p.Hostname
}

func (p *SyncedPool) ExcludeKnown(hosts []string) []string {
	ret := make([]string, 0, len(hosts))
	for _, h := range hosts {
		if !p.IsKnown(h) {
			ret = append(ret, h)
		}
	}
	return ret
}

func (p *SyncedPool) RemoveHost(host *RemoteHost) {
	if p.remotes[host.Host] == nil {
		return
	}
	p.mu.Lock()
	defer p.mu.Unlock()

	h := p.remotes[host.Host]
	h.Close()
	delete(p.remotes, host.Host)

	connectedRemotes.Set(float64(len(p.remotes)))
}

func (p *SyncedPool) RemoveHostMappedCarts(host *RemoteHost) {
	p.mu.Lock()
	defer p.mu.Unlock()
	for id, r := range p.remoteIndex {
		if r.Host == host.Host {
			p.remoteIndex[id].Close()
			delete(p.remoteIndex, id)
		}
	}
}

type PoolMessage uint32

const (
	RemoteNegotiate    = PoolMessage(3)
	RemoteGrainChanged = PoolMessage(4)
	AckChange          = PoolMessage(5)
	//AckError           = PoolMessage(6)
	Ping                    = PoolMessage(7)
	Pong                    = PoolMessage(8)
	GetCartIds              = PoolMessage(9)
	CartIdsResponse         = PoolMessage(10)
	RemoteNegotiateResponse = PoolMessage(11)
)

func (p *SyncedPool) Negotiate() {
	knownHosts := make([]string, 0, len(p.remotes)+1)
	for _, r := range p.remotes {
		knownHosts = append(knownHosts, r.Host)
	}
	knownHosts = append([]string{p.Hostname}, knownHosts...)

	for _, r := range p.remotes {
		hosts, err := r.Negotiate(knownHosts)
		if err != nil {
			log.Printf("Error negotiating with %s: %v\n", r.Host, err)
			return
		}
		for _, h := range hosts {
			if !p.IsKnown(h) {
				p.AddRemote(h)
			}
		}
	}

}

func (p *SyncedPool) RequestOwnership(id CartId) error {
	ok := 0
	all := 0
	p.mu.RLock()
	for _, r := range p.remotes {
		log.Printf("Asking for confirmation change of %s to %s (me) with %s\n", id, p.Hostname, r.Host)
		err := r.ConfirmChange(id, p.Hostname)
		all++
		if err != nil {
			if !r.IsHealthy() {
				p.RemoveHost(r)
				all--
			} else {
				log.Printf("Error confirming change: %v from %s\n", err, p.Hostname)
			}
			continue
		}
		ok++
	}
	p.mu.RUnlock()
	if ok == 0 && all > 0 {
		p.removeLocalGrain(id)
		return fmt.Errorf("no remotes confirmed change")
	}
	if (all < 3 && ok < all) || ok < (all/2) {
		p.removeLocalGrain(id)
		return fmt.Errorf("quorum not reached")
	}
	return nil
}

func (p *SyncedPool) removeLocalGrain(id CartId) {
	p.mu.Lock()
	defer p.mu.Unlock()
	delete(p.local.grains, id)
}

func (p *SyncedPool) AddRemote(host string) error {
	p.mu.Lock()
	defer p.mu.Unlock()
	_, hasHost := p.remotes[host]
	if host == "" || p.IsKnown(host) || hasHost {
		return nil
	}
	client, err := Dial(fmt.Sprintf("%s:1338", host))
	if err != nil {
		log.Printf("Error connecting to remote %s: %v\n", host, err)
		return err
	}

	remote := RemoteHost{
		Client:      client,
		MissedPings: 0,
		Host:        host,
	}
	p.remotes[host] = &remote
	go func() {
		<-remote.PersistentConnection.Died
		log.Printf("Removing host, remote died %s", host)
		p.RemoveHost(&remote)
	}()
	go func() {
		for range time.Tick(time.Second * 3) {
			err := remote.Ping()

			for err != nil {
				time.Sleep(time.Millisecond * 200)
				if !remote.IsHealthy() {
					log.Printf("Removing host, unable to communicate with %s", host)
					p.RemoveHost(&remote)
					return
				}
				err = remote.Ping()
			}
		}
	}()

	connectedRemotes.Set(float64(len(p.remotes)))
	log.Printf("Added remote %s\n", remote.Host)

	go remote.Initialize(p)
	return nil
}

func (p *SyncedPool) getGrain(id CartId) (Grain, error) {
	localGrain, ok := p.local.grains[id]
	if !ok {
		// check if remote grain exists
		p.mu.RLock()
		remoteGrain, ok := p.remoteIndex[id]
		p.mu.RUnlock()
		if ok {
			remoteLookupCount.Inc()
			return remoteGrain, nil
		}

		err := p.RequestOwnership(id)
		if err != nil {
			log.Printf("Error requesting ownership: %v\n", err)
			return nil, err
		}

		localGrain, err = p.local.GetGrain(id)
		if err != nil {
			return nil, err
		}

	}
	return localGrain, nil
}

func (p *SyncedPool) Process(id CartId, messages ...Message) (*CallResult, error) {
	pool, err := p.getGrain(id)
	var res *CallResult
	if err != nil {
		return nil, err
	}
	for _, m := range messages {
		res, err = pool.HandleMessage(&m, false)
		if err != nil {
			return nil, err
		}
	}
	return res, nil
}

func (p *SyncedPool) Get(id CartId) (*CallResult, error) {
	grain, err := p.getGrain(id)
	if err != nil {
		return nil, err
	}

	return grain.GetCurrentState()
}