micro/registry/cache/cache.go

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// Package cache provides a registry cache
package cache
import (
"math"
"math/rand"
"sync"
"time"
"github.com/micro/go-micro/registry"
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log "github.com/micro/go-micro/util/log"
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)
// Cache is the registry cache interface
type Cache interface {
// embed the registry interface
registry.Registry
// stop the cache watcher
Stop()
}
type Options struct {
// TTL is the cache TTL
TTL time.Duration
}
type Option func(o *Options)
type cache struct {
registry.Registry
opts Options
// registry cache
sync.RWMutex
cache map[string][]*registry.Service
ttls map[string]time.Time
watched map[string]bool
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// used to stop the cache
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exit chan bool
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// status of the registry
// used to hold onto the cache
// in failure state
status error
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}
var (
DefaultTTL = time.Minute
)
func backoff(attempts int) time.Duration {
if attempts == 0 {
return time.Duration(0)
}
return time.Duration(math.Pow(10, float64(attempts))) * time.Millisecond
}
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func (c *cache) getStatus() error {
c.RLock()
defer c.RUnlock()
return c.status
}
func (c *cache) setStatus(err error) {
c.Lock()
c.status = err
c.Unlock()
}
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// isValid checks if the service is valid
func (c *cache) isValid(services []*registry.Service, ttl time.Time) bool {
// no services exist
if len(services) == 0 {
return false
}
// ttl is invalid
if ttl.IsZero() {
return false
}
// time since ttl is longer than timeout
if time.Since(ttl) > c.opts.TTL {
return false
}
// ok
return true
}
func (c *cache) quit() bool {
select {
case <-c.exit:
return true
default:
return false
}
}
func (c *cache) del(service string) {
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// don't blow away cache in error state
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if err := c.status; err != nil {
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return
}
// otherwise delete entries
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delete(c.cache, service)
delete(c.ttls, service)
}
func (c *cache) get(service string) ([]*registry.Service, error) {
// read lock
c.RLock()
// check the cache first
services := c.cache[service]
// get cache ttl
ttl := c.ttls[service]
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// make a copy
cp := registry.Copy(services)
// unlock the read lock
c.RUnlock()
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// got services && within ttl so return cache
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if c.isValid(cp, ttl) {
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// return servics
return cp, nil
}
// get does the actual request for a service and cache it
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get := func(service string, cached []*registry.Service) ([]*registry.Service, error) {
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// ask the registry
services, err := c.Registry.GetService(service)
if err != nil {
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// check the cache
if len(cached) > 0 {
// set the error status
c.setStatus(err)
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// return the stale cache
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return cached, nil
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}
// otherwise return error
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return nil, err
}
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// reset the status
if c.getStatus(); err != nil {
c.setStatus(nil)
}
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// cache results
c.Lock()
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c.set(service, registry.Copy(services))
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c.Unlock()
return services, nil
}
// watch service if not watched
if _, ok := c.watched[service]; !ok {
go c.run(service)
}
// get and return services
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return get(service, services)
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}
func (c *cache) set(service string, services []*registry.Service) {
c.cache[service] = services
c.ttls[service] = time.Now().Add(c.opts.TTL)
}
func (c *cache) update(res *registry.Result) {
if res == nil || res.Service == nil {
return
}
c.Lock()
defer c.Unlock()
services, ok := c.cache[res.Service.Name]
if !ok {
// we're not going to cache anything
// unless there was already a lookup
return
}
if len(res.Service.Nodes) == 0 {
switch res.Action {
case "delete":
c.del(res.Service.Name)
}
return
}
// existing service found
var service *registry.Service
var index int
for i, s := range services {
if s.Version == res.Service.Version {
service = s
index = i
}
}
switch res.Action {
case "create", "update":
if service == nil {
c.set(res.Service.Name, append(services, res.Service))
return
}
// append old nodes to new service
for _, cur := range service.Nodes {
var seen bool
for _, node := range res.Service.Nodes {
if cur.Id == node.Id {
seen = true
break
}
}
if !seen {
res.Service.Nodes = append(res.Service.Nodes, cur)
}
}
services[index] = res.Service
c.set(res.Service.Name, services)
case "delete":
if service == nil {
return
}
var nodes []*registry.Node
// filter cur nodes to remove the dead one
for _, cur := range service.Nodes {
var seen bool
for _, del := range res.Service.Nodes {
if del.Id == cur.Id {
seen = true
break
}
}
if !seen {
nodes = append(nodes, cur)
}
}
// still got nodes, save and return
if len(nodes) > 0 {
service.Nodes = nodes
services[index] = service
c.set(service.Name, services)
return
}
// zero nodes left
// only have one thing to delete
// nuke the thing
if len(services) == 1 {
c.del(service.Name)
return
}
// still have more than 1 service
// check the version and keep what we know
var srvs []*registry.Service
for _, s := range services {
if s.Version != service.Version {
srvs = append(srvs, s)
}
}
// save
c.set(service.Name, srvs)
}
}
// run starts the cache watcher loop
// it creates a new watcher if there's a problem
func (c *cache) run(service string) {
// set watcher
c.Lock()
c.watched[service] = true
c.Unlock()
// delete watcher on exit
defer func() {
c.Lock()
delete(c.watched, service)
c.Unlock()
}()
var a, b int
for {
// exit early if already dead
if c.quit() {
return
}
// jitter before starting
j := rand.Int63n(100)
time.Sleep(time.Duration(j) * time.Millisecond)
// create new watcher
w, err := c.Registry.Watch(
registry.WatchService(service),
)
if err != nil {
if c.quit() {
return
}
d := backoff(a)
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c.setStatus(err)
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if a > 3 {
log.Log("rcache: ", err, " backing off ", d)
a = 0
}
time.Sleep(d)
a++
continue
}
// reset a
a = 0
// watch for events
if err := c.watch(w); err != nil {
if c.quit() {
return
}
d := backoff(b)
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c.setStatus(err)
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if b > 3 {
log.Log("rcache: ", err, " backing off ", d)
b = 0
}
time.Sleep(d)
b++
continue
}
// reset b
b = 0
}
}
// watch loops the next event and calls update
// it returns if there's an error
func (c *cache) watch(w registry.Watcher) error {
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// used to stop the watch
stop := make(chan bool)
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// manage this loop
go func() {
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defer w.Stop()
select {
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// wait for exit
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case <-c.exit:
return
// we've been stopped
case <-stop:
return
}
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}()
for {
res, err := w.Next()
if err != nil {
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close(stop)
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return err
}
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// reset the error status since we succeeded
if err := c.getStatus(); err != nil {
// reset status
c.setStatus(nil)
}
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c.update(res)
}
}
func (c *cache) GetService(service string) ([]*registry.Service, error) {
// get the service
services, err := c.get(service)
if err != nil {
return nil, err
}
// if there's nothing return err
if len(services) == 0 {
return nil, registry.ErrNotFound
}
// return services
return services, nil
}
func (c *cache) Stop() {
select {
case <-c.exit:
return
default:
close(c.exit)
}
}
func (c *cache) String() string {
return "rcache"
}
// New returns a new cache
func New(r registry.Registry, opts ...Option) Cache {
rand.Seed(time.Now().UnixNano())
options := Options{
TTL: DefaultTTL,
}
for _, o := range opts {
o(&options)
}
return &cache{
Registry: r,
opts: options,
watched: make(map[string]bool),
cache: make(map[string][]*registry.Service),
ttls: make(map[string]time.Time),
exit: make(chan bool),
}
}