micro/selector/cache/cache.go

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package cache
import (
"sync"
"time"
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"github.com/micro/go-log"
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"github.com/micro/go-micro/registry"
"github.com/micro/go-micro/selector"
)
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/*
Cache selector is a selector which uses the registry.Watcher to Cache service entries.
It defaults to a TTL for 1 minute and causes a cache miss on the next request.
*/
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type cacheSelector struct {
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so selector.Options
ttl time.Duration
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// registry cache
sync.Mutex
cache map[string][]*registry.Service
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ttls map[string]time.Time
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once sync.Once
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// used to close or reload watcher
reload chan bool
exit chan bool
}
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var (
DefaultTTL = time.Minute
)
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func (c *cacheSelector) quit() bool {
select {
case <-c.exit:
return true
default:
return false
}
}
// cp copies a service. Because we're caching handing back pointers would
// create a race condition, so we do this instead
// its fast enough
func (c *cacheSelector) cp(current []*registry.Service) []*registry.Service {
var services []*registry.Service
for _, service := range current {
// copy service
s := new(registry.Service)
*s = *service
// copy nodes
var nodes []*registry.Node
for _, node := range service.Nodes {
n := new(registry.Node)
*n = *node
nodes = append(nodes, n)
}
s.Nodes = nodes
// copy endpoints
var eps []*registry.Endpoint
for _, ep := range service.Endpoints {
e := new(registry.Endpoint)
*e = *ep
eps = append(eps, e)
}
s.Endpoints = eps
// append service
services = append(services, s)
}
return services
}
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func (c *cacheSelector) del(service string) {
delete(c.cache, service)
delete(c.ttls, service)
}
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func (c *cacheSelector) get(service string) ([]*registry.Service, error) {
c.Lock()
defer c.Unlock()
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// get does the actual request for a service
// it also caches it
get := func(service string) ([]*registry.Service, error) {
// ask the registry
services, err := c.so.Registry.GetService(service)
if err != nil {
return nil, err
}
// cache results
c.set(service, c.cp(services))
return services, nil
}
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// check the cache first
services, ok := c.cache[service]
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// cache miss or no services
if !ok || len(services) == 0 {
return get(service)
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}
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// got cache but lets check ttl
ttl, kk := c.ttls[service]
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// within ttl so return cache
if kk && time.Since(ttl) < c.ttl {
return c.cp(services), nil
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}
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// expired entry so get service
if services, err := get(service); err == nil {
return services, nil
}
// return expired cache as last resort
return c.cp(services), nil
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}
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func (c *cacheSelector) set(service string, services []*registry.Service) {
c.cache[service] = services
c.ttls[service] = time.Now().Add(c.ttl)
}
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func (c *cacheSelector) 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":
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c.del(res.Service.Name)
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}
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 {
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c.set(res.Service.Name, append(services, res.Service))
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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
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c.set(res.Service.Name, services)
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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)
}
}
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// 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)
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return
}
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// 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)
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}
}
// run starts the cache watcher loop
// it creates a new watcher if there's a problem
// reloads the watcher if Init is called
// and returns when Close is called
func (c *cacheSelector) run() {
for {
// exit early if already dead
if c.quit() {
return
}
// create new watcher
w, err := c.so.Registry.Watch()
if err != nil {
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if c.quit() {
return
}
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log.Log(err)
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time.Sleep(time.Second)
continue
}
// watch for events
if err := c.watch(w); err != nil {
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if c.quit() {
return
}
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log.Log(err)
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continue
}
}
}
// watch loops the next event and calls update
// it returns if there's an error
func (c *cacheSelector) watch(w registry.Watcher) error {
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defer w.Stop()
// manage this loop
go func() {
// wait for exit or reload signal
select {
case <-c.exit:
case <-c.reload:
}
// stop the watcher
w.Stop()
}()
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for {
res, err := w.Next()
if err != nil {
return err
}
c.update(res)
}
}
func (c *cacheSelector) Init(opts ...selector.Option) error {
for _, o := range opts {
o(&c.so)
}
// reload the watcher
go func() {
select {
case <-c.exit:
return
default:
c.reload <- true
}
}()
return nil
}
func (c *cacheSelector) Options() selector.Options {
return c.so
}
func (c *cacheSelector) Select(service string, opts ...selector.SelectOption) (selector.Next, error) {
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c.once.Do(func() {
go c.run()
})
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sopts := selector.SelectOptions{
Strategy: c.so.Strategy,
}
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for _, opt := range opts {
opt(&sopts)
}
// get the service
// try the cache first
// if that fails go directly to the registry
services, err := c.get(service)
if err != nil {
return nil, err
}
// apply the filters
for _, filter := range sopts.Filters {
services = filter(services)
}
// if there's nothing left, return
if len(services) == 0 {
return nil, selector.ErrNoneAvailable
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}
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return sopts.Strategy(services), nil
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}
func (c *cacheSelector) Mark(service string, node *registry.Node, err error) {
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return
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}
func (c *cacheSelector) Reset(service string) {
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return
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}
// Close stops the watcher and destroys the cache
func (c *cacheSelector) Close() error {
c.Lock()
c.cache = make(map[string][]*registry.Service)
c.Unlock()
select {
case <-c.exit:
return nil
default:
close(c.exit)
}
return nil
}
func (c *cacheSelector) String() string {
return "cache"
}
func NewSelector(opts ...selector.Option) selector.Selector {
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sopts := selector.Options{
Strategy: selector.Random,
}
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for _, opt := range opts {
opt(&sopts)
}
if sopts.Registry == nil {
sopts.Registry = registry.DefaultRegistry
}
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ttl := DefaultTTL
if sopts.Context != nil {
if t, ok := sopts.Context.Value(ttlKey{}).(time.Duration); ok {
ttl = t
}
}
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return &cacheSelector{
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so: sopts,
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ttl: ttl,
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cache: make(map[string][]*registry.Service),
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ttls: make(map[string]time.Time),
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reload: make(chan bool, 1),
exit: make(chan bool),
}
}