syncthing/lib/discover/cache.go

199 lines
5.1 KiB
Go
Raw Normal View History

2015-09-21 08:34:20 +00:00
// Copyright (C) 2015 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at http://mozilla.org/MPL/2.0/.
package discover
import (
stdsync "sync"
"time"
"github.com/syncthing/protocol"
"github.com/syncthing/syncthing/lib/sync"
"github.com/thejerf/suture"
)
// The CachingMux aggregates results from multiple Finders. Each Finder has
// an associated cache time and negative cache time. The cache time sets how
// long we cache and return successfull lookup results, the negative cache
// time sets how long we refrain from asking about the same device ID after
// receiving a negative answer. The value of zero disables caching (positive
// or negative).
type CachingMux struct {
*suture.Supervisor
finders []cachedFinder
caches []*cache
mut sync.Mutex
}
// A cachedFinder is a Finder with associated cache timeouts.
type cachedFinder struct {
Finder
cacheTime time.Duration
negCacheTime time.Duration
}
func NewCachingMux() *CachingMux {
return &CachingMux{
Supervisor: suture.NewSimple("discover.cachingMux"),
mut: sync.NewMutex(),
}
}
// Add registers a new Finder, with associated cache timeouts.
func (m *CachingMux) Add(finder Finder, cacheTime, negCacheTime time.Duration) {
m.mut.Lock()
m.finders = append(m.finders, cachedFinder{finder, cacheTime, negCacheTime})
m.caches = append(m.caches, newCache())
m.mut.Unlock()
if svc, ok := finder.(suture.Service); ok {
m.Supervisor.Add(svc)
}
}
// Lookup attempts to resolve the device ID using any of the added Finders,
// while obeying the cache settings.
func (m *CachingMux) Lookup(deviceID protocol.DeviceID) (direct []string, relays []Relay, err error) {
m.mut.Lock()
for i, finder := range m.finders {
if cacheEntry, ok := m.caches[i].Get(deviceID); ok {
// We have a cache entry. Lets see what it says.
if cacheEntry.found && time.Since(cacheEntry.when) < finder.cacheTime {
// It's a positive, valid entry. Use it.
if debug {
l.Debugln("cached discovery entry for", deviceID, "at", finder.String())
l.Debugln(" ", cacheEntry)
}
direct = append(direct, cacheEntry.Direct...)
relays = append(relays, cacheEntry.Relays...)
continue
}
if !cacheEntry.found && time.Since(cacheEntry.when) < finder.negCacheTime {
// It's a negative, valid entry. We should not make another
// attempt right now.
if debug {
l.Debugln("negative cache entry for", deviceID, "at", finder.String())
}
continue
}
// It's expired. Ignore and continue.
}
// Perform the actual lookup and cache the result.
if td, tr, err := finder.Lookup(deviceID); err == nil {
if debug {
l.Debugln("lookup for", deviceID, "at", finder.String())
l.Debugln(" ", td)
l.Debugln(" ", tr)
}
direct = append(direct, td...)
relays = append(relays, tr...)
m.caches[i].Set(deviceID, CacheEntry{
Direct: td,
Relays: tr,
when: time.Now(),
found: len(td)+len(tr) > 0,
})
}
}
m.mut.Unlock()
if debug {
l.Debugln("lookup results for", deviceID)
l.Debugln(" ", direct)
l.Debugln(" ", relays)
}
return direct, relays, nil
}
func (m *CachingMux) String() string {
return "discovery cache"
}
func (m *CachingMux) Error() error {
return nil
}
func (m *CachingMux) ChildErrors() map[string]error {
m.mut.Lock()
children := make(map[string]error, len(m.finders))
for _, f := range m.finders {
children[f.String()] = f.Error()
}
m.mut.Unlock()
return children
}
func (m *CachingMux) Cache() map[protocol.DeviceID]CacheEntry {
// Res will be the "total" cache, i.e. the union of our cache and all our
// children's caches.
res := make(map[protocol.DeviceID]CacheEntry)
m.mut.Lock()
for i := range m.finders {
// Each finder[i] has a corresponding cache at cache[i]. Go through it
// and populate the total, if it's newer than what's already in there.
// We skip any negative cache entries.
for k, v := range m.caches[i].Cache() {
if v.found && v.when.After(res[k].when) {
res[k] = v
}
}
// Then ask the finder itself for it's cache and do the same. If this
// finder is a global discovery client, it will have no cache. If it's
// a local discovery client, this will be it's current state.
for k, v := range m.finders[i].Cache() {
if v.found && v.when.After(res[k].when) {
res[k] = v
}
}
}
m.mut.Unlock()
return res
}
// A cache can be embedded wherever useful
type cache struct {
entries map[protocol.DeviceID]CacheEntry
mut stdsync.Mutex
}
func newCache() *cache {
return &cache{
entries: make(map[protocol.DeviceID]CacheEntry),
}
}
func (c *cache) Set(id protocol.DeviceID, ce CacheEntry) {
c.mut.Lock()
c.entries[id] = ce
c.mut.Unlock()
}
func (c *cache) Get(id protocol.DeviceID) (CacheEntry, bool) {
c.mut.Lock()
ce, ok := c.entries[id]
c.mut.Unlock()
return ce, ok
}
func (c *cache) Cache() map[protocol.DeviceID]CacheEntry {
c.mut.Lock()
m := make(map[protocol.DeviceID]CacheEntry, len(c.entries))
for k, v := range c.entries {
m[k] = v
}
c.mut.Unlock()
return m
}