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cache.go
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cache.go
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// 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 https://mozilla.org/MPL/2.0/.
package discover
import (
"sort"
stdsync "sync"
"time"
"github.com/syncthing/syncthing/lib/protocol"
"github.com/syncthing/syncthing/lib/sync"
"github.com/syncthing/syncthing/lib/util"
"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 successful 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 interface {
FinderService
Add(finder Finder, cacheTime, negCacheTime time.Duration)
ChildErrors() map[string]error
}
type cachingMux struct {
*suture.Supervisor
finders []cachedFinder
caches []*cache
mut sync.RWMutex
}
// A cachedFinder is a Finder with associated cache timeouts.
type cachedFinder struct {
Finder
cacheTime time.Duration
negCacheTime time.Duration
}
// An error may implement cachedError, in which case it will be interrogated
// to see how long we should cache the error. This overrides the default
// negative cache time.
type cachedError interface {
CacheFor() time.Duration
}
func NewCachingMux() CachingMux {
return &cachingMux{
Supervisor: suture.New("discover.cachingMux", suture.Spec{
PassThroughPanics: true,
}),
mut: sync.NewRWMutex(),
}
}
// 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 service, ok := finder.(suture.Service); ok {
m.Supervisor.Add(service)
}
}
// 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) (addresses []string, err error) {
m.mut.RLock()
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.
l.Debugln("cached discovery entry for", deviceID, "at", finder)
l.Debugln(" cache:", cacheEntry)
addresses = append(addresses, cacheEntry.Addresses...)
continue
}
valid := time.Now().Before(cacheEntry.validUntil) || time.Since(cacheEntry.when) < finder.negCacheTime
if !cacheEntry.found && valid {
// It's a negative, valid entry. We should not make another
// attempt right now.
l.Debugln("negative cache entry for", deviceID, "at", finder, "valid until", cacheEntry.when.Add(finder.negCacheTime), "or", cacheEntry.validUntil)
continue
}
// It's expired. Ignore and continue.
}
// Perform the actual lookup and cache the result.
if addrs, err := finder.Lookup(deviceID); err == nil {
l.Debugln("lookup for", deviceID, "at", finder)
l.Debugln(" addresses:", addrs)
addresses = append(addresses, addrs...)
m.caches[i].Set(deviceID, CacheEntry{
Addresses: addrs,
when: time.Now(),
found: len(addrs) > 0,
})
} else {
// Lookup returned error, add a negative cache entry.
entry := CacheEntry{
when: time.Now(),
found: false,
}
if err, ok := err.(cachedError); ok {
entry.validUntil = time.Now().Add(err.CacheFor())
}
m.caches[i].Set(deviceID, entry)
}
}
m.mut.RUnlock()
addresses = util.UniqueTrimmedStrings(addresses)
sort.Strings(addresses)
l.Debugln("lookup results for", deviceID)
l.Debugln(" addresses: ", addresses)
return addresses, nil
}
func (m *cachingMux) String() string {
return "discovery cache"
}
func (m *cachingMux) Error() error {
return nil
}
func (m *cachingMux) ChildErrors() map[string]error {
children := make(map[string]error, len(m.finders))
m.mut.RLock()
for _, f := range m.finders {
children[f.String()] = f.Error()
}
m.mut.RUnlock()
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.RLock()
for i := range m.finders {
// Each finder[i] has a corresponding cache at cache[i]. Go through
// it and populate the total, appending any addresses and keeping
// the newest "when" time. We skip any negative cache entries.
for k, v := range m.caches[i].Cache() {
if v.found {
cur := res[k]
if v.when.After(cur.when) {
cur.when = v.when
}
cur.Addresses = append(cur.Addresses, v.Addresses...)
res[k] = cur
}
}
// Then ask the finder itself for its 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 its current state.
for k, v := range m.finders[i].Cache() {
if v.found {
cur := res[k]
if v.when.After(cur.when) {
cur.when = v.when
}
cur.Addresses = append(cur.Addresses, v.Addresses...)
res[k] = cur
}
}
}
m.mut.RUnlock()
for k, v := range res {
v.Addresses = util.UniqueTrimmedStrings(v.Addresses)
res[k] = v
}
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
}