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watchable_store.go
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watchable_store.go
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// Copyright 2015 CoreOS, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package storage
import (
"log"
"math"
"strings"
"sync"
"time"
"github.com/coreos/etcd/lease"
"github.com/coreos/etcd/storage/backend"
"github.com/coreos/etcd/storage/storagepb"
)
const (
// chanBufLen is the length of the buffered chan
// for sending out watched events.
// TODO: find a good buf value. 1024 is just a random one that
// seems to be reasonable.
chanBufLen = 1024
)
type (
watcherSetByKey map[string]watcherSet
watcherSet map[*watcher]struct{}
)
func (w watcherSet) add(wa *watcher) {
if _, ok := w[wa]; ok {
panic("add watcher twice!")
}
w[wa] = struct{}{}
}
func (w watcherSetByKey) add(wa *watcher) {
set := w[string(wa.key)]
if set == nil {
set = make(watcherSet)
w[string(wa.key)] = set
}
set.add(wa)
}
func (w watcherSetByKey) getSetByKey(key string) (watcherSet, bool) {
set, ok := w[key]
return set, ok
}
func (w watcherSetByKey) delete(wa *watcher) bool {
k := string(wa.key)
if v, ok := w[k]; ok {
if _, ok := v[wa]; ok {
delete(v, wa)
// if there is nothing in the set,
// remove the set
if len(v) == 0 {
delete(w, k)
}
return true
}
}
return false
}
type watchable interface {
watch(key []byte, prefix bool, startRev int64, id WatchID, ch chan<- WatchResponse) (*watcher, cancelFunc)
rev() int64
}
type watchableStore struct {
mu sync.Mutex
*store
// contains all unsynced watchers that needs to sync with events that have happened
unsynced watcherSetByKey
// contains all synced watchers that are in sync with the progress of the store.
// The key of the map is the key that the watcher watches on.
synced watcherSetByKey
stopc chan struct{}
wg sync.WaitGroup
}
// cancelFunc updates unsynced and synced maps when running
// cancel operations.
type cancelFunc func()
func newWatchableStore(b backend.Backend, le lease.Lessor) *watchableStore {
s := &watchableStore{
store: NewStore(b, le),
unsynced: make(watcherSetByKey),
synced: make(watcherSetByKey),
stopc: make(chan struct{}),
}
if s.le != nil {
// use this store as the deleter so revokes trigger watch events
s.le.SetRangeDeleter(s)
}
s.wg.Add(1)
go s.syncWatchersLoop()
return s
}
func (s *watchableStore) Put(key, value []byte, lease lease.LeaseID) (rev int64) {
s.mu.Lock()
defer s.mu.Unlock()
rev = s.store.Put(key, value, lease)
changes := s.store.getChanges()
if len(changes) != 1 {
log.Panicf("unexpected len(changes) != 1 after put")
}
ev := storagepb.Event{
Type: storagepb.PUT,
Kv: &changes[0],
}
s.notify(rev, []storagepb.Event{ev})
return rev
}
func (s *watchableStore) DeleteRange(key, end []byte) (n, rev int64) {
s.mu.Lock()
defer s.mu.Unlock()
n, rev = s.store.DeleteRange(key, end)
changes := s.store.getChanges()
if len(changes) != int(n) {
log.Panicf("unexpected len(changes) != n after deleteRange")
}
if n == 0 {
return n, rev
}
evs := make([]storagepb.Event, n)
for i, change := range changes {
evs[i] = storagepb.Event{
Type: storagepb.DELETE,
Kv: &change}
evs[i].Kv.ModRevision = rev
}
s.notify(rev, evs)
return n, rev
}
func (s *watchableStore) TxnBegin() int64 {
s.mu.Lock()
return s.store.TxnBegin()
}
func (s *watchableStore) TxnEnd(txnID int64) error {
err := s.store.TxnEnd(txnID)
if err != nil {
return err
}
changes := s.getChanges()
if len(changes) == 0 {
s.mu.Unlock()
return nil
}
rev := s.store.Rev()
evs := make([]storagepb.Event, len(changes))
for i, change := range changes {
switch change.Value {
case nil:
evs[i] = storagepb.Event{
Type: storagepb.DELETE,
Kv: &changes[i]}
evs[i].Kv.ModRevision = rev
default:
evs[i] = storagepb.Event{
Type: storagepb.PUT,
Kv: &changes[i]}
}
}
s.notify(rev, evs)
s.mu.Unlock()
return nil
}
func (s *watchableStore) Close() error {
close(s.stopc)
s.wg.Wait()
return s.store.Close()
}
func (s *watchableStore) NewWatchStream() WatchStream {
watchStreamGauge.Inc()
return &watchStream{
watchable: s,
ch: make(chan WatchResponse, chanBufLen),
cancels: make(map[WatchID]cancelFunc),
}
}
func (s *watchableStore) watch(key []byte, prefix bool, startRev int64, id WatchID, ch chan<- WatchResponse) (*watcher, cancelFunc) {
s.mu.Lock()
defer s.mu.Unlock()
wa := &watcher{
key: key,
prefix: prefix,
cur: startRev,
id: id,
ch: ch,
}
s.store.mu.Lock()
synced := startRev > s.store.currentRev.main || startRev == 0
if synced {
wa.cur = s.store.currentRev.main + 1
}
s.store.mu.Unlock()
if synced {
if startRev > wa.cur {
panic("can't watch past sync revision")
}
s.synced.add(wa)
} else {
slowWatcherGauge.Inc()
s.unsynced.add(wa)
}
watcherGauge.Inc()
cancel := cancelFunc(func() {
s.mu.Lock()
defer s.mu.Unlock()
// remove references of the watcher
if s.unsynced.delete(wa) {
slowWatcherGauge.Dec()
watcherGauge.Dec()
return
}
if s.synced.delete(wa) {
watcherGauge.Dec()
}
// If we cannot find it, it should have finished watch.
})
return wa, cancel
}
// syncWatchersLoop syncs the watcher in the unsynced map every 100ms.
func (s *watchableStore) syncWatchersLoop() {
defer s.wg.Done()
for {
s.mu.Lock()
s.syncWatchers()
s.mu.Unlock()
select {
case <-time.After(100 * time.Millisecond):
case <-s.stopc:
return
}
}
}
// syncWatchers periodically syncs unsynced watchers by: Iterate all unsynced
// watchers to get the minimum revision within its range, skipping the
// watcher if its current revision is behind the compact revision of the
// store. And use this minimum revision to get all key-value pairs. Then send
// those events to watchers.
func (s *watchableStore) syncWatchers() {
s.store.mu.Lock()
defer s.store.mu.Unlock()
if len(s.unsynced) == 0 {
return
}
// in order to find key-value pairs from unsynced watchers, we need to
// find min revision index, and these revisions can be used to
// query the backend store of key-value pairs
prefixes, minRev := s.scanUnsync()
curRev := s.store.currentRev.main
minBytes, maxBytes := newRevBytes(), newRevBytes()
revToBytes(revision{main: minRev}, minBytes)
revToBytes(revision{main: curRev + 1}, maxBytes)
// UnsafeRange returns keys and values. And in boltdb, keys are revisions.
// values are actual key-value pairs in backend.
tx := s.store.b.BatchTx()
tx.Lock()
revs, vs := tx.UnsafeRange(keyBucketName, minBytes, maxBytes, 0)
evs := kvsToEvents(revs, vs, s.unsynced, prefixes)
tx.Unlock()
for w, es := range newWatcherToEventMap(s.unsynced, evs) {
select {
// s.store.Rev also uses Lock, so just return directly
case w.ch <- WatchResponse{WatchID: w.id, Events: es, Revision: s.store.currentRev.main}:
pendingEventsGauge.Add(float64(len(es)))
default:
// TODO: handle the full unsynced watchers.
// continue to process other watchers for now, the full ones
// will be processed next time and hopefully it will not be full.
continue
}
w.cur = curRev
s.synced.add(w)
s.unsynced.delete(w)
}
slowWatcherGauge.Set(float64(len(s.unsynced)))
}
func (s *watchableStore) scanUnsync() (prefixes map[string]struct{}, minRev int64) {
curRev := s.store.currentRev.main
compactionRev := s.store.compactMainRev
prefixes = make(map[string]struct{})
minRev = int64(math.MaxInt64)
for _, set := range s.unsynced {
for w := range set {
k := string(w.key)
if w.cur > curRev {
panic("watcher current revision should not exceed current revision")
}
if w.cur < compactionRev {
select {
case w.ch <- WatchResponse{WatchID: w.id, CompactRevision: compactionRev}:
s.unsynced.delete(w)
default:
// retry next time
}
continue
}
if minRev > w.cur {
minRev = w.cur
}
if w.prefix {
prefixes[k] = struct{}{}
}
}
}
return prefixes, minRev
}
// kvsToEvents gets all events for the watchers from all key-value pairs
func kvsToEvents(revs, vals [][]byte, wsk watcherSetByKey, pfxs map[string]struct{}) (evs []storagepb.Event) {
for i, v := range vals {
var kv storagepb.KeyValue
if err := kv.Unmarshal(v); err != nil {
log.Panicf("storage: cannot unmarshal event: %v", err)
}
k := string(kv.Key)
if _, ok := wsk.getSetByKey(k); !ok && !matchPrefix(k, pfxs) {
continue
}
ty := storagepb.PUT
if isTombstone(revs[i]) {
ty = storagepb.DELETE
// patch in mod revision so watchers won't skip
kv.ModRevision = bytesToRev(revs[i]).main
}
evs = append(evs, storagepb.Event{Kv: &kv, Type: ty})
}
return evs
}
// notify notifies the fact that given event at the given rev just happened to
// watchers that watch on the key of the event.
func (s *watchableStore) notify(rev int64, evs []storagepb.Event) {
we := newWatcherToEventMap(s.synced, evs)
for _, wm := range s.synced {
for w := range wm {
es, ok := we[w]
if !ok {
continue
}
select {
case w.ch <- WatchResponse{WatchID: w.id, Events: es, Revision: s.Rev()}:
pendingEventsGauge.Add(float64(len(es)))
default:
// move slow watcher to unsynced
w.cur = rev
s.unsynced.add(w)
delete(wm, w)
slowWatcherGauge.Inc()
}
}
}
}
func (s *watchableStore) rev() int64 { return s.store.Rev() }
type watcher struct {
// the watcher key
key []byte
// prefix indicates if watcher is on a key or a prefix.
// If prefix is true, the watcher is on a prefix.
prefix bool
// cur is the current watcher revision.
// If cur is behind the current revision of the KV,
// watcher is unsynced and needs to catch up.
cur int64
id WatchID
// a chan to send out the watch response.
// The chan might be shared with other watchers.
ch chan<- WatchResponse
}
// newWatcherToEventMap creates a map that has watcher as key and events as
// value. It enables quick events look up by watcher.
func newWatcherToEventMap(sm watcherSetByKey, evs []storagepb.Event) map[*watcher][]storagepb.Event {
watcherToEvents := make(map[*watcher][]storagepb.Event)
for _, ev := range evs {
key := string(ev.Kv.Key)
// check all prefixes of the key to notify all corresponded watchers
for i := 0; i <= len(key); i++ {
for w := range sm[key[:i]] {
// don't double notify
if ev.Kv.ModRevision < w.cur {
continue
}
// the watcher needs to be notified when either it watches prefix or
// the key is exactly matched.
if !w.prefix && i != len(ev.Kv.Key) {
continue
}
watcherToEvents[w] = append(watcherToEvents[w], ev)
}
}
}
return watcherToEvents
}
// matchPrefix returns true if key has any matching prefix
// from prefixes map.
func matchPrefix(key string, prefixes map[string]struct{}) bool {
for p := range prefixes {
if strings.HasPrefix(key, p) {
return true
}
}
return false
}