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watcher_group.go
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watcher_group.go
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// Copyright 2016 The etcd Authors
//
// 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 mvcc
import (
"math"
"github.com/coreos/etcd/mvcc/mvccpb"
"github.com/coreos/etcd/pkg/adt"
)
var (
// watchBatchMaxRevs is the maximum distinct revisions that
// may be sent to an unsynced watcher at a time. Declared as
// var instead of const for testing purposes.
watchBatchMaxRevs = 1000
)
type eventBatch struct {
// evs is a batch of revision-ordered events
evs []mvccpb.Event
// revs is the minimum unique revisions observed for this batch
revs int
// moreRev is first revision with more events following this batch
moreRev int64
}
func (eb *eventBatch) add(ev mvccpb.Event) {
if eb.revs > watchBatchMaxRevs {
// maxed out batch size
return
}
if len(eb.evs) == 0 {
// base case
eb.revs = 1
eb.evs = append(eb.evs, ev)
return
}
// revision accounting
ebRev := eb.evs[len(eb.evs)-1].Kv.ModRevision
evRev := ev.Kv.ModRevision
if evRev > ebRev {
eb.revs++
if eb.revs > watchBatchMaxRevs {
eb.moreRev = evRev
return
}
}
eb.evs = append(eb.evs, ev)
}
type watcherBatch map[*watcher]*eventBatch
func (wb watcherBatch) add(w *watcher, ev mvccpb.Event) {
eb := wb[w]
if eb == nil {
eb = &eventBatch{}
wb[w] = eb
}
eb.add(ev)
}
// newWatcherBatch maps watchers to their matched events. It enables quick
// events look up by watcher.
func newWatcherBatch(wg *watcherGroup, evs []mvccpb.Event) watcherBatch {
if len(wg.watchers) == 0 {
return nil
}
wb := make(watcherBatch)
for _, ev := range evs {
for w := range wg.watcherSetByKey(string(ev.Kv.Key)) {
if ev.Kv.ModRevision >= w.minRev {
// don't double notify
wb.add(w, ev)
}
}
}
return wb
}
type watcherSet map[*watcher]struct{}
func (w watcherSet) add(wa *watcher) {
if _, ok := w[wa]; ok {
panic("add watcher twice!")
}
w[wa] = struct{}{}
}
func (w watcherSet) union(ws watcherSet) {
for wa := range ws {
w.add(wa)
}
}
func (w watcherSet) delete(wa *watcher) {
if _, ok := w[wa]; !ok {
panic("removing missing watcher!")
}
delete(w, wa)
}
type watcherSetByKey map[string]watcherSet
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) delete(wa *watcher) bool {
k := string(wa.key)
if v, ok := w[k]; ok {
if _, ok := v[wa]; ok {
delete(v, wa)
if len(v) == 0 {
// remove the set; nothing left
delete(w, k)
}
return true
}
}
return false
}
// watcherGroup is a collection of watchers organized by their ranges
type watcherGroup struct {
// keyWatchers has the watchers that watch on a single key
keyWatchers watcherSetByKey
// ranges has the watchers that watch a range; it is sorted by interval
ranges adt.IntervalTree
// watchers is the set of all watchers
watchers watcherSet
}
func newWatcherGroup() watcherGroup {
return watcherGroup{
keyWatchers: make(watcherSetByKey),
watchers: make(watcherSet),
}
}
// add puts a watcher in the group.
func (wg *watcherGroup) add(wa *watcher) {
wg.watchers.add(wa)
if wa.end == nil {
wg.keyWatchers.add(wa)
return
}
// interval already registered?
ivl := adt.NewStringAffineInterval(string(wa.key), string(wa.end))
if iv := wg.ranges.Find(ivl); iv != nil {
iv.Val.(watcherSet).add(wa)
return
}
// not registered, put in interval tree
ws := make(watcherSet)
ws.add(wa)
wg.ranges.Insert(ivl, ws)
}
// contains is whether the given key has a watcher in the group.
func (wg *watcherGroup) contains(key string) bool {
_, ok := wg.keyWatchers[key]
return ok || wg.ranges.Intersects(adt.NewStringAffinePoint(key))
}
// size gives the number of unique watchers in the group.
func (wg *watcherGroup) size() int { return len(wg.watchers) }
// delete removes a watcher from the group.
func (wg *watcherGroup) delete(wa *watcher) bool {
if _, ok := wg.watchers[wa]; !ok {
return false
}
wg.watchers.delete(wa)
if wa.end == nil {
wg.keyWatchers.delete(wa)
return true
}
ivl := adt.NewStringAffineInterval(string(wa.key), string(wa.end))
iv := wg.ranges.Find(ivl)
if iv == nil {
return false
}
ws := iv.Val.(watcherSet)
delete(ws, wa)
if len(ws) == 0 {
// remove interval missing watchers
if ok := wg.ranges.Delete(ivl); !ok {
panic("could not remove watcher from interval tree")
}
}
return true
}
// choose selects watchers from the watcher group to update
func (wg *watcherGroup) choose(maxWatchers int, curRev, compactRev int64) (*watcherGroup, int64) {
if len(wg.watchers) < maxWatchers {
return wg, wg.chooseAll(curRev, compactRev)
}
ret := newWatcherGroup()
for w := range wg.watchers {
if maxWatchers <= 0 {
break
}
maxWatchers--
ret.add(w)
}
return &ret, ret.chooseAll(curRev, compactRev)
}
func (wg *watcherGroup) chooseAll(curRev, compactRev int64) int64 {
minRev := int64(math.MaxInt64)
for w := range wg.watchers {
if w.minRev > curRev {
panic("watcher current revision should not exceed current revision")
}
if w.minRev < compactRev {
select {
case w.ch <- WatchResponse{WatchID: w.id, CompactRevision: compactRev}:
w.compacted = true
wg.delete(w)
default:
// retry next time
}
continue
}
if minRev > w.minRev {
minRev = w.minRev
}
}
return minRev
}
// watcherSetByKey gets the set of watchers that receive events on the given key.
func (wg *watcherGroup) watcherSetByKey(key string) watcherSet {
wkeys := wg.keyWatchers[key]
wranges := wg.ranges.Stab(adt.NewStringAffinePoint(key))
// zero-copy cases
switch {
case len(wranges) == 0:
// no need to merge ranges or copy; reuse single-key set
return wkeys
case len(wranges) == 0 && len(wkeys) == 0:
return nil
case len(wranges) == 1 && len(wkeys) == 0:
return wranges[0].Val.(watcherSet)
}
// copy case
ret := make(watcherSet)
ret.union(wg.keyWatchers[key])
for _, item := range wranges {
ret.union(item.Val.(watcherSet))
}
return ret
}