201 lines
5.8 KiB
Go
201 lines
5.8 KiB
Go
// Copyright 2015 The etcd Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package v2store
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import (
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"container/list"
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"path"
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"strings"
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"sync"
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"sync/atomic"
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"go.etcd.io/etcd/etcdserver/api/v2error"
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)
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// A watcherHub contains all subscribed watchers
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// watchers is a map with watched path as key and watcher as value
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// EventHistory keeps the old events for watcherHub. It is used to help
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// watcher to get a continuous event history. Or a watcher might miss the
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// event happens between the end of the first watch command and the start
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// of the second command.
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type watcherHub struct {
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// count must be the first element to keep 64-bit alignment for atomic
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// access
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count int64 // current number of watchers.
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mutex sync.Mutex
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watchers map[string]*list.List
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EventHistory *EventHistory
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}
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// newWatchHub creates a watcherHub. The capacity determines how many events we will
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// keep in the eventHistory.
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// Typically, we only need to keep a small size of history[smaller than 20K].
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// Ideally, it should smaller than 20K/s[max throughput] * 2 * 50ms[RTT] = 2000
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func newWatchHub(capacity int) *watcherHub {
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return &watcherHub{
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watchers: make(map[string]*list.List),
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EventHistory: newEventHistory(capacity),
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}
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}
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// Watch function returns a Watcher.
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// If recursive is true, the first change after index under key will be sent to the event channel of the watcher.
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// If recursive is false, the first change after index at key will be sent to the event channel of the watcher.
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// If index is zero, watch will start from the current index + 1.
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func (wh *watcherHub) watch(key string, recursive, stream bool, index, storeIndex uint64) (Watcher, *v2error.Error) {
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reportWatchRequest()
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event, err := wh.EventHistory.scan(key, recursive, index)
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if err != nil {
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err.Index = storeIndex
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return nil, err
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}
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w := &watcher{
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eventChan: make(chan *Event, 100), // use a buffered channel
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recursive: recursive,
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stream: stream,
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sinceIndex: index,
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startIndex: storeIndex,
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hub: wh,
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}
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wh.mutex.Lock()
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defer wh.mutex.Unlock()
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// If the event exists in the known history, append the EtcdIndex and return immediately
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if event != nil {
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ne := event.Clone()
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ne.EtcdIndex = storeIndex
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w.eventChan <- ne
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return w, nil
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}
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l, ok := wh.watchers[key]
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var elem *list.Element
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if ok { // add the new watcher to the back of the list
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elem = l.PushBack(w)
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} else { // create a new list and add the new watcher
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l = list.New()
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elem = l.PushBack(w)
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wh.watchers[key] = l
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}
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w.remove = func() {
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if w.removed { // avoid removing it twice
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return
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}
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w.removed = true
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l.Remove(elem)
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atomic.AddInt64(&wh.count, -1)
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reportWatcherRemoved()
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if l.Len() == 0 {
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delete(wh.watchers, key)
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}
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}
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atomic.AddInt64(&wh.count, 1)
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reportWatcherAdded()
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return w, nil
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}
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func (wh *watcherHub) add(e *Event) {
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wh.EventHistory.addEvent(e)
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}
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// notify function accepts an event and notify to the watchers.
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func (wh *watcherHub) notify(e *Event) {
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e = wh.EventHistory.addEvent(e) // add event into the eventHistory
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segments := strings.Split(e.Node.Key, "/")
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currPath := "/"
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// walk through all the segments of the path and notify the watchers
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// if the path is "/foo/bar", it will notify watchers with path "/",
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// "/foo" and "/foo/bar"
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for _, segment := range segments {
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currPath = path.Join(currPath, segment)
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// notify the watchers who interests in the changes of current path
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wh.notifyWatchers(e, currPath, false)
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}
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}
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func (wh *watcherHub) notifyWatchers(e *Event, nodePath string, deleted bool) {
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wh.mutex.Lock()
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defer wh.mutex.Unlock()
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l, ok := wh.watchers[nodePath]
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if ok {
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curr := l.Front()
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for curr != nil {
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next := curr.Next() // save reference to the next one in the list
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w, _ := curr.Value.(*watcher)
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originalPath := e.Node.Key == nodePath
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if (originalPath || !isHidden(nodePath, e.Node.Key)) && w.notify(e, originalPath, deleted) {
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if !w.stream { // do not remove the stream watcher
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// if we successfully notify a watcher
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// we need to remove the watcher from the list
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// and decrease the counter
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w.removed = true
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l.Remove(curr)
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atomic.AddInt64(&wh.count, -1)
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reportWatcherRemoved()
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}
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}
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curr = next // update current to the next element in the list
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}
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if l.Len() == 0 {
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// if we have notified all watcher in the list
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// we can delete the list
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delete(wh.watchers, nodePath)
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}
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}
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}
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// clone function clones the watcherHub and return the cloned one.
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// only clone the static content. do not clone the current watchers.
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func (wh *watcherHub) clone() *watcherHub {
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clonedHistory := wh.EventHistory.clone()
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return &watcherHub{
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EventHistory: clonedHistory,
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}
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}
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// isHidden checks to see if key path is considered hidden to watch path i.e. the
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// last element is hidden or it's within a hidden directory
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func isHidden(watchPath, keyPath string) bool {
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// When deleting a directory, watchPath might be deeper than the actual keyPath
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// For example, when deleting /foo we also need to notify watchers on /foo/bar.
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if len(watchPath) > len(keyPath) {
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return false
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}
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// if watch path is just a "/", after path will start without "/"
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// add a "/" to deal with the special case when watchPath is "/"
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afterPath := path.Clean("/" + keyPath[len(watchPath):])
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return strings.Contains(afterPath, "/_")
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}
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