1 // Copyright 2015 The etcd Authors 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 package v2store 16 17 type Watcher interface { 18 EventChan() chan *Event 19 StartIndex() uint64 // The EtcdIndex at which the Watcher was created 20 Remove() 21 } 22 23 type watcher struct { 24 eventChan chan *Event 25 stream bool 26 recursive bool 27 sinceIndex uint64 28 startIndex uint64 29 hub *watcherHub 30 removed bool 31 remove func() 32 } 33 34 func (w *watcher) EventChan() chan *Event { 35 return w.eventChan 36 } 37 38 func (w *watcher) StartIndex() uint64 { 39 return w.startIndex 40 } 41 42 // notify function notifies the watcher. If the watcher interests in the given path, 43 // the function will return true. 44 func (w *watcher) notify(e *Event, originalPath bool, deleted bool) bool { 45 // watcher is interested the path in three cases and under one condition 46 // the condition is that the event happens after the watcher's sinceIndex 47 48 // 1. the path at which the event happens is the path the watcher is watching at. 49 // For example if the watcher is watching at "/foo" and the event happens at "/foo", 50 // the watcher must be interested in that event. 51 52 // 2. the watcher is a recursive watcher, it interests in the event happens after 53 // its watching path. For example if watcher A watches at "/foo" and it is a recursive 54 // one, it will interest in the event happens at "/foo/bar". 55 56 // 3. when we delete a directory, we need to force notify all the watchers who watches 57 // at the file we need to delete. 58 // For example a watcher is watching at "/foo/bar". And we deletes "/foo". The watcher 59 // should get notified even if "/foo" is not the path it is watching. 60 if (w.recursive || originalPath || deleted) && e.Index() >= w.sinceIndex { 61 // We cannot block here if the eventChan capacity is full, otherwise 62 // etcd will hang. eventChan capacity is full when the rate of 63 // notifications are higher than our send rate. 64 // If this happens, we close the channel. 65 select { 66 case w.eventChan <- e: 67 default: 68 // We have missed a notification. Remove the watcher. 69 // Removing the watcher also closes the eventChan. 70 w.remove() 71 } 72 return true 73 } 74 return false 75 } 76 77 // Remove removes the watcher from watcherHub 78 // The actual remove function is guaranteed to only be executed once 79 func (w *watcher) Remove() { 80 w.hub.mutex.Lock() 81 defer w.hub.mutex.Unlock() 82 83 close(w.eventChan) 84 if w.remove != nil { 85 w.remove() 86 } 87 } 88 89 // nopWatcher is a watcher that receives nothing, always blocking. 90 type nopWatcher struct{} 91 92 func NewNopWatcher() Watcher { return &nopWatcher{} } 93 func (w *nopWatcher) EventChan() chan *Event { return nil } 94 func (w *nopWatcher) StartIndex() uint64 { return 0 } 95 func (w *nopWatcher) Remove() {} 96