khenaidoo | d948f77 | 2021-08-11 17:49:24 -0400 | [diff] [blame] | 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 mvcc |
| 16 | |
| 17 | import ( |
| 18 | "bytes" |
| 19 | "errors" |
| 20 | "sync" |
| 21 | |
| 22 | "github.com/coreos/etcd/mvcc/mvccpb" |
| 23 | ) |
| 24 | |
| 25 | var ( |
| 26 | ErrWatcherNotExist = errors.New("mvcc: watcher does not exist") |
| 27 | ) |
| 28 | |
| 29 | type WatchID int64 |
| 30 | |
| 31 | // FilterFunc returns true if the given event should be filtered out. |
| 32 | type FilterFunc func(e mvccpb.Event) bool |
| 33 | |
| 34 | type WatchStream interface { |
| 35 | // Watch creates a watcher. The watcher watches the events happening or |
| 36 | // happened on the given key or range [key, end) from the given startRev. |
| 37 | // |
| 38 | // The whole event history can be watched unless compacted. |
| 39 | // If `startRev` <=0, watch observes events after currentRev. |
| 40 | // |
| 41 | // The returned `id` is the ID of this watcher. It appears as WatchID |
| 42 | // in events that are sent to the created watcher through stream channel. |
| 43 | // |
| 44 | Watch(key, end []byte, startRev int64, fcs ...FilterFunc) WatchID |
| 45 | |
| 46 | // Chan returns a chan. All watch response will be sent to the returned chan. |
| 47 | Chan() <-chan WatchResponse |
| 48 | |
| 49 | // RequestProgress requests the progress of the watcher with given ID. The response |
| 50 | // will only be sent if the watcher is currently synced. |
| 51 | // The responses will be sent through the WatchRespone Chan attached |
| 52 | // with this stream to ensure correct ordering. |
| 53 | // The responses contains no events. The revision in the response is the progress |
| 54 | // of the watchers since the watcher is currently synced. |
| 55 | RequestProgress(id WatchID) |
| 56 | |
| 57 | // Cancel cancels a watcher by giving its ID. If watcher does not exist, an error will be |
| 58 | // returned. |
| 59 | Cancel(id WatchID) error |
| 60 | |
| 61 | // Close closes Chan and release all related resources. |
| 62 | Close() |
| 63 | |
| 64 | // Rev returns the current revision of the KV the stream watches on. |
| 65 | Rev() int64 |
| 66 | } |
| 67 | |
| 68 | type WatchResponse struct { |
| 69 | // WatchID is the WatchID of the watcher this response sent to. |
| 70 | WatchID WatchID |
| 71 | |
| 72 | // Events contains all the events that needs to send. |
| 73 | Events []mvccpb.Event |
| 74 | |
| 75 | // Revision is the revision of the KV when the watchResponse is created. |
| 76 | // For a normal response, the revision should be the same as the last |
| 77 | // modified revision inside Events. For a delayed response to a unsynced |
| 78 | // watcher, the revision is greater than the last modified revision |
| 79 | // inside Events. |
| 80 | Revision int64 |
| 81 | |
| 82 | // CompactRevision is set when the watcher is cancelled due to compaction. |
| 83 | CompactRevision int64 |
| 84 | } |
| 85 | |
| 86 | // watchStream contains a collection of watchers that share |
| 87 | // one streaming chan to send out watched events and other control events. |
| 88 | type watchStream struct { |
| 89 | watchable watchable |
| 90 | ch chan WatchResponse |
| 91 | |
| 92 | mu sync.Mutex // guards fields below it |
| 93 | // nextID is the ID pre-allocated for next new watcher in this stream |
| 94 | nextID WatchID |
| 95 | closed bool |
| 96 | cancels map[WatchID]cancelFunc |
| 97 | watchers map[WatchID]*watcher |
| 98 | } |
| 99 | |
| 100 | // Watch creates a new watcher in the stream and returns its WatchID. |
| 101 | // TODO: return error if ws is closed? |
| 102 | func (ws *watchStream) Watch(key, end []byte, startRev int64, fcs ...FilterFunc) WatchID { |
| 103 | // prevent wrong range where key >= end lexicographically |
| 104 | // watch request with 'WithFromKey' has empty-byte range end |
| 105 | if len(end) != 0 && bytes.Compare(key, end) != -1 { |
| 106 | return -1 |
| 107 | } |
| 108 | |
| 109 | ws.mu.Lock() |
| 110 | defer ws.mu.Unlock() |
| 111 | if ws.closed { |
| 112 | return -1 |
| 113 | } |
| 114 | |
| 115 | id := ws.nextID |
| 116 | ws.nextID++ |
| 117 | |
| 118 | w, c := ws.watchable.watch(key, end, startRev, id, ws.ch, fcs...) |
| 119 | |
| 120 | ws.cancels[id] = c |
| 121 | ws.watchers[id] = w |
| 122 | return id |
| 123 | } |
| 124 | |
| 125 | func (ws *watchStream) Chan() <-chan WatchResponse { |
| 126 | return ws.ch |
| 127 | } |
| 128 | |
| 129 | func (ws *watchStream) Cancel(id WatchID) error { |
| 130 | ws.mu.Lock() |
| 131 | cancel, ok := ws.cancels[id] |
| 132 | w := ws.watchers[id] |
| 133 | ok = ok && !ws.closed |
| 134 | ws.mu.Unlock() |
| 135 | |
| 136 | if !ok { |
| 137 | return ErrWatcherNotExist |
| 138 | } |
| 139 | cancel() |
| 140 | |
| 141 | ws.mu.Lock() |
| 142 | // The watch isn't removed until cancel so that if Close() is called, |
| 143 | // it will wait for the cancel. Otherwise, Close() could close the |
| 144 | // watch channel while the store is still posting events. |
| 145 | if ww := ws.watchers[id]; ww == w { |
| 146 | delete(ws.cancels, id) |
| 147 | delete(ws.watchers, id) |
| 148 | } |
| 149 | ws.mu.Unlock() |
| 150 | |
| 151 | return nil |
| 152 | } |
| 153 | |
| 154 | func (ws *watchStream) Close() { |
| 155 | ws.mu.Lock() |
| 156 | defer ws.mu.Unlock() |
| 157 | |
| 158 | for _, cancel := range ws.cancels { |
| 159 | cancel() |
| 160 | } |
| 161 | ws.closed = true |
| 162 | close(ws.ch) |
| 163 | watchStreamGauge.Dec() |
| 164 | } |
| 165 | |
| 166 | func (ws *watchStream) Rev() int64 { |
| 167 | ws.mu.Lock() |
| 168 | defer ws.mu.Unlock() |
| 169 | return ws.watchable.rev() |
| 170 | } |
| 171 | |
| 172 | func (ws *watchStream) RequestProgress(id WatchID) { |
| 173 | ws.mu.Lock() |
| 174 | w, ok := ws.watchers[id] |
| 175 | ws.mu.Unlock() |
| 176 | if !ok { |
| 177 | return |
| 178 | } |
| 179 | ws.watchable.progress(w) |
| 180 | } |