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watcher.go
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watcher.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 (
"sync"
"github.com/coreos/etcd/storage/storagepb"
)
type Watcher interface {
// Watch watches the events happening or happened on the given key
// or key prefix from the given startRev.
// The whole event history can be watched unless compacted.
// If `prefix` is true, watch observes all events whose key prefix could be the given `key`.
// If `startRev` <=0, watch observes events after currentRev.
Watch(key []byte, prefix bool, startRev int64) CancelFunc
// Chan returns a chan. All watched events will be sent to the returned chan.
Chan() <-chan storagepb.Event
// Close closes the WatchChan and release all related resources.
Close()
}
// watcher contains a collection of watching that share
// one chan to send out watched events and other control events.
type watcher struct {
watchable watchable
ch chan storagepb.Event
mu sync.Mutex // guards fields below it
closed bool
cancels []CancelFunc
}
// TODO: return error if ws is closed?
func (ws *watcher) Watch(key []byte, prefix bool, startRev int64) CancelFunc {
_, c := ws.watchable.watch(key, prefix, startRev, ws.ch)
ws.mu.Lock()
defer ws.mu.Unlock()
if ws.closed {
return nil
}
// TODO: cancelFunc needs to be removed from the cancels when it is called.
ws.cancels = append(ws.cancels, c)
return c
}
func (ws *watcher) Chan() <-chan storagepb.Event {
return ws.ch
}
func (ws *watcher) Close() {
ws.mu.Lock()
defer ws.mu.Unlock()
for _, cancel := range ws.cancels {
cancel()
}
ws.closed = true
close(ws.ch)
watcherGauge.Dec()
}