Add poller to cache.

pkg/client/cache/poller.go

@@ -0,0 +1,81 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+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 cache
+
+import (
+	"time"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/util"
+	"github.com/golang/glog"
+)
+
+// Enumerator should be able to return the list of objects to be synced with
+// one object at a time.
+type Enumerator interface {
+	Len() int
+	Get(index int) (ID string, object interface{})
+}
+
+// GetFunc should return an enumerator that you wish the Poller to proccess.
+type GetFunc func() (Enumerator, error)
+
+// Poller is like Reflector, but it periodically polls instead of watching.
+// This is intended to be a workaround for api objects that don't yet support
+// watching.
+type Poller struct {
+	getFunc GetFunc
+	period  time.Duration
+	store   Store
+}
+
+// NewPoller constructs a new poller. Note that polling probably doesn't make much
+// sense to use along with the FIFO queue. The returned Poller will call getFunc and
+// sync the objects in 'store' with the returned Enumerator, waiting 'period' between
+// each call. It probably only makes sense to use a poller if you're treating the
+// store as read-only.
+func NewPoller(getFunc GetFunc, period time.Duration, store Store) *Poller {
+	return &Poller{
+		getFunc: getFunc,
+		period:  period,
+		store:   store,
+	}
+}
+
+// Run begins polling. It starts a goroutine and returns immediately.
+func (p *Poller) Run() {
+	go util.Forever(func() {
+		e, err := p.getFunc()
+		if err != nil {
+			glog.Errorf("failed to list: %v", err)
+			return
+		}
+		p.sync(e)
+	}, p.period)
+}
+
+func (p *Poller) sync(e Enumerator) {
+	current := p.store.Contains()
+	for i := 0; i < e.Len(); i++ {
+		id, object := e.Get(i)
+		p.store.Update(id, object)
+		current.Delete(id)
+	}
+	// Delete all the objects not found.
+	for id := range current {
+		p.store.Delete(id)
+	}
+}