Add cache package.

pkg/client/cache/fifo.go

@@ -0,0 +1,107 @@
+/*
+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 (
+	"sync"
+)
+
+type FIFO struct {
+	lock  sync.RWMutex
+	cond  sync.Cond
+	items map[string]interface{}
+	queue []string
+}
+
+// Add inserts an item, and puts it in the queue.
+func (f *FIFO) Add(ID string, obj interface{}) {
+	f.lock.Lock()
+	defer f.lock.Unlock()
+	f.items[ID] = obj
+	f.queue = append(f.queue, ID)
+	f.cond.Broadcast()
+}
+
+// Update updates an item, and adds it to the queue.
+func (f *FIFO) Update(ID string, obj interface{}) {
+	f.lock.Lock()
+	defer f.lock.Unlock()
+	f.items[ID] = obj
+	f.queue = append(f.queue, ID)
+	f.cond.Broadcast()
+}
+
+// Delete removes an item. It doesn't add it to the queue, because
+// this implementation assumes the consumer only cares about the objects,
+// not the order in which they were created/added.
+func (f *FIFO) Delete(ID string, obj interface{}) {
+	f.lock.Lock()
+	defer f.lock.Unlock()
+	delete(f.items, ID)
+}
+
+// List returns a list of all the items.
+func (f *FIFO) List() []interface{} {
+	f.lock.RLock()
+	defer f.lock.RUnlock()
+	list := make([]interface{}, 0, len(f.items))
+	for _, item := range f.items {
+		list = append(list, item)
+	}
+	return list
+}
+
+// Get returns the requested item, or sets exists=false.
+func (f *FIFO) Get(ID string) (item interface{}, exists bool) {
+	f.lock.RLock()
+	defer f.lock.RUnlock()
+	item, exists = f.items[ID]
+	return item, exists
+}
+
+// Pop waits until an item is ready and returns it. If multiple items are
+// ready, they are returned in the order in which they were added/updated.
+// The item is removed from the queue (and the store) before it is returned,
+// so if you don't succesfully process it, you need to add it back with Add().
+func (f *FIFO) Pop() interface{} {
+	f.lock.Lock()
+	defer f.lock.Unlock()
+	for {
+		for len(f.queue) == 0 {
+			f.cond.Wait()
+		}
+		id := f.queue[0]
+		f.queue = f.queue[1:]
+		item, ok := f.items[id]
+		if !ok {
+			// Item may have been deleted subsequently.
+			continue
+		}
+		return item
+	}
+}
+
+// NewFIFOStore returns a Store which can be used to queue up items to
+// process.
+func NewFIFOStore() *FIFO {
+	f := &FIFO{
+		items: map[string]interface{}{},
+		queue: []string{},
+	}
+	f.cond.L = &f.lock
+	return f
+}