Add mux type to watch package

pkg/watch/mux.go

@@ -0,0 +1,138 @@
+/*
+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 watch
+
+import (
+	"sync"
+)
+
+// Mux distributes event notifications among any number of watchers.
+type Mux struct {
+	lock sync.Mutex
+
+	watchers    map[int64]*muxWatcher
+	nextWatcher int64
+
+	incoming chan Event
+}
+
+// NewMux creates a new Mux. queueLength is the maximum number of events to queue.
+// When queueLength is 0, Action will block until any prior event has been
+// completely distributed. It is guaranteed that events will be distibuted in the
+// order in which they occurr, but the order in which a single event is distributed
+// among all of the watchers is unspecified.
+func NewMux(queueLength int) *Mux {
+	m := &Mux{
+		watchers: map[int64]*muxWatcher{},
+		incoming: make(chan Event, queueLength),
+	}
+	go m.loop()
+	return m
+}
+
+// Watch adds a new watcher to the list and returns an Interface for it.
+// Note: new watchers will only receive new events. They won't get an entire history
+// of previous events.
+func (m *Mux) Watch() Interface {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	id := m.nextWatcher
+	m.nextWatcher++
+	w := &muxWatcher{
+		result: make(chan Event),
+		id:     id,
+		m:      m,
+	}
+	m.watchers[id] = w
+	return w
+}
+
+// stopWatching stops the given watcher and removes it from the list.
+func (m *Mux) stopWatching(id int64) {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	w, ok := m.watchers[id]
+	if !ok {
+		// No need to do anything, it's already been removed from the list.
+		return
+	}
+	delete(m.watchers, id)
+	close(w.result)
+}
+
+// closeAll disconnects all watchers (presumably in response to a Shutdown call).
+func (m *Mux) closeAll() {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	for _, w := range m.watchers {
+		close(w.result)
+	}
+	// Delete everything from the map, since presence/absence in the map is used
+	// by stopWatching to avoid double-closing the channel.
+	m.watchers = map[int64]*muxWatcher{}
+}
+
+// Action distributes the given event among all watchers.
+func (m *Mux) Action(action EventType, obj interface{}) {
+	m.incoming <- Event{action, obj}
+}
+
+// Shutdown disconnects all watchers (but any queued events will still be distributed).
+// You must not call Action after calling Shutdown.
+func (m *Mux) Shutdown() {
+	close(m.incoming)
+}
+
+// loop recieves from m.incoming and distributes to all watchers.
+func (m *Mux) loop() {
+	// Deliberately not catching crashes here. Yes, bring down the process if there's a
+	// bug in watch.Mux.
+	for {
+		event, ok := <-m.incoming
+		if !ok {
+			break
+		}
+		m.distribute(event)
+	}
+	m.closeAll()
+}
+
+// distribute sends event to all watchers. Blocking.
+func (m *Mux) distribute(event Event) {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	for _, w := range m.watchers {
+		w.result <- event
+	}
+}
+
+// muxWatcher handles a single watcher of a mux
+type muxWatcher struct {
+	result chan Event
+	id     int64
+	m      *Mux
+}
+
+// ResultChan returns a channel to use for waiting on events.
+func (mw *muxWatcher) ResultChan() <-chan Event {
+	return mw.result
+}
+
+// Stop stops watching and removes mw from its list.
+func (mw *muxWatcher) Stop() {
+	mw.m.stopWatching(mw.id)
+}

pkg/watch/mux_test.go

@@ -0,0 +1,90 @@
+/*
+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 watch
+
+import (
+	"reflect"
+	"sync"
+	"testing"
+)
+
+func TestMux(t *testing.T) {
+	type myType struct {
+		ID    string
+		Value string
+	}
+	table := []Event{
+		{Added, myType{"foo", "hello world 1"}},
+		{Added, myType{"bar", "hello world 2"}},
+		{Modified, myType{"foo", "goodbye world 3"}},
+		{Deleted, myType{"bar", "hello world 4"}},
+	}
+
+	// The mux we're testing
+	m := NewMux(0)
+
+	// Add a bunch of watchers
+	const testWatchers = 2
+	wg := sync.WaitGroup{}
+	wg.Add(testWatchers)
+	for i := 0; i < testWatchers; i++ {
+		// Verify that each watcher gets the events in the correct order
+		go func(watcher int, w Interface) {
+			tableLine := 0
+			for {
+				event, ok := <-w.ResultChan()
+				if !ok {
+					break
+				}
+				if e, a := table[tableLine], event; !reflect.DeepEqual(e, a) {
+					t.Errorf("Watcher %v, line %v: Expected (%v, %#v), got (%v, %#v)",
+						watcher, tableLine, e.Type, e.Object, a.Type, a.Object)
+				} else {
+					t.Logf("Got (%v, %#v)", event.Type, event.Object)
+				}
+				tableLine++
+			}
+			wg.Done()
+		}(i, m.Watch())
+	}
+
+	for i, item := range table {
+		t.Logf("Sending %v", i)
+		m.Action(item.Type, item.Object)
+	}
+
+	m.Shutdown()
+
+	wg.Wait()
+}
+
+func TestMuxWatcherClose(t *testing.T) {
+	m := NewMux(0)
+	w := m.Watch()
+	w2 := m.Watch()
+	w.Stop()
+	m.Shutdown()
+	if _, open := <-w.ResultChan(); open {
+		t.Errorf("Stop didn't work?")
+	}
+	if _, open := <-w2.ResultChan(); open {
+		t.Errorf("Shutdown didn't work?")
+	}
+	// Extra stops don't hurt things
+	w.Stop()
+	w2.Stop()
+}