Add runner utility.

pkg/util/runner.go

+/*
+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 util
+
+import (
+	"sync"
+)
+
+// Runner is an abstraction to make it easy to start and stop groups of things that can be
+// described by a single function which waits on a channel close to exit.
+type Runner struct {
+	lock      sync.Mutex
+	loopFuncs []func(stop chan struct{})
+	stop      *chan struct{}
+}
+
+// NewRunner makes a runner for the given function(s). The function(s) should loop until
+// the channel is closed.
+func NewRunner(f ...func(stop chan struct{})) *Runner {
+	return &Runner{loopFuncs: f}
+}
+
+// Start begins running.
+func (r *Runner) Start() {
+	r.lock.Lock()
+	defer r.lock.Unlock()
+	if r.stop == nil {
+		c := make(chan struct{})
+		r.stop = &c
+		for i := range r.loopFuncs {
+			go r.loopFuncs[i](*r.stop)
+		}
+	}
+}
+
+// Stop stops running.
+func (r *Runner) Stop() {
+	r.lock.Lock()
+	defer r.lock.Unlock()
+	if r.stop != nil {
+		close(*r.stop)
+		r.stop = nil
+	}
+}

pkg/util/runner_test.go

+/*
+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 util
+
+import (
+	"fmt"
+	"sync"
+	"testing"
+)
+
+func TestRunner(t *testing.T) {
+	var (
+		lock   sync.Mutex
+		events []string
+		funcs  []func(chan struct{})
+	)
+	done := make(chan struct{}, 20)
+	for i := 0; i < 10; i++ {
+		iCopy := i
+		funcs = append(funcs, func(c chan struct{}) {
+			lock.Lock()
+			events = append(events, fmt.Sprintf("%v starting\n", iCopy))
+			lock.Unlock()
+			<-c
+			lock.Lock()
+			events = append(events, fmt.Sprintf("%v stopping\n", iCopy))
+			lock.Unlock()
+			done <- struct{}{}
+		})
+	}
+
+	r := NewRunner(funcs...)
+	r.Start()
+	r.Stop()
+	for i := 0; i < 10; i++ {
+		<-done
+	}
+	if len(events) != 20 {
+		t.Errorf("expected 20 events, but got:\n%v\n", events)
+	}
+}