Switch from glide to dep. Check in vendor/

vendor/github.com/miekg/dns/singleinflight.go

@@ -0,0 +1,57 @@
+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Adapted for dns package usage by Miek Gieben.
+
+package dns
+
+import "sync"
+import "time"
+
+// call is an in-flight or completed singleflight.Do call
+type call struct {
+	wg   sync.WaitGroup
+	val  *Msg
+	rtt  time.Duration
+	err  error
+	dups int
+}
+
+// singleflight represents a class of work and forms a namespace in
+// which units of work can be executed with duplicate suppression.
+type singleflight struct {
+	sync.Mutex                  // protects m
+	m          map[string]*call // lazily initialized
+}
+
+// Do executes and returns the results of the given function, making
+// sure that only one execution is in-flight for a given key at a
+// time. If a duplicate comes in, the duplicate caller waits for the
+// original to complete and receives the same results.
+// The return value shared indicates whether v was given to multiple callers.
+func (g *singleflight) Do(key string, fn func() (*Msg, time.Duration, error)) (v *Msg, rtt time.Duration, err error, shared bool) {
+	g.Lock()
+	if g.m == nil {
+		g.m = make(map[string]*call)
+	}
+	if c, ok := g.m[key]; ok {
+		c.dups++
+		g.Unlock()
+		c.wg.Wait()
+		return c.val, c.rtt, c.err, true
+	}
+	c := new(call)
+	c.wg.Add(1)
+	g.m[key] = c
+	g.Unlock()
+
+	c.val, c.rtt, c.err = fn()
+	c.wg.Done()
+
+	g.Lock()
+	delete(g.m, key)
+	g.Unlock()
+
+	return c.val, c.rtt, c.err, c.dups > 0
+}