Skip cached updater singleflight result

We don't want to re-apply the previous singleflighted update.
Temporarily copying singleflight here until we add in behavior to the
golang package: golang/groupcache#61

go/updater/singleflight.go

@@ -0,0 +1,66 @@
+/*
+Copyright 2012 Google Inc.
+
+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.
+*/
+
+// This is a copy of https://github.com/golang/groupcache with a minor change
+// being discussed here: https://github.com/golang/groupcache/issues/61
+// This is temporary!
+
+package updater
+
+import "sync"
+
+// call is an in-flight or completed Do call
+type call struct {
+	wg  sync.WaitGroup
+	val interface{}
+	err error
+}
+
+// Group represents a class of work and forms a namespace in which
+// units of work can be executed with duplicate suppression.
+type Group struct {
+	mu 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.
+func (g *Group) Do(key string, fn func() (interface{}, error)) (interface{}, bool, error) {
+	g.mu.Lock()
+	if g.m == nil {
+		g.m = make(map[string]*call)
+	}
+	if c, ok := g.m[key]; ok {
+		g.mu.Unlock()
+		c.wg.Wait()
+		return c.val, true, c.err
+	}
+	c := new(call)
+	c.wg.Add(1)
+	g.m[key] = c
+	g.mu.Unlock()
+
+	c.val, c.err = fn()
+	c.wg.Done()
+
+	g.mu.Lock()
+	delete(g.m, key)
+	g.mu.Unlock()
+
+	return c.val, false, c.err
+}

go/updater/updater.go

@@ -16,7 +16,6 @@ import (
 	"time"
 
 	"github.com/blang/semver"
-	"github.com/golang/groupcache/singleflight"
 	"github.com/keybase/client/go/libkb"
 	"github.com/keybase/client/go/logger"
 	keybase1 "github.com/keybase/client/go/protocol"
@@ -30,7 +29,7 @@ type Updater struct {
 	source    sources.UpdateSource
 	config    Config
 	log       logger.Logger
-	callGroup singleflight.Group
+	callGroup Group
 }
 
 type UI interface {
@@ -351,7 +350,12 @@ func (u *Updater) Update(ui UI, force bool, requested bool) (*keybase1.Update, e
 	do := func() (interface{}, error) {
 		return u.update(ui, force, requested)
 	}
-	any, err := u.callGroup.Do("update", do)
+	any, cached, err := u.callGroup.Do("update", do)
+
+	if cached {
+		u.log.Info("Update call was singleflighted and returned cached result, skipping")
+		return nil, nil
+	}
 
 	update, ok := any.(*keybase1.Update)
 	if !ok {