From 9dbcc5ae805ff5af66bdd30076456862408fded1 Mon Sep 17 00:00:00 2001
From: Vladimir Mihailenco <vladimir.webdev@gmail.com>
Date: Sat, 1 Jul 2017 12:51:06 +0300
Subject: [PATCH] Vendor syncutil.Once

---
 .travis.yml      |  1 -
 cluster.go       |  4 +---
 internal/once.go | 60 ++++++++++++++++++++++++++++++++++++++++++++++++
 ring.go          |  4 +---
 4 files changed, 62 insertions(+), 7 deletions(-)
 create mode 100644 internal/once.go

diff --git a/.travis.yml b/.travis.yml
index 7df76b9..f8e0d65 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,6 +16,5 @@ matrix:
     - go: tip
 
 install:
-  - go get go4.org/syncutil
   - go get github.com/onsi/ginkgo
   - go get github.com/onsi/gomega
diff --git a/cluster.go b/cluster.go
index 62dfe4a..f758b01 100644
--- a/cluster.go
+++ b/cluster.go
@@ -8,8 +8,6 @@ import (
 	"sync/atomic"
 	"time"
 
-	"go4.org/syncutil"
-
 	"github.com/go-redis/redis/internal"
 	"github.com/go-redis/redis/internal/hashtag"
 	"github.com/go-redis/redis/internal/pool"
@@ -347,7 +345,7 @@ type ClusterClient struct {
 	nodes  *clusterNodes
 	_state atomic.Value
 
-	cmdsInfoOnce syncutil.Once
+	cmdsInfoOnce internal.Once
 	cmdsInfo     map[string]*CommandInfo
 
 	// Reports where slots reloading is in progress.
diff --git a/internal/once.go b/internal/once.go
new file mode 100644
index 0000000..64f4627
--- /dev/null
+++ b/internal/once.go
@@ -0,0 +1,60 @@
+/*
+Copyright 2014 The Camlistore Authors
+
+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 internal
+
+import (
+	"sync"
+	"sync/atomic"
+)
+
+// A Once will perform a successful action exactly once.
+//
+// Unlike a sync.Once, this Once's func returns an error
+// and is re-armed on failure.
+type Once struct {
+	m    sync.Mutex
+	done uint32
+}
+
+// Do calls the function f if and only if Do has not been invoked
+// without error for this instance of Once.  In other words, given
+// 	var once Once
+// if once.Do(f) is called multiple times, only the first call will
+// invoke f, even if f has a different value in each invocation unless
+// f returns an error.  A new instance of Once is required for each
+// function to execute.
+//
+// Do is intended for initialization that must be run exactly once.  Since f
+// is niladic, it may be necessary to use a function literal to capture the
+// arguments to a function to be invoked by Do:
+// 	err := config.once.Do(func() error { return config.init(filename) })
+func (o *Once) Do(f func() error) error {
+	if atomic.LoadUint32(&o.done) == 1 {
+		return nil
+	}
+	// Slow-path.
+	o.m.Lock()
+	defer o.m.Unlock()
+	var err error
+	if o.done == 0 {
+		err = f()
+		if err == nil {
+			atomic.StoreUint32(&o.done, 1)
+		}
+	}
+	return err
+}
diff --git a/ring.go b/ring.go
index 5d94519..be92510 100644
--- a/ring.go
+++ b/ring.go
@@ -9,8 +9,6 @@ import (
 	"sync/atomic"
 	"time"
 
-	"go4.org/syncutil"
-
 	"github.com/go-redis/redis/internal"
 	"github.com/go-redis/redis/internal/consistenthash"
 	"github.com/go-redis/redis/internal/hashtag"
@@ -136,7 +134,7 @@ type Ring struct {
 	hash   *consistenthash.Map
 	shards map[string]*ringShard
 
-	cmdsInfoOnce syncutil.Once
+	cmdsInfoOnce internal.Once
 	cmdsInfo     map[string]*CommandInfo
 
 	closed bool