Vendor dependencies for GCS

vendor/cloud.google.com/go/internal/atomiccache/atomiccache.go

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+// Copyright 2016 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 atomiccache provides a map-based cache that supports very fast
+// reads.
+package atomiccache
+
+import (
+	"sync"
+	"sync/atomic"
+)
+
+type mapType map[interface{}]interface{}
+
+// Cache is a map-based cache that supports fast reads via use of atomics.
+// Writes are slow, requiring a copy of the entire cache.
+// The zero Cache is an empty cache, ready for use.
+type Cache struct {
+	val atomic.Value // mapType
+	mu  sync.Mutex   // used only by writers
+}
+
+// Get returns the value of the cache at key. If there is no value,
+// getter is called to provide one, and the cache is updated.
+// The getter function may be called concurrently. It should be pure,
+// returning the same value for every call.
+func (c *Cache) Get(key interface{}, getter func() interface{}) interface{} {
+	mp, _ := c.val.Load().(mapType)
+	if v, ok := mp[key]; ok {
+		return v
+	}
+
+	// Compute value without lock.
+	// Might duplicate effort but won't hold other computations back.
+	newV := getter()
+
+	c.mu.Lock()
+	mp, _ = c.val.Load().(mapType)
+	newM := make(mapType, len(mp)+1)
+	for k, v := range mp {
+		newM[k] = v
+	}
+	newM[key] = newV
+	c.val.Store(newM)
+	c.mu.Unlock()
+	return newV
+}

vendor/cloud.google.com/go/internal/atomiccache/atomiccache_test.go

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+// Copyright 2016 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 atomiccache
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestGet(t *testing.T) {
+	var c Cache
+	called := false
+	get := func(k interface{}) interface{} {
+		return c.Get(k, func() interface{} {
+			called = true
+			return fmt.Sprintf("v%d", k)
+		})
+	}
+	got := get(1)
+	if want := "v1"; got != want {
+		t.Errorf("got %v, want %v", got, want)
+	}
+	if !called {
+		t.Error("getter not called, expected a call")
+	}
+	called = false
+	got = get(1)
+	if want := "v1"; got != want {
+		t.Errorf("got %v, want %v", got, want)
+	}
+	if called {
+		t.Error("getter unexpectedly called")
+	}
+}