Add bufferpool, a sync.Pool-backed pool of buffers

common/sync/bufferpool/buffer_pool_test.go

Index: common/sync/bufferpool/buffer_pool_test.go
diff --git a/common/sync/bufferpool/buffer_pool_test.go b/common/sync/bufferpool/buffer_pool_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..36f4e622b0e10b6d18a18a2dfec8f203547ebdf3
--- /dev/null
+++ b/common/sync/bufferpool/buffer_pool_test.go
@@ -0,0 +1,80 @@
+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package bufferpool
+
+import (
+	"fmt"
+	"testing"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestBufferPool(t *testing.T) {
+	t.Parallel()
+
+	Convey(`Testing P, the buffer pool`, t, func() {
+		var p P
+
+		Convey(`Basic functionality`, func() {
+			buf1 := p.Get()
+			buf1.WriteString("foo")
+			So(buf1.String(), ShouldEqual, "foo")
+
+			clone1 := buf1.Clone()
+			So(clone1, ShouldResemble, []byte("foo"))
+			buf1.Release()
+
+			buf2 := p.Get()
+			buf2.WriteString("bar")
+
+			// clone1 should still resemble "foo".
+			So(clone1, ShouldResemble, []byte("foo"))
+		})
+
+		Convey(`Double release panicks`, func() {
+			buf := p.Get()
+			buf.Release()
+			So(buf.Release, ShouldPanic)
+		})
+
+		Convey(`Concurrent access`, func() {
+			const goroutines = 16
+			const rounds = 128
+
+			startC := make(chan struct{})
+			doneC := make(chan []byte)
+
+			for i := 0; i < goroutines; i++ {
+				go func(idx int) {
+					<-startC
+
+					for j := 0; j < rounds; j++ {
+						buf := p.Get()
+						fmt.Fprintf(buf, "%d.%d", idx, j)
+						doneC <- buf.Clone()
+						buf.Release()
+					}
+				}(i)
+			}
+
+			// Collect all of our data. Store it as bytes so that if there is
+			// conflict / reuse, something will hopefully go wrong.
+			close(startC)
+			data := make([][]byte, 0, goroutines*rounds)
+			for i := 0; i < goroutines; i++ {
+				for j := 0; j < rounds; j++ {
+					data = append(data, <-doneC)
+				}
+			}
+
+			// Assert that it all exists.
+			sorted := make(map[string]struct{}, len(data))
+			for _, d := range data {
+				sorted[string(d)] = struct{}{}
+			}
+			So(len(sorted), ShouldEqual, goroutines*rounds)
+		})
+	})
+}