slog: internal/buffer

The internal/buffer package provides a pool-allocated byte buffer.

Change-Id: I85da789afbb93ca78ac8b0387f4bf0fc16663faf
Reviewed-on: https://go-review.googlesource.com/c/exp/+/426022
Reviewed-by: Alan Donovan <[email protected]>
Run-TryBot: Jonathan Amsterdam <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: jba

slog/internal/buffer/buffer.go

@@ -0,0 +1,45 @@
+// Copyright 2022 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.
+
+// Package buffer provides a pool-allocated byte buffer.
+package buffer
+
+import (
+	"sync"
+)
+
+// buffer adapted from go/src/fmt/print.go
+type Buffer []byte
+
+// Having an initial size gives a dramatic speedup.
+var bufPool = sync.Pool{
+	New: func() any {
+		b := make([]byte, 0, 1024)
+		return (*Buffer)(&b)
+	},
+}
+
+func New() *Buffer {
+	return bufPool.Get().(*Buffer)
+}
+
+func (b *Buffer) Free() {
+	// To reduce peak allocation, return only smaller buffers to the pool.
+	const maxBufferSize = 16 << 10
+	if cap(*b) <= maxBufferSize {
+		*b = (*b)[:0]
+		bufPool.Put(b)
+	}
+}
+func (b *Buffer) Write(p []byte) {
+	*b = append(*b, p...)
+}
+
+func (b *Buffer) WriteString(s string) {
+	*b = append(*b, s...)
+}
+
+func (b *Buffer) WriteByte(c byte) {
+	*b = append(*b, c)
+}

slog/internal/buffer/buffer_test.go

@@ -0,0 +1,31 @@
+// Copyright 2022 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.
+
+package buffer
+
+import "testing"
+
+func Test(t *testing.T) {
+	b := New()
+	defer b.Free()
+	b.WriteString("hello")
+	b.WriteByte(',')
+	b.Write([]byte(" world"))
+	got := string(*b)
+	want := "hello, world"
+	if got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}
+
+func TestAlloc(t *testing.T) {
+	got := int(testing.AllocsPerRun(5, func() {
+		b := New()
+		defer b.Free()
+		b.WriteString("not 1K worth of bytes")
+	}))
+	if got != 0 {
+		t.Errorf("got %d allocs, want 0", got)
+	}
+}