go 50 lines · 8 steps

Pooling buffers for logfmt encoding in Go

A sync.Pool recycles byte buffers so each log record is built without fresh allocations.

Explained by highlit
Intermediate object-pooling memory-reuse serialization io
1package logfmt
2 
3import (
4 "bytes"
5 "io"
6 "sync"
7)
8 
9var bufferPool = sync.Pool{
10 New: func() any {
11 return new(bytes.Buffer)
12 },
13}
14 
15func getBuffer() *bytes.Buffer {
16 return bufferPool.Get().(*bytes.Buffer)
17}
18 
19func putBuffer(buf *bytes.Buffer) {
20 if buf.Cap() > 64<<10 {
21 return
22 }
23 buf.Reset()
24 bufferPool.Put(buf)
25}
26 
27func WriteRecord(w io.Writer, fields map[string]string) (int, error) {
28 buf := getBuffer()
29 defer putBuffer(buf)
30 
31 first := true
32 for key, value := range fields {
33 if !first {
34 buf.WriteByte(' ')
35 }
36 first = false
37 buf.WriteString(key)
38 buf.WriteByte('=')
39 if bytes.ContainsAny([]byte(value), " \"") {
40 buf.WriteByte('"')
41 buf.WriteString(value)
42 buf.WriteByte('"')
43 } else {
44 buf.WriteString(value)
45 }
46 }
47 buf.WriteByte('\n')
48 
49 return w.Write(buf.Bytes())
50}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1A sync.Pool amortizes allocation cost by reusing temporary objects across calls.
  2. 2Capping the size of returned objects prevents the pool from hoarding oversized buffers.
  3. 3Always reset pooled objects before returning them so stale data never leaks into the next user.

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