reset items from sync.pool

[komuw]

we should reset whatever we get from sync.pool b4 use;

meli/image.go

Line 118 in 9e036d4

bufp := blackHolePool.Get().(*[]byte)

[komuw]

if you run the following code:

func BenchmarkPoolReadFrom(b *testing.B) {
	r := strings.NewReader("hello")
	b.ResetTimer()
	for n := 0; n < 3; n++ {
		_, _ = poolReadFrom(r)
	}
}

and inside

meli/image.go

Line 118 in 9e036d4

bufp := blackHolePool.Get().(*[]byte)

you;

fmt.Printf("#%+v", bufp)

you get an output like;

#&[0 0 0 0 0 0 0 0]

#&[104 101 108 108 111 0 0 0]

#&[104 101 108 108 111 0 0 0]

#&[0 0 0 0 0 0 0 0]

#&[104 101 108 108 111 0 0 0]

So the first time we get a []byte from sync.Pool it is zeroed, but after that every other access may already have data in it.
also

fmt.Printf("#%+v", string(*bufp))

prints;

#
#hello
#hello
#

get 1 & 4 are okay(zeroed) but get 2 & 3 are not.

[komuw]

package main

import (
	"bytes"
	"fmt"
	"io"
	"strings"
	"sync"
)

const max = 512

var blackHolePool = sync.Pool{
	New: func() interface{} {
		return make([]byte, max)
	},
}

func main() {
	x := []string{"hello", "cool", "three", "four"}
	for _, v := range x {
		src := strings.NewReader(v)
		bufp := blackHolePool.Get().([]byte)
		dst := bytes.NewBuffer(bufp)
		io.Copy(dst, src)

		blackHolePool.Put(bufp[:max])

		fmt.Println(dst)
	}

}

[komuw]

see: golang/go#27740