// but copied here to avoid the io.Discard optimization in Logger.
type discard struct{}

func (discard) Write(p []byte) (int, error) {
	return len(p), nil
}

func BenchmarkConcurrent(b *testing.B) {
	l := New(discard{}, "prefix: ", Ldate|Ltime|Lmicroseconds|Llongfile|Lmsgprefix)
	var group sync.WaitGroup
	for i := runtime.NumCPU(); i > 0; i-- {
		group.Add(1)
		go func() {