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bufio: in Reader.WriteTo, try to use target's ReaderFrom

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This is the simple half of https://golang.org/cl/53560043/ with
a new benchmark. pongad is in the C+A files already.

benchmark                         old ns/op     new ns/op     delta
BenchmarkReaderWriteToOptimal     2054          825           -59.83%

Update #6373

LGTM=iant, gri
R=golang-codereviews, iant, gri
CC=golang-codereviews
https://golang.org/cl/69220046
This commit is contained in:
Brad Fitzpatrick 2014-02-27 10:48:36 -08:00
parent 08706f19b4
commit b00e4770d9
2 changed files with 29 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
src/pkg/bufio/bufio.go
View File

@ -410,6 +410,12 @@ func (b *Reader) WriteTo(w io.Writer) (n int64, err error) {
return n, err
}
if w, ok := w.(io.ReaderFrom); ok {
m, err := w.ReadFrom(b.rd)
n += m
return n, err
}
for b.fill(); b.r < b.w; b.fill() {
m, err := b.writeBuf(w)
n += m

33
src/pkg/bufio/bufio_test.go
View File

@ -1094,20 +1094,12 @@ func TestWriterReset(t *testing.T) {
// An onlyReader only implements io.Reader, no matter what other methods the underlying implementation may have.
type onlyReader struct {
r io.Reader
}
func (r onlyReader) Read(b []byte) (int, error) {
return r.r.Read(b)
io.Reader
}
// An onlyWriter only implements io.Writer, no matter what other methods the underlying implementation may have.
type onlyWriter struct {
w io.Writer
}
func (w onlyWriter) Write(b []byte) (int, error) {
return w.w.Write(b)
io.Writer
}
func BenchmarkReaderCopyOptimal(b *testing.B) {
@ -1152,6 +1144,27 @@ func BenchmarkReaderCopyNoWriteTo(b *testing.B) {
}
}
func BenchmarkReaderWriteToOptimal(b *testing.B) {
const bufSize = 16 << 10
buf := make([]byte, bufSize)
r := bytes.NewReader(buf)
srcReader := NewReaderSize(onlyReader{r}, 1<<10)
if _, ok := ioutil.Discard.(io.ReaderFrom); !ok {
b.Fatal("ioutil.Discard doesn't support ReaderFrom")
}
for i := 0; i < b.N; i++ {
r.Seek(0, 0)
srcReader.Reset(onlyReader{r})
n, err := srcReader.WriteTo(ioutil.Discard)
if err != nil {
b.Fatal(err)
}
if n != bufSize {
b.Fatalf("n = %d; want %d", n, bufSize)
}
}
}
func BenchmarkWriterCopyOptimal(b *testing.B) {
// Optimal case is where the underlying writer implements io.ReaderFrom
srcBuf := bytes.NewBuffer(make([]byte, 8192))