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bufio: reuse Writer buffers after Flush

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A bufio.Writer.Flush marks the usual end of a Writer's
life. Recycle its internal buffer on those explicit flushes,
but not on normal, as-needed internal flushes.

benchmark               old ns/op    new ns/op    delta
BenchmarkWriterEmpty         1959          727  -62.89%

benchmark              old allocs   new allocs    delta
BenchmarkWriterEmpty            2            1  -50.00%

benchmark               old bytes    new bytes    delta
BenchmarkWriterEmpty         4215           83  -98.03%

R=gri, iant
CC=gobot, golang-dev, voidlogic7
https://golang.org/cl/9459044
This commit is contained in:
Brad Fitzpatrick 2013-05-21 15:51:49 -07:00
parent ddda7980c5
commit 99f6722860
2 changed files with 89 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

78
src/pkg/bufio/bufio.go
View File

@ -29,7 +29,7 @@ var (
// Reader implements buffering for an io.Reader object.
type Reader struct {
buf []byte // either nil or []byte of size bufSize
buf []byte // either nil or []byte of length bufSize
bufSize int
rd io.Reader
r, w int
@ -314,7 +314,7 @@ func (b *Reader) ReadSlice(delim byte) (line []byte, err error) {
}
// Buffer is full?
if b.Buffered() >= len(b.buf) {
if b.Buffered() >= b.bufSize {
b.r = b.w
return b.buf, ErrBufferFull
}
@ -473,10 +473,11 @@ func (b *Reader) writeBuf(w io.Writer) (int64, error) {
// If an error occurs writing to a Writer, no more data will be
// accepted and all subsequent writes will return the error.
type Writer struct {
err error
buf []byte
n int
wr io.Writer
err error
buf []byte // either nil or []byte of length bufSize
bufSize int
n int
wr io.Writer
}
// NewWriterSize returns a new Writer whose buffer has at least the specified
@ -485,16 +486,20 @@ type Writer struct {
func NewWriterSize(wr io.Writer, size int) *Writer {
// Is it already a Writer?
b, ok := wr.(*Writer)
if ok && len(b.buf) >= size {
if ok && b.bufSize >= size {
return b
}
if size <= 0 {
size = defaultBufSize
}
b = new(Writer)
// TODO(bradfitz): make Writer buffers lazy too, like Reader's
b.buf = make([]byte, size)
b.wr = wr
b = &Writer{
wr: wr,
bufSize: size,
}
if size > defaultBufSize {
// TODO(bradfitz): make all buffer sizes recycle
b.buf = make([]byte, b.bufSize)
}
return b
}
@ -503,8 +508,38 @@ func NewWriter(wr io.Writer) *Writer {
return NewWriterSize(wr, defaultBufSize)
}
// allocBuf makes b.buf non-nil.
func (b *Writer) allocBuf() {
if b.buf != nil {
return
}
select {
case b.buf = <-bufCache:
b.buf = b.buf[:b.bufSize]
default:
b.buf = make([]byte, b.bufSize, defaultBufSize)
}
}
// putBuf returns b.buf if it's unused.
func (b *Writer) putBuf() {
if b.n == 0 && cap(b.buf) == defaultBufSize {
select {
case bufCache <- b.buf:
b.buf = nil
default:
}
}
}
// Flush writes any buffered data to the underlying io.Writer.
func (b *Writer) Flush() error {
err := b.flush()
b.putBuf()
return err
}
func (b *Writer) flush() error {
if b.err != nil {
return b.err
}
@ -528,7 +563,7 @@ func (b *Writer) Flush() error {
}
// Available returns how many bytes are unused in the buffer.
func (b *Writer) Available() int { return len(b.buf) - b.n }
func (b *Writer) Available() int { return b.bufSize - b.n }
// Buffered returns the number of bytes that have been written into the current buffer.
func (b *Writer) Buffered() int { return b.n }
@ -538,6 +573,7 @@ func (b *Writer) Buffered() int { return b.n }
// If nn < len(p), it also returns an error explaining
// why the write is short.
func (b *Writer) Write(p []byte) (nn int, err error) {
b.allocBuf()
for len(p) > b.Available() && b.err == nil {
var n int
if b.Buffered() == 0 {
@ -547,7 +583,7 @@ func (b *Writer) Write(p []byte) (nn int, err error) {
} else {
n = copy(b.buf[b.n:], p)
b.n += n
b.Flush()
b.flush()
}
nn += n
p = p[n:]
@ -566,9 +602,12 @@ func (b *Writer) WriteByte(c byte) error {
if b.err != nil {
return b.err
}
if b.Available() <= 0 && b.Flush() != nil {
if b.Available() <= 0 && b.flush() != nil {
return b.err
}
if b.buf == nil {
b.allocBuf()
}
b.buf[b.n] = c
b.n++
return nil
@ -577,6 +616,9 @@ func (b *Writer) WriteByte(c byte) error {
// WriteRune writes a single Unicode code point, returning
// the number of bytes written and any error.
func (b *Writer) WriteRune(r rune) (size int, err error) {
if b.buf == nil {
b.allocBuf()
}
if r < utf8.RuneSelf {
err = b.WriteByte(byte(r))
if err != nil {
@ -589,7 +631,7 @@ func (b *Writer) WriteRune(r rune) (size int, err error) {
}
n := b.Available()
if n < utf8.UTFMax {
if b.Flush(); b.err != nil {
if b.flush(); b.err != nil {
return 0, b.err
}
n = b.Available()
@ -608,13 +650,14 @@ func (b *Writer) WriteRune(r rune) (size int, err error) {
// If the count is less than len(s), it also returns an error explaining
// why the write is short.
func (b *Writer) WriteString(s string) (int, error) {
b.allocBuf()
nn := 0
for len(s) > b.Available() && b.err == nil {
n := copy(b.buf[b.n:], s)
b.n += n
nn += n
s = s[n:]
b.Flush()
b.flush()
}
if b.err != nil {
return nn, b.err
@ -627,6 +670,7 @@ func (b *Writer) WriteString(s string) (int, error) {
// ReadFrom implements io.ReaderFrom.
func (b *Writer) ReadFrom(r io.Reader) (n int64, err error) {
b.allocBuf()
if b.Buffered() == 0 {
if w, ok := b.wr.(io.ReaderFrom); ok {
return w.ReadFrom(r)
@ -641,7 +685,7 @@ func (b *Writer) ReadFrom(r io.Reader) (n int64, err error) {
b.n += m
n += int64(m)
if b.Available() == 0 {
if err1 := b.Flush(); err1 != nil {
if err1 := b.flush(); err1 != nil {
return n, err1
}
}

28
src/pkg/bufio/bufio_test.go
View File

@ -1098,3 +1098,31 @@ func BenchmarkReaderEmpty(b *testing.B) {
}
}
}
func BenchmarkWriterEmpty(b *testing.B) {
b.ReportAllocs()
str := strings.Repeat("x", 1<<10)
bs := []byte(str)
for i := 0; i < b.N; i++ {
bw := NewWriter(ioutil.Discard)
bw.Flush()
bw.WriteByte('a')
bw.Flush()
bw.WriteRune('B')
bw.Flush()
bw.Write(bs)
bw.Flush()
bw.WriteString(str)
bw.Flush()
}
}
func BenchmarkWriterFlush(b *testing.B) {
b.ReportAllocs()
bw := NewWriter(ioutil.Discard)
str := strings.Repeat("x", 50)
for i := 0; i < b.N; i++ {
bw.WriteString(str)
bw.Flush()
}
}