net/http: server optimization; reduce GCs, generate ~half the garbage

There was another bufio.Writer not being reused, found with
GOGC=off and -test.memprofile.

benchmark                               old ns/op    new ns/op    delta
BenchmarkServerFakeConnWithKeepAlive        18270        16046  -12.17%

benchmark                              old allocs   new allocs    delta
BenchmarkServerFakeConnWithKeepAlive           38           36   -5.26%

benchmark                               old bytes    new bytes    delta
BenchmarkServerFakeConnWithKeepAlive         4598         2488  -45.89%

Update #5100

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/8038047

diff --git a/src/pkg/net/http/server.go b/src/pkg/net/http/server.go
index aee3229d37bef8a144cf557277fc11c6628345ef..8a325720a0e0b4da7624551598d1d982bd6a6266 100644 (file)
--- a/src/pkg/net/http/server.go
+++ b/src/pkg/net/http/server.go
@@ -281,6 +281,7 @@ type response struct {
 
        w  *bufio.Writer // buffers output in chunks to chunkWriter
        cw *chunkWriter
+       sw *switchWriter // of the bufio.Writer, for return to putBufioWriter
 
        // handlerHeader is the Header that Handlers get access to,
        // which may be retained and mutated even after WriteHeader.
@@ -381,7 +382,7 @@ func (srv *Server) newConn(rwc net.Conn) (c *conn, err error) {
        c.sr = liveSwitchReader{r: c.rwc}
        c.lr = io.LimitReader(&c.sr, noLimit).(*io.LimitedReader)
        br, sr := newBufioReader(c.lr)
-       bw, sw := newBufioWriter(c.rwc)
+       bw, sw := newBufioWriterSize(c.rwc, 4<<10)
        c.buf = bufio.NewReadWriter(br, bw)
        c.bufswr = sr
        c.bufsww = sw
@@ -402,10 +403,21 @@ type bufioWriterPair struct {
 
 // TODO: use a sync.Cache instead
 var (
-       bufioReaderCache = make(chan bufioReaderPair, 4)
-       bufioWriterCache = make(chan bufioWriterPair, 4)
+       bufioReaderCache   = make(chan bufioReaderPair, 4)
+       bufioWriterCache2k = make(chan bufioWriterPair, 4)
+       bufioWriterCache4k = make(chan bufioWriterPair, 4)
 )
 
+func bufioWriterCache(size int) chan bufioWriterPair {
+       switch size {
+       case 2 << 10:
+               return bufioWriterCache2k
+       case 4 << 10:
+               return bufioWriterCache4k
+       }
+       return nil
+}
+
 func newBufioReader(r io.Reader) (*bufio.Reader, *switchReader) {
        select {
        case p := <-bufioReaderCache:
@@ -429,14 +441,14 @@ func putBufioReader(br *bufio.Reader, sr *switchReader) {
        }
 }
 
-func newBufioWriter(w io.Writer) (*bufio.Writer, *switchWriter) {
+func newBufioWriterSize(w io.Writer, size int) (*bufio.Writer, *switchWriter) {
        select {
-       case p := <-bufioWriterCache:
+       case p := <-bufioWriterCache(size):
                p.sw.Writer = w
                return p.bw, p.sw
        default:
                sw := &switchWriter{w}
-               return bufio.NewWriter(sw), sw
+               return bufio.NewWriterSize(sw, size), sw
        }
 }
 
@@ -454,7 +466,7 @@ func putBufioWriter(bw *bufio.Writer, sw *switchWriter) {
        }
        sw.Writer = nil
        select {
-       case bufioWriterCache <- bufioWriterPair{bw, sw}:
+       case bufioWriterCache(bw.Available()) <- bufioWriterPair{bw, sw}:
        default:
        }
 }
@@ -540,7 +552,7 @@ func (c *conn) readRequest() (w *response, err error) {
                cw:            new(chunkWriter),
        }
        w.cw.res = w
-       w.w = bufio.NewWriterSize(w.cw, bufferBeforeChunkingSize)
+       w.w, w.sw = newBufioWriterSize(w.cw, bufferBeforeChunkingSize)
        return w, nil
 }
 
@@ -802,6 +814,7 @@ func (w *response) finishRequest() {
        }
 
        w.w.Flush()
+       putBufioWriter(w.w, w.sw)
        w.cw.close()
        w.conn.buf.Flush()