mirror of https://github.com/golang/go.git
net/http: re-simplify HTTP/1.x status line writing
It used to be simple, and then it got complicated for speed (to reduce allocations, mostly), but that involved a mutex and hurt multi-core performance, contending on the mutex. A change was sent to try to improve that mutex contention in https://go-review.googlesource.com/c/42110/2/src/net/http/server.go but that introduced its own allocations (the string->interface{} boxing for the sync.Map key), which runs counter to the whole point of that statusLine function: to remove allocations. Instead, make the code simple again and not have a mutex. It's a bit slower for the single-core case, but nobody with a single-user HTTP server cares about 50 nanoseconds: name old time/op new time/op delta ResponseStatusLine 37.5ns ± 2% 87.1ns ± 2% +132.42% (p=0.029 n=4+4) ResponseStatusLine-2 63.1ns ± 1% 43.1ns ±12% -31.67% (p=0.029 n=4+4) ResponseStatusLine-4 53.8ns ± 8% 40.2ns ± 2% -25.29% (p=0.029 n=4+4) name old alloc/op new alloc/op delta ResponseStatusLine 0.00B ±NaN% 0.00B ±NaN% ~ (all samples are equal) ResponseStatusLine-2 0.00B ±NaN% 0.00B ±NaN% ~ (all samples are equal) ResponseStatusLine-4 0.00B ±NaN% 0.00B ±NaN% ~ (all samples are equal) name old allocs/op new allocs/op delta ResponseStatusLine 0.00 ±NaN% 0.00 ±NaN% ~ (all samples are equal) ResponseStatusLine-2 0.00 ±NaN% 0.00 ±NaN% ~ (all samples are equal) ResponseStatusLine-4 0.00 ±NaN% 0.00 ±NaN% ~ (all samples are equal) (Note the code could be even simpler with fmt.Fprintf, but that is relatively slow and involves a bunch of allocations getting arguments into interface{} for the call) Change-Id: I1fa119132dbbf97a8e7204ce3e0707d433060da2 Reviewed-on: https://go-review.googlesource.com/42133 Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Bryan Mills <bcmills@google.com>
This commit is contained in:
Brad Fitzpatrick
parent
16b6bb88eb
commit
07a22bbc11
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@ -17,17 +17,19 @@ import (
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)
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var (
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DefaultUserAgent = defaultUserAgent
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NewLoggingConn = newLoggingConn
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ExportAppendTime = appendTime
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ExportRefererForURL = refererForURL
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ExportServerNewConn = (*Server).newConn
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ExportCloseWriteAndWait = (*conn).closeWriteAndWait
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ExportErrRequestCanceled = errRequestCanceled
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ExportErrRequestCanceledConn = errRequestCanceledConn
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ExportServeFile = serveFile
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ExportScanETag = scanETag
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ExportHttp2ConfigureServer = http2ConfigureServer
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DefaultUserAgent = defaultUserAgent
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NewLoggingConn = newLoggingConn
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ExportAppendTime = appendTime
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ExportRefererForURL = refererForURL
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ExportServerNewConn = (*Server).newConn
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ExportCloseWriteAndWait = (*conn).closeWriteAndWait
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ExportErrRequestCanceled = errRequestCanceled
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ExportErrRequestCanceledConn = errRequestCanceledConn
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ExportServeFile = serveFile
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ExportScanETag = scanETag
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ExportHttp2ConfigureServer = http2ConfigureServer
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Export_shouldCopyHeaderOnRedirect = shouldCopyHeaderOnRedirect
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Export_writeStatusLine = writeStatusLine
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)
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func init() {
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@ -188,8 +190,6 @@ func ExportHttp2ConfigureTransport(t *Transport) error {
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return nil
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}
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var Export_shouldCopyHeaderOnRedirect = shouldCopyHeaderOnRedirect
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func (s *Server) ExportAllConnsIdle() bool {
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s.mu.Lock()
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defer s.mu.Unlock()
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@ -5539,3 +5539,14 @@ func TestServerValidatesMethod(t *testing.T) {
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}
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}
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}
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func BenchmarkResponseStatusLine(b *testing.B) {
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b.ReportAllocs()
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b.RunParallel(func(pb *testing.PB) {
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bw := bufio.NewWriter(ioutil.Discard)
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var buf3 [3]byte
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for pb.Next() {
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Export_writeStatusLine(bw, true, 200, buf3[:])
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}
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})
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}
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@ -439,9 +439,10 @@ type response struct {
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handlerDone atomicBool // set true when the handler exits
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// Buffers for Date and Content-Length
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dateBuf [len(TimeFormat)]byte
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clenBuf [10]byte
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// Buffers for Date, Content-Length, and status code
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dateBuf [len(TimeFormat)]byte
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clenBuf [10]byte
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statusBuf [3]byte
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// closeNotifyCh is the channel returned by CloseNotify.
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// TODO(bradfitz): this is currently (for Go 1.8) always
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@ -1379,7 +1380,7 @@ func (cw *chunkWriter) writeHeader(p []byte) {
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}
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}
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w.conn.bufw.WriteString(statusLine(w.req, code))
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writeStatusLine(w.conn.bufw, w.req.ProtoAtLeast(1, 1), code, w.statusBuf[:])
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cw.header.WriteSubset(w.conn.bufw, excludeHeader)
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setHeader.Write(w.conn.bufw)
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w.conn.bufw.Write(crlf)
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@ -1403,49 +1404,25 @@ func foreachHeaderElement(v string, fn func(string)) {
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}
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}
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// statusLines is a cache of Status-Line strings, keyed by code (for
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// HTTP/1.1) or negative code (for HTTP/1.0). This is faster than a
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// map keyed by struct of two fields. This map's max size is bounded
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// by 2*len(statusText), two protocol types for each known official
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// status code in the statusText map.
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var (
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statusMu sync.RWMutex
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statusLines = make(map[int]string)
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)
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// statusLine returns a response Status-Line (RFC 2616 Section 6.1)
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// for the given request and response status code.
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func statusLine(req *Request, code int) string {
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// Fast path:
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key := code
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proto11 := req.ProtoAtLeast(1, 1)
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if !proto11 {
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key = -key
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// writeStatusLine writes an HTTP/1.x Status-Line (RFC 2616 Section 6.1)
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// to bw. is11 is whether the HTTP request is HTTP/1.1. false means HTTP/1.0.
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// code is the response status code.
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// scratch is an optional scratch buffer. If it has at least capacity 3, it's used.
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func writeStatusLine(bw *bufio.Writer, is11 bool, code int, scratch []byte) {
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if is11 {
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bw.WriteString("HTTP/1.1 ")
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} else {
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bw.WriteString("HTTP/1.0 ")
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}
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statusMu.RLock()
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line, ok := statusLines[key]
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statusMu.RUnlock()
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if ok {
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return line
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if text, ok := statusText[code]; ok {
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bw.Write(strconv.AppendInt(scratch[:0], int64(code), 10))
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bw.WriteByte(' ')
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bw.WriteString(text)
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bw.WriteString("\r\n")
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} else {
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// don't worry about performance
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fmt.Fprintf(bw, "%03d status code %d\r\n", code, code)
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}
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// Slow path:
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proto := "HTTP/1.0"
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if proto11 {
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proto = "HTTP/1.1"
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}
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codestring := fmt.Sprintf("%03d", code)
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text, ok := statusText[code]
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if !ok {
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text = "status code " + codestring
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}
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line = proto + " " + codestring + " " + text + "\r\n"
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if ok {
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statusMu.Lock()
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defer statusMu.Unlock()
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statusLines[key] = line
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}
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return line
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}
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// bodyAllowed reports whether a Write is allowed for this response type.
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