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godoc: added systematic throttling to indexing goroutine
- implemented stand-alone Throttle mechanism - added new flag -index_throttle to godoc - index throttling enables index creation when running godoc on app engine as it keeps godoc responsive R=rsc, dsymonds, adg CC=golang-dev https://golang.org/cl/4963043
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@ -18,6 +18,7 @@ GOFILES=\
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parser.go\
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snippet.go\
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spec.go\
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throttle.go\
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utils.go\
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zip.go\
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@ -50,6 +50,11 @@ The flags are:
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-index
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enable identifier and full text search index
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(no search box is shown if -index is not set)
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-index_throttle=0.75
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index throttle value; a value of 0 means no time is allocated
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to the indexer (the indexer will never finish), a value of 1.0
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means that index creation is running at full throttle (other
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goroutines may get no time while the index is built)
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-maxresults=10000
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maximum number of full text search results shown
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(no full text index is built if maxresults <= 0)
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@ -63,8 +63,9 @@ var (
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templateDir = flag.String("templates", "", "directory containing alternate template files")
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// search index
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indexEnabled = flag.Bool("index", false, "enable search index")
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maxResults = flag.Int("maxresults", 10000, "maximum number of full text search results shown")
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indexEnabled = flag.Bool("index", false, "enable search index")
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maxResults = flag.Int("maxresults", 10000, "maximum number of full text search results shown")
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indexThrottle = flag.Float64("index_throttle", 0.75, "index throttle value; 0.0 = no time allocated, 1.0 = full throttle")
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// file system mapping
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fs FileSystem // the underlying file system for godoc
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@ -1148,7 +1149,7 @@ func indexer() {
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log.Printf("updating index...")
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}
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start := time.Nanoseconds()
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index := NewIndex(fsDirnames(), *maxResults > 0)
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index := NewIndex(fsDirnames(), *maxResults > 0, *indexThrottle)
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stop := time.Nanoseconds()
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searchIndex.set(index)
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if *verbose {
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@ -736,8 +736,9 @@ func canonical(w string) string { return strings.ToLower(w) }
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// NewIndex creates a new index for the .go files
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// in the directories given by dirnames.
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//
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func NewIndex(dirnames <-chan string, fulltextIndex bool) *Index {
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func NewIndex(dirnames <-chan string, fulltextIndex bool, throttle float64) *Index {
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var x Indexer
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th := NewThrottle(throttle, 0.1e9) // run at least 0.1s at a time
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// initialize Indexer
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x.fset = token.NewFileSet()
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@ -753,6 +754,7 @@ func NewIndex(dirnames <-chan string, fulltextIndex bool) *Index {
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if !f.IsDirectory() {
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x.visitFile(dirname, f, fulltextIndex)
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}
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th.Throttle()
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}
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}
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@ -778,6 +780,7 @@ func NewIndex(dirnames <-chan string, fulltextIndex bool) *Index {
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Others: others,
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}
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wlist = append(wlist, &wordPair{canonical(w), w})
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th.Throttle()
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}
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x.stats.Words = len(words)
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88
src/cmd/godoc/throttle.go
Normal file
88
src/cmd/godoc/throttle.go
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@ -0,0 +1,88 @@
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import "time"
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// A Throttle permits throttling of a goroutine by
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// calling the Throttle method repeatedly.
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//
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type Throttle struct {
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f float64 // f = (1-r)/r for 0 < r < 1
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tm int64 // minimum run time slice; >= 0
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tr int64 // accumulated time running
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ts int64 // accumulated time stopped
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tt int64 // earliest throttle time (= time Throttle returned + tm)
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}
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// NewThrottle creates a new Throttle with a throttle value r and
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// a minimum allocated run time slice of tm nanoseconds:
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//
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// r == 0: "empty" throttle; the goroutine is always sleeping
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// r == 1: full throttle; the goroutine is never sleeping
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//
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// A value of r == 0.6 throttles a goroutine such that it runs
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// approx. 60% of the time, and sleeps approx. 40% of the time.
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// Values of r < 0 or r > 1 are clamped down to values between 0 and 1.
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// Values of tm < 0 are set to 0.
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//
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func NewThrottle(r float64, tm int64) *Throttle {
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var f float64
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switch {
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case r <= 0:
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f = -1 // indicates always sleep
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case r >= 1:
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f = 0 // assume r == 1 (never sleep)
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default:
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// 0 < r < 1
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f = (1 - r) / r
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}
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if tm < 0 {
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tm = 0
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}
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return &Throttle{f: f, tm: tm, tt: time.Nanoseconds() + tm}
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}
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// Throttle calls time.Sleep such that over time the ratio tr/ts between
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// accumulated run (tr) and sleep times (ts) approximates the value 1/(1-r)
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// where r is the throttle value. Throttle returns immediately (w/o sleeping)
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// if less than tm ns have passed since the last call to Throttle.
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//
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func (p *Throttle) Throttle() {
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if p.f < 0 {
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select {} // always sleep
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}
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t0 := time.Nanoseconds()
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if t0 < p.tt {
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return // keep running (minimum time slice not exhausted yet)
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}
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// accumulate running time
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p.tr += t0 - (p.tt - p.tm)
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// compute sleep time
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// Over time we want:
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//
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// tr/ts = r/(1-r)
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//
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// Thus:
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//
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// ts = tr*f with f = (1-r)/r
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//
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// After some incremental run time δr added to the total run time
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// tr, the incremental sleep-time δs to get to the same ratio again
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// after waking up from time.Sleep is:
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if δs := int64(float64(p.tr)*p.f) - p.ts; δs > 0 {
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time.Sleep(δs)
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}
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// accumulate (actual) sleep time
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t1 := time.Nanoseconds()
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p.ts += t1 - t0
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// set earliest next throttle time
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p.tt = t1 + p.tm
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}
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