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https://github.com/golang/go
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212914f573
Make sure dequeueing from a channel queue does not exhibit quadratic time behavior. Change-Id: Ifb7c709b026f74c7e783610d4914dd92909a441b Reviewed-on: https://go-review.googlesource.com/1212 Reviewed-by: Russ Cox <rsc@golang.org>
95 lines
2.1 KiB
Go
95 lines
2.1 KiB
Go
// +build darwin linux
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// run
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// Copyright 2014 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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// Test that dequeueing from a pending channel doesn't
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// take linear time.
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package main
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import (
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"fmt"
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"runtime"
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"time"
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)
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// checkLinear asserts that the running time of f(n) is in O(n).
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// tries is the initial number of iterations.
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func checkLinear(typ string, tries int, f func(n int)) {
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// Depending on the machine and OS, this test might be too fast
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// to measure with accurate enough granularity. On failure,
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// make it run longer, hoping that the timing granularity
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// is eventually sufficient.
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timeF := func(n int) time.Duration {
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t1 := time.Now()
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f(n)
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return time.Since(t1)
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}
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t0 := time.Now()
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n := tries
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fails := 0
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for {
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runtime.GC()
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t1 := timeF(n)
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runtime.GC()
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t2 := timeF(2 * n)
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// should be 2x (linear); allow up to 3x
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if t2 < 3*t1 {
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if false {
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fmt.Println(typ, "\t", time.Since(t0))
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}
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return
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}
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// If n ops run in under a second and the ratio
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// doesn't work out, make n bigger, trying to reduce
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// the effect that a constant amount of overhead has
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// on the computed ratio.
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if t1 < 1*time.Second {
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n *= 2
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continue
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}
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// Once the test runs long enough for n ops,
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// try to get the right ratio at least once.
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// If five in a row all fail, give up.
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if fails++; fails >= 5 {
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panic(fmt.Sprintf("%s: too slow: %d channels: %v; %d channels: %v\n",
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typ, n, t1, 2*n, t2))
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}
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}
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}
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func main() {
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checkLinear("chanSelect", 1000, func(n int) {
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const messages = 10
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c := make(chan bool) // global channel
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var a []chan bool // local channels for each goroutine
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for i := 0; i < n; i++ {
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d := make(chan bool)
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a = append(a, d)
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go func() {
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for j := 0; j < messages; j++ {
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// queue ourselves on the global channel
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select {
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case <-c:
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case <-d:
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}
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}
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}()
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}
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for i := 0; i < messages; i++ {
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// wake each goroutine up, forcing it to dequeue and then enqueue
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// on the global channel.
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for _, d := range a {
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d <- true
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}
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}
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})
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}
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