mirror of
https://github.com/golang/go.git
synced 2025-10-31 16:50:58 +00:00
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>
94 lines
2.1 KiB
Go
94 lines
2.1 KiB
Go
// +build darwin linux
|
|
// run
|
|
|
|
// Copyright 2014 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
// Test that dequeueing from a pending channel doesn't
|
|
// take linear time.
|
|
|
|
package main
|
|
|
|
import (
|
|
"fmt"
|
|
"runtime"
|
|
"time"
|
|
)
|
|
|
|
// checkLinear asserts that the running time of f(n) is in O(n).
|
|
// tries is the initial number of iterations.
|
|
func checkLinear(typ string, tries int, f func(n int)) {
|
|
// Depending on the machine and OS, this test might be too fast
|
|
// to measure with accurate enough granularity. On failure,
|
|
// make it run longer, hoping that the timing granularity
|
|
// is eventually sufficient.
|
|
|
|
timeF := func(n int) time.Duration {
|
|
t1 := time.Now()
|
|
f(n)
|
|
return time.Since(t1)
|
|
}
|
|
|
|
t0 := time.Now()
|
|
|
|
n := tries
|
|
fails := 0
|
|
for {
|
|
runtime.GC()
|
|
t1 := timeF(n)
|
|
runtime.GC()
|
|
t2 := timeF(2 * n)
|
|
|
|
// should be 2x (linear); allow up to 3x
|
|
if t2 < 3*t1 {
|
|
if false {
|
|
fmt.Println(typ, "\t", time.Since(t0))
|
|
}
|
|
return
|
|
}
|
|
// If n ops run in under a second and the ratio
|
|
// doesn't work out, make n bigger, trying to reduce
|
|
// the effect that a constant amount of overhead has
|
|
// on the computed ratio.
|
|
if t1 < 1*time.Second {
|
|
n *= 2
|
|
continue
|
|
}
|
|
// Once the test runs long enough for n ops,
|
|
// try to get the right ratio at least once.
|
|
// If five in a row all fail, give up.
|
|
if fails++; fails >= 5 {
|
|
panic(fmt.Sprintf("%s: too slow: %d channels: %v; %d channels: %v\n",
|
|
typ, n, t1, 2*n, t2))
|
|
}
|
|
}
|
|
}
|
|
|
|
func main() {
|
|
checkLinear("chanSelect", 1000, func(n int) {
|
|
const messages = 10
|
|
c := make(chan bool) // global channel
|
|
var a []chan bool // local channels for each goroutine
|
|
for i := 0; i < n; i++ {
|
|
d := make(chan bool)
|
|
a = append(a, d)
|
|
go func() {
|
|
for j := 0; j < messages; j++ {
|
|
// queue ourselves on the global channel
|
|
select {
|
|
case <-c:
|
|
case <-d:
|
|
}
|
|
}
|
|
}()
|
|
}
|
|
for i := 0; i < messages; i++ {
|
|
// wake each goroutine up, forcing it to dequeue and then enqueue
|
|
// on the global channel.
|
|
for _, d := range a {
|
|
d <- true
|
|
}
|
|
}
|
|
})
|
|
}
|