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// run
// Copyright 2017 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 locks don't go quadratic due to runtime hash table collisions.
package main
import (
"bytes"
"fmt"
"log"
"os"
"runtime"
"runtime/pprof"
"sync"
"time"
)
const debug = false
// checkLinear asserts that the running time of f(n) is at least linear but sub-quadratic.
// 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)
}
n := tries
fails := 0
var buf bytes.Buffer
inversions := 0
for {
t1 := timeF(n)
t2 := timeF(2 * n)
if debug {
println(n, t1.String(), 2*n, t2.String())
}
fmt.Fprintf(&buf, "%d %v %d %v (%.1fX)\n", n, t1, 2*n, t2, float64(t2)/float64(t1))
// should be 2x (linear); allow up to 3x
if t1*3/2 < t2 && t2 < t1*3 {
return
}
if t2 < t1 {
if inversions++; inversions >= 5 {
// The system must be overloaded (some builders). Give up.
return
}
continue // try again; don't increment fails
}
// Once the test runs long enough for n ops,
// try to get the right ratio at least once.
// If many in a row all fail, give up.
if fails++; fails >= 5 {
// If 2n 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 t2 < time.Second*4/10 {
fails = 0
n *= 2
continue
}
panic(fmt.Sprintf("%s: too slow: %d ops: %v; %d ops: %v\n\n%s",
typ, n, t1, 2*n, t2, buf.String()))
}
}
}
const offset = 251 // known size of runtime hash table
const profile = false
func main() {
if profile {
f, err := os.Create("lock.prof")
if err != nil {
log.Fatal(err)
}
pprof.StartCPUProfile(f)
defer pprof.StopCPUProfile()
}
checkLinear("lockone", 1000, func(n int) {
ch := make(chan int)
locks := make([]sync.RWMutex, offset+1)
for i := 0; i < n; i++ {
go func() {
locks[0].Lock()
ch <- 1
}()
}
time.Sleep(1 * time.Millisecond)
go func() {
for j := 0; j < n; j++ {
locks[1].Lock()
locks[offset].Lock()
locks[1].Unlock()
runtime.Gosched()
locks[offset].Unlock()
}
}()
for j := 0; j < n; j++ {
locks[1].Lock()
locks[offset].Lock()
locks[1].Unlock()
runtime.Gosched()
locks[offset].Unlock()
}
for i := 0; i < n; i++ {
<-ch
locks[0].Unlock()
}
})
if runtime.GOARCH == "arm" && os.Getenv("GOARM") == "5" {
// lockmany reliably fails on the linux-arm-arm5spacemonkey
// builder. See https://golang.org/issue/24221.
return
}
checkLinear("lockmany", 1000, func(n int) {
locks := make([]sync.RWMutex, n*offset+1)
var wg sync.WaitGroup
for i := 0; i < n; i++ {
wg.Add(1)
go func(i int) {
locks[(i+1)*offset].Lock()
wg.Done()
locks[(i+1)*offset].Lock()
locks[(i+1)*offset].Unlock()
}(i)
}
wg.Wait()
go func() {
for j := 0; j < n; j++ {
locks[1].Lock()
locks[0].Lock()
locks[1].Unlock()
runtime.Gosched()
locks[0].Unlock()
}
}()
for j := 0; j < n; j++ {
locks[1].Lock()
locks[0].Lock()
locks[1].Unlock()
runtime.Gosched()
locks[0].Unlock()
}
for i := 0; i < n; i++ {
locks[(i+1)*offset].Unlock()
}
})
}
|
