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// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package syncs
import (
"math"
"runtime"
"sync"
"sync/atomic"
"testing"
"golang.org/x/sys/cpu"
)
func TestShardValue(t *testing.T) {
type intVal struct {
atomic.Int64
_ cpu.CacheLinePad
}
t.Run("One", func(t *testing.T) {
sv := NewShardValue[intVal]()
sv.One(func(v *intVal) {
v.Store(10)
})
var v int64
for i := range sv.shards {
v += sv.shards[i].Load()
}
if v != 10 {
t.Errorf("got %v, want 10", v)
}
})
t.Run("All", func(t *testing.T) {
sv := NewShardValue[intVal]()
for i := range sv.shards {
sv.shards[i].Store(int64(i))
}
var total int64
sv.All(func(v *intVal) bool {
total += v.Load()
return true
})
// triangle coefficient lower one order due to 0 index
want := int64(len(sv.shards) * (len(sv.shards) - 1) / 2)
if total != want {
t.Errorf("got %v, want %v", total, want)
}
})
t.Run("Len", func(t *testing.T) {
sv := NewShardValue[intVal]()
if got, want := sv.Len(), runtime.NumCPU(); got != want {
t.Errorf("got %v, want %v", got, want)
}
})
t.Run("distribution", func(t *testing.T) {
sv := NewShardValue[intVal]()
goroutines := 1000
iterations := 10000
var wg sync.WaitGroup
wg.Add(goroutines)
for i := 0; i < goroutines; i++ {
go func() {
defer wg.Done()
for i := 0; i < iterations; i++ {
sv.One(func(v *intVal) {
v.Add(1)
})
}
}()
}
wg.Wait()
var (
total int64
distribution []int64
)
t.Logf("distribution:")
sv.All(func(v *intVal) bool {
total += v.Load()
distribution = append(distribution, v.Load())
t.Logf("%d", v.Load())
return true
})
if got, want := total, int64(goroutines*iterations); got != want {
t.Errorf("got %v, want %v", got, want)
}
if got, want := len(distribution), runtime.NumCPU(); got != want {
t.Errorf("got %v, want %v", got, want)
}
mean := total / int64(len(distribution))
for _, v := range distribution {
if v < mean/10 || v > mean*10 {
t.Logf("distribution is very unbalanced: %v", distribution)
}
}
t.Logf("mean: %d", mean)
var standardDev int64
for _, v := range distribution {
standardDev += ((v - mean) * (v - mean))
}
standardDev = int64(math.Sqrt(float64(standardDev / int64(len(distribution)))))
t.Logf("stdev: %d", standardDev)
if standardDev > mean/3 {
t.Logf("standard deviation is too high: %v", standardDev)
}
})
}
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