Context cascading Test - go

Question

How to improve this context cascading test:
func TestParentTimedoutContext(t *testing.T) {
ctx1, cancel := context.WithTimeout(context.Background(), 1*time.Millisecond)
defer cancel()
ctx2, cancel2 := context.WithTimeout(ctx1, 1000*time.Millisecond)
defer cancel2()
time.Sleep(15 * time.Millisecond) // make ctx1 timeout
if ctx2.Err() == nil {
t.Error("failed")
}
}
Command:
go test -timeout 30s -count=1 -run ^TestParentTimedoutContext$ my/internal/services
Output:
ok
Sometimes:
failed
go version go1.16.6

Answer 1

Wait for ctx2.Done() and measure time duration which should be less than ctx2 deadline.
Try this:
func TestParentTimedoutContext(t *testing.T) {
t0 := time.Now()
ctx1, cancel := context.WithTimeout(context.Background(), 1*time.Millisecond)
defer cancel()
ctx2, cancel2 := context.WithTimeout(ctx1, 1000*time.Millisecond)
defer cancel2()
<-ctx2.Done()
d := time.Since(t0)
if d > 777*time.Millisecond {
t.Error("failed:" + d.String())
}
}
Benchmark:
func BenchmarkParentTimedoutContext(b *testing.B) {
for i := 0; i < runtime.NumCPU(); i++ {
go func() {
ctx3, cancel3 := context.WithTimeout(context.Background(), 10_000*time.Millisecond)
defer cancel3()
for {
select {
case <-ctx3.Done():
return
default:
// runtime.Gosched()
}
}
}()
}
for i := 0; i < b.N; i++ {
ctx1, cancel1 := context.WithTimeout(context.Background(), 1*time.Millisecond)
ctx2, cancel2 := context.WithTimeout(ctx1, 1000*time.Millisecond)
<-ctx2.Done()
cancel1()
cancel2()
}
}
Benchmark result (Linux):
# BenchmarkParentTimedoutContext-8 589 17_178_588 ns/op // 17ms
Histogram code:
package main
import (
"context"
"fmt"
"runtime"
"time"
)
func main() {
const n = 1_000
for i := 0; i < runtime.NumCPU(); i++ {
go func() {
ctx3, cancel3 := context.WithTimeout(context.Background(), n*time.Millisecond)
defer cancel3()
for {
select {
case <-ctx3.Done():
return
default:
// runtime.Gosched()
}
}
}()
}
all := make([]time.Duration, n)
for i := 0; i < n; i++ {
t0 := time.Now()
ctx1, cancel1 := context.WithTimeout(context.Background(), 1*time.Millisecond)
ctx2, cancel2 := context.WithTimeout(ctx1, 1000*time.Millisecond)
<-ctx2.Done()
d := time.Since(t0)
cancel1()
cancel2()
all[i] = d
}
ave, x, y := histogram(all, 10)
fmt.Println("min =", y[0])
fmt.Println("max =", y[1])
fmt.Println("ave =", ave)
fmt.Println(x)
fmt.Println(y)
fmt.Println(runtime.GOOS, runtime.GOARCH, runtime.Version())
}
func histogram(d []time.Duration, n int) (ave time.Duration, x []int, y []time.Duration) {
x = make([]int, n)
y = make([]time.Duration, n+1)
min := d[0]
max := min
ave = min
for _, v := range d[1:] {
ave += v
if v < min {
min = v
} else if v > max {
max = v
}
}
ave /= time.Duration(len(d))
distance := (max - min) / time.Duration(n)
v := min
for i := range y {
y[i] = v
v += distance
}
y[len(y)-1] = max // compensate division error
for _, v := range d {
i := int((v - min) / distance)
if i >= n {
i--
}
x[i]++
}
return
}
Benchmark result (Linux):
go run .
min = 1.046524ms
max = 22.717866ms
ave = 2.090832ms
[950 0 0 0 0 0 1 0 47 2]
[1.046524ms 3.213658ms 5.380792ms 7.547926ms 9.71506ms 11.882194ms 14.049328ms 16.216462ms 18.383596ms 20.55073ms 22.717866ms]
linux amd64 go1.16.6