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test: make tests deterministic with -scheduler=threads #4640

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Dec 6, 2024
+31 −12
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test: make tests deterministic with -scheduler=threads #4640

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27 changes: 22 additions & 5 deletions testdata/channel.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@ package main
import (
"runtime"
"sync"
"sync/atomic"
"time"
)

Expand Down Expand Up @@ -70,11 +71,13 @@ func main() {
// Test multi-receiver.
ch = make(chan int)
wg.Add(3)
go fastreceiver(ch)
go fastreceiver(ch)
go fastreceiver(ch)
var result atomic.Uint32
go fastreceiveradd(ch, &result)
go fastreceiveradd(ch, &result)
go fastreceiveradd(ch, &result)
slowsender(ch)
wg.Wait()
println("sum of sums:", result.Load())

// Test iterator style channel.
ch = make(chan int)
Expand All @@ -88,7 +91,10 @@ func main() {
println("sum(100):", sum)

// Test simple selects.
go selectDeadlock() // cannot use waitGroup here - never terminates
wg.Add(1)
go selectDeadlock()
wg.Wait()
Comment on lines -91 to +96
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Interestingly this was easily fixable using a WaitGroup.


wg.Add(1)
go selectNoOp()
wg.Wait()
Expand Down Expand Up @@ -244,7 +250,7 @@ func receive(ch <-chan int) {
func sender(ch chan int) {
for i := 1; i <= 8; i++ {
if i == 4 {
time.Sleep(time.Microsecond)
time.Sleep(time.Millisecond)
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This seems to be long enough to make the test deterministic with the Go toolchain.
But of course it's still racy, if it becomes a problem we can try to find another way using a WaitGroup or something.

println("slept")
}
ch <- i
Expand Down Expand Up @@ -290,6 +296,16 @@ func fastreceiver(ch chan int) {
wg.Done()
}

func fastreceiveradd(ch chan int, result *atomic.Uint32) {
sum := 0
for i := 0; i < 2; i++ {
n := <-ch
sum += n
}
result.Add(uint32(sum))
wg.Done()
}

func iterator(ch chan int, top int) {
for i := 0; i < top; i++ {
ch <- i
Expand All @@ -300,6 +316,7 @@ func iterator(ch chan int, top int) {

func selectDeadlock() {
println("deadlocking")
wg.Done()
select {}
println("unreachable")
}
Expand Down
4 changes: 1 addition & 3 deletions testdata/channel.txt
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Expand Up @@ -12,9 +12,7 @@ received num: 8
recv from closed channel: 0 false
complex128: (+7.000000e+000+1.050000e+001i)
sum of n: 149
sum: 25
sum: 29
sum: 33
sum of sums: 87
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These numbers were spread out differently when using threading. Sometimes the right numbers came out, but other times the numbers were balanced differently. Of course that's all correct: the important part is that every number is received by exactly one receiver.

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The mathematician in me really wants this to switch from adding integers to multiplying unique primes so that we can be sure (due to https://en.wikipedia.org/wiki/Fundamental_theorem_of_arithmetic ) that everything was received exactly once.

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Actually that's not a bad idea!
Not sure I'll make that PR, but you're free to do so of course :)

sum(100): 4950
deadlocking
select no-op
Expand Down
2 changes: 1 addition & 1 deletion testdata/goroutines.go
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Expand Up @@ -96,8 +96,8 @@ func acquire(m *sync.Mutex) {
m.Lock()
println("acquired mutex from goroutine")
time.Sleep(2 * time.Millisecond)
println("releasing mutex from goroutine")
m.Unlock()
println("released mutex from goroutine")
}

func sub() {
Expand Down
2 changes: 1 addition & 1 deletion testdata/goroutines.txt
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Expand Up @@ -19,7 +19,7 @@ closure go call result: 1
pre-acquired mutex
releasing mutex
acquired mutex from goroutine
released mutex from goroutine
releasing mutex from goroutine
re-acquired mutex
done
called: Foo.Nowait
Expand Down
8 changes: 6 additions & 2 deletions testdata/recover.go
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Expand Up @@ -2,9 +2,11 @@ package main

import (
"runtime"
"time"
"sync"
)

var wg sync.WaitGroup

func main() {
println("# simple recover")
recoverSimple()
Expand Down Expand Up @@ -113,14 +115,16 @@ func deferPanic() {
}

func runtimeGoexit() {
wg.Add(1)
go func() {
defer func() {
println("Goexit deferred function, recover is nil:", recover() == nil)
wg.Done()
}()

runtime.Goexit()
}()
time.Sleep(time.Millisecond)
wg.Wait()
}

func printitf(msg string, itf interface{}) {
Expand Down