Connecting Observable
dayaftereh opened this issue · comments
I'm not sure if the following behavior an issue or i'm on the wrong track. I want to have a producer observable from a single channel with the ability of rxgo.WithPublishStrategy() to broadcast the items to child observables. I'm creating the child observables by using Observable#Observe channel from the producer observable with rxgo.FromChannel, but when the child Observable is canceled via the context from context.WithCancel() the parent observable stops emitting items.
using: github.com/reactivex/rxgo/v2 v2.5.0
To Reproduce
The following test allows to reproduce the behavior:
import "github.com/reactivex/rxgo/v2"
func TestRxGo(t *testing.T) {
producerCtx, cancelProducer := context.WithCancel(context.Background())
// create a infinity producer with context for cancel
producer := rxgo.Create(
[]rxgo.Producer{func(ctx context.Context, next chan<- rxgo.Item) {
log.Print("create producer")
defer func() {
log.Print("producer done")
}()
i := 0
for {
timeout := time.After(time.Second * 1)
select {
case <-ctx.Done():
return
case <-timeout:
next <- rxgo.Of(i)
log.Printf("producer fire %d", i)
}
i = i + 1
}
}},
rxgo.WithPublishStrategy(),
rxgo.WithContext(producerCtx),
rxgo.WithBackPressureStrategy(rxgo.Drop),
)
// connect to the producer
producer.Connect(producerCtx)
// create a child observable to receive items from producer
append := func(index int, parent context.Context) rxgo.Observable {
observable := rxgo.FromChannel(
producer.Observe(),
rxgo.WithBackPressureStrategy(rxgo.Drop),
rxgo.WithContext(parent),
)
observable.DoOnNext(func(i interface{}) {
log.Printf("Observable %d: %v", index, i)
})
return observable
}
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
// create the first observable with own context for cancel
observable1Ctx, cancelObservable1 := context.WithCancel(context.Background())
append(1, observable1Ctx)
// create the second observable with own context for cancel
observable2Ctx, cancelObservable2 := context.WithCancel(context.Background())
append(2, observable2Ctx)
go func() {
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
log.Print("cancel 1 observable")
cancelObservable1()
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
log.Print("cancel 2 observable")
cancelObservable2()
}()
log.Print("wait for done")
<-observable2Ctx.Done()
log.Print("all observable canceled")
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
log.Printf("cancel the producer")
cancelProducer()
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
}The console output is:
=== RUN TestRxGo
2021/05/05 14:57:32 sleep 5
2021/05/05 14:57:32 create producer
2021/05/05 14:57:33 producer fire 0
2021/05/05 14:57:34 producer fire 1
2021/05/05 14:57:35 producer fire 2
2021/05/05 14:57:36 producer fire 3
2021/05/05 14:57:37 wait for done
2021/05/05 14:57:37 sleep 5
2021/05/05 14:57:37 producer fire 4
2021/05/05 14:57:37 Observable 1: 4
2021/05/05 14:57:37 Observable 2: 4
2021/05/05 14:57:38 producer fire 5
2021/05/05 14:57:38 Observable 2: 5
2021/05/05 14:57:38 Observable 1: 5
2021/05/05 14:57:39 producer fire 6
2021/05/05 14:57:39 Observable 2: 6
2021/05/05 14:57:39 Observable 1: 6
2021/05/05 14:57:40 producer fire 7
2021/05/05 14:57:40 Observable 2: 7
2021/05/05 14:57:40 Observable 1: 7
2021/05/05 14:57:41 producer fire 8
2021/05/05 14:57:41 Observable 2: 8
2021/05/05 14:57:41 Observable 1: 8
2021/05/05 14:57:42 cancel 1 observable
2021/05/05 14:57:42 sleep 5
2021/05/05 14:57:42 producer fire 9
##--> Missing Observable 2
##--> Missing producer fire
2021/05/05 14:57:47 cancel 2 observable
2021/05/05 14:57:47 all observable canceled
2021/05/05 14:57:47 sleep 5
##--> Missing producer fire
2021/05/05 14:57:52 cancel the producer
##--> Missing producer done
2021/05/05 14:57:52 sleep 5
--- PASS: TestRxGo (25.04s)
PASS
Expected behavior
Actually i what that the producer observable still emits items without blocking and creating child observables dynamically.
Using Observable.ForEach to forward the items from the producer i'm close to a working example, but with a ugly workaround using a boolflag, because Observable.ForEach is unable to stop emitting item from the producer.
Here is the test:
func TestRxGoWithForEach(t *testing.T) {
producerCtx, cancelProducer := context.WithCancel(context.Background())
// create a infinity producer with context for cancel
producer := rxgo.Create(
[]rxgo.Producer{func(ctx context.Context, next chan<- rxgo.Item) {
log.Print("create producer")
defer func() {
log.Print("producer done")
}()
i := 0
for {
timeout := time.After(time.Second * 1)
select {
case <-ctx.Done():
return
case <-timeout:
next <- rxgo.Of(i)
log.Printf("producer fire %d", i)
}
i = i + 1
}
}},
rxgo.WithPublishStrategy(),
rxgo.WithContext(producerCtx),
rxgo.WithBackPressureStrategy(rxgo.Drop),
)
// connect to the producer
producer.Connect(producerCtx)
// create a child observable to receive items from producer
append := func(index int, parent context.Context) rxgo.Observable {
observableCtx, cancel := context.WithCancel(context.Background())
observable := rxgo.Create(
[]rxgo.Producer{func(ctx context.Context, next chan<- rxgo.Item) {
log.Printf("create observable %d", index)
defer func() {
log.Printf("observable done %d", index)
}()
done := false
wait := producer.ForEach(
func(i interface{}) {
if !done {
next <- rxgo.Of(i)
} else {
log.Printf("ForEach observable %d", index)
}
},
func(err error) {
if !done {
next <- rxgo.Error(err)
}
},
func() {
cancel()
},
rxgo.WithContext(ctx),
)
select {
case <-observableCtx.Done():
case <-wait:
}
done = true
}},
rxgo.WithPublishStrategy(),
rxgo.WithContext(observableCtx),
rxgo.WithBackPressureStrategy(rxgo.Drop),
)
_, abort := observable.Connect(context.Background())
go func() {
<-parent.Done()
abort()
cancel()
}()
observable.DoOnNext(func(i interface{}) {
log.Printf("Observable %d: %v", index, i)
})
return observable
}
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
// create the first observable with own context for cancel
observable1Ctx, cancelObservable1 := context.WithCancel(context.Background())
append(1, observable1Ctx)
// create the second observable with own context for cancel
observable2Ctx, cancelObservable2 := context.WithCancel(context.Background())
append(2, observable2Ctx)
go func() {
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
log.Print("cancel 1 observable")
cancelObservable1()
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
log.Print("cancel 2 observable")
cancelObservable2()
}()
log.Print("wait for done")
<-observable2Ctx.Done()
log.Print("all observable canceled")
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
log.Printf("cancel the producer")
cancelProducer()
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
}and the console output:
=== RUN TestRxGoWithForEach
2021/05/06 08:45:40 sleep 5
2021/05/06 08:45:40 create producer
2021/05/06 08:45:41 producer fire 0
2021/05/06 08:45:42 producer fire 1
2021/05/06 08:45:43 producer fire 2
2021/05/06 08:45:44 producer fire 3
2021/05/06 08:45:45 create observable 1
2021/05/06 08:45:45 create observable 2
2021/05/06 08:45:45 wait for done
2021/05/06 08:45:45 sleep 5
2021/05/06 08:45:45 producer fire 4
2021/05/06 08:45:45 Observable 2: 4
2021/05/06 08:45:45 Observable 1: 4
2021/05/06 08:45:46 producer fire 5
2021/05/06 08:45:46 Observable 2: 5
2021/05/06 08:45:46 Observable 1: 5
2021/05/06 08:45:47 producer fire 6
2021/05/06 08:45:47 Observable 2: 6
2021/05/06 08:45:47 Observable 1: 6
2021/05/06 08:45:48 producer fire 7
2021/05/06 08:45:48 Observable 2: 7
2021/05/06 08:45:48 Observable 1: 7
2021/05/06 08:45:49 producer fire 8
2021/05/06 08:45:49 Observable 1: 8
2021/05/06 08:45:49 Observable 2: 8
2021/05/06 08:45:50 cancel 1 observable
2021/05/06 08:45:50 sleep 5
2021/05/06 08:45:50 observable done 1
2021/05/06 08:45:50 producer fire 9
2021/05/06 08:45:50 ForEach observable 1
2021/05/06 08:45:50 Observable 2: 9
2021/05/06 08:45:51 producer fire 10
2021/05/06 08:45:51 Observable 2: 10
2021/05/06 08:45:51 ForEach observable 1
2021/05/06 08:45:52 producer fire 11
2021/05/06 08:45:52 Observable 2: 11
2021/05/06 08:45:52 ForEach observable 1
2021/05/06 08:45:53 producer fire 12
2021/05/06 08:45:53 Observable 2: 12
2021/05/06 08:45:53 ForEach observable 1
2021/05/06 08:45:54 producer fire 13
2021/05/06 08:45:54 Observable 2: 13
2021/05/06 08:45:54 ForEach observable 1
2021/05/06 08:45:55 cancel 2 observable
2021/05/06 08:45:55 all observable canceled
2021/05/06 08:45:55 sleep 5
2021/05/06 08:45:55 observable done 2
2021/05/06 08:45:55 producer fire 14
2021/05/06 08:45:55 ForEach observable 2
2021/05/06 08:45:55 ForEach observable 1
2021/05/06 08:45:56 producer fire 15
2021/05/06 08:45:56 ForEach observable 2
2021/05/06 08:45:56 ForEach observable 1
2021/05/06 08:45:57 producer fire 16
2021/05/06 08:45:57 ForEach observable 2
2021/05/06 08:45:57 ForEach observable 1
2021/05/06 08:45:58 producer fire 17
2021/05/06 08:45:58 ForEach observable 2
2021/05/06 08:45:58 ForEach observable 1
2021/05/06 08:45:59 producer fire 18
2021/05/06 08:45:59 ForEach observable 2
2021/05/06 08:45:59 ForEach observable 1
2021/05/06 08:46:00 cancel the producer
2021/05/06 08:46:00 sleep 5
2021/05/06 08:46:00 producer done
--- PASS: TestRxGoWithForEach (25.05s)
PASS
I guess I know why that blocks
func (i *channelIterable) produce(ctx context.Context) {
defer func() {
i.mutex.RLock()
for _, subscriber := range i.subscribers {
close(subscriber)
}
i.mutex.RUnlock()
}()
for {
select {
case <-ctx.Done():
return
case item, ok := <-i.next:
if !ok {
return
}
i.mutex.RLock()
for _, subscriber := range i.subscribers {
subscriber <- item
}
i.mutex.RUnlock()
}
}
}The subscriber channel is not listened to when the subscription context goes away. In your example (Observable 1 and Observable 2). So...It gets stuck in this for loop. @dayaftereh - when both adding and removing subscribers are also taken into account, then subscription leakage happens because closing one subscription context leads to pipeline block :(
@dayaftereh - I made some changes in the PR linked to allow unsubscribe. For testing purposes, I changed the producer part in your example to a channel based producer. Here is the modified test
func TestRxGo(t *testing.T) {
producerCtx, cancelProducer := context.WithCancel(context.Background())
// create a infinity producer with context for cancel
itemCh := make(chan Item)
go func() {
defer func() {
log.Print("producer done")
close(itemCh)
}()
i := 0
for {
select {
case <-producerCtx.Done():
return
case <-time.After(1 * time.Second):
select {
case <-producerCtx.Done():
return
case itemCh <- Of(i):
log.Printf("producer fire %d", i)
}
i++
}
}
}()
producer := FromChannel(itemCh,
WithPublishStrategy(),
WithContext(producerCtx),
WithBackPressureStrategy(Drop))
// connect to the producer
producer.Connect(producerCtx)
// create a child observable to receive items from producer
append := func(index int, parent context.Context) {
producer.DoOnNext(func(i interface{}) {
log.Printf("Observable %d: %v", index, i)
}, WithContext(parent))
}
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
// create the first observable with own context for cancel
observable1Ctx, cancelObservable1 := context.WithCancel(context.Background())
append(1, observable1Ctx)
// create the second observable with own context for cancel
observable2Ctx, cancelObservable2 := context.WithCancel(context.Background())
append(2, observable2Ctx)
go func() {
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
log.Print("cancel 1 observable")
cancelObservable1()
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
log.Print("cancel 2 observable")
cancelObservable2()
}()
log.Print("wait for done")
<-observable2Ctx.Done()
log.Print("all observable canceled")
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
log.Printf("cancel the producer")
cancelProducer()
log.Printf("sleep 5")
time.Sleep(time.Second * 5)
}And..........Here is the output
=== RUN TestRxGo
2021/11/04 13:34:22 sleep 5
2021/11/04 13:34:23 producer fire 0
2021/11/04 13:34:24 producer fire 1
2021/11/04 13:34:25 producer fire 2
2021/11/04 13:34:26 producer fire 3
2021/11/04 13:34:27 wait for done
2021/11/04 13:34:27 sleep 5
2021/11/04 13:34:27 producer fire 4
2021/11/04 13:34:27 Observable 2: 4
2021/11/04 13:34:27 Observable 1: 4
2021/11/04 13:34:28 producer fire 5
2021/11/04 13:34:28 Observable 2: 5
2021/11/04 13:34:28 Observable 1: 5
2021/11/04 13:34:29 producer fire 6
2021/11/04 13:34:29 Observable 2: 6
2021/11/04 13:34:29 Observable 1: 6
2021/11/04 13:34:30 producer fire 7
2021/11/04 13:34:30 Observable 1: 7
2021/11/04 13:34:30 Observable 2: 7
2021/11/04 13:34:31 producer fire 8
2021/11/04 13:34:31 Observable 2: 8
2021/11/04 13:34:31 Observable 1: 8
2021/11/04 13:34:32 cancel 1 observable
2021/11/04 13:34:32 sleep 5
2021/11/04 13:34:32 producer fire 9
2021/11/04 13:34:32 Observable 2: 9
2021/11/04 13:34:33 producer fire 10
2021/11/04 13:34:33 Observable 2: 10
2021/11/04 13:34:34 producer fire 11
2021/11/04 13:34:34 Observable 2: 11
2021/11/04 13:34:35 producer fire 12
2021/11/04 13:34:35 Observable 2: 12
2021/11/04 13:34:36 producer fire 13
2021/11/04 13:34:36 Observable 2: 13
2021/11/04 13:34:37 cancel 2 observable
2021/11/04 13:34:37 all observable canceled
2021/11/04 13:34:37 sleep 5
2021/11/04 13:34:37 producer fire 14
2021/11/04 13:34:38 producer fire 15
2021/11/04 13:34:39 producer fire 16
2021/11/04 13:34:40 producer fire 17
2021/11/04 13:34:41 producer fire 18
2021/11/04 13:34:42 cancel the producer
2021/11/04 13:34:42 sleep 5
2021/11/04 13:34:42 producer done
--- PASS: TestRxGo (25.01s)
PASS
Perfect.