Mutiny support on Apollo Android (Java/kotlin) GraphQL client

[aoudiamoncef]

Hi @cescoffier @jponge,

I'm new to Mutiny, I tried to translate ReactorApollo to MutinyApollo.

I was a bit confused about Emitter and Cancelable. What is the equivalent of Disposable in Mutiny ?

Thanks

Moncef

[cescoffier]

Cancellable is equivalent to Disposable, I guess.

[aoudiamoncef]

In MonoSink has a Disposable to control it's lifecycle, but in Emitter there isn't
Cancelable which maked me confused. Ex

monoSink.onCancel(clone::cancel)

To achieve the same behavior in Mutiny, I used
uni.onCancellation().invoke(clone::cancel).

Is it correct ?

Thanks

[cescoffier]

There is an onTermination method that let you do the cleanup:

emitter.onTermination(() -> clone.cancel());

Otherwise, yes, you would need to use the onCancellation() group from the resulting Uni.

[aoudiamoncef]

Great, I'll use onTermination.

When I'm using Uni Emitter, I order to complete without any value, I should use emitter.complete(null) ?

What's the equivalent of CompositeDisposable in Mutiny ?

[cescoffier]

On Sun 27 Jun 2021 at 21:30, Moncef AOUDIA ***@***.***> wrote: Great, I'll use onTermination. When I'm using Uni Emitter, I order to complete without any value, I should use emitter.complete(null) ?

Yes, as Uni supports null value.

What's the equivalent of CompositeDisposable in Mutiny ?

I’ve no idea what that is. Is it just an aggregate of Disposable? —

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[aoudiamoncef]

Yes, it's just an aggregation of Disposables, I searched an equivalent in Mutiny JavaDocs but without success. One of the use cases is in Android applications to cancel a group of Disposables based on application states.

If the concept is coming to Mutiny I'll be happy to contribute.

Thanks for all answer's, I appreciate

[cescoffier]

I will let @jponge decide.
I don't see a lot of usages, but I may be wrong.

If we decide to add one, we need to have an immutable list as inputs (or concurrency can strike), iterable from last to first probably, and protect against exception. What happens when such an exception happens? do we stop, or ignore and continue?
It seems to be usecase sensitive.

[jponge]

First impression is that we don't want this feature.

If you want to manage multiple Uni then you should combine them (and I plan to rework this area soon).

[aoudiamoncef]

This feature is available in:

RxJava: please see JavaDoc, implementation, use case.

Reactor: please see JavaDoc, implementation, use case.

@jponge,
According to above implementations, it could be a utility class which manage a Collection of Cancellable in Mutiny.

[aoudiamoncef]

I would cancel/dispose Uni/multi from my callback, but I don't found any setter with Cancellable type.

Is there a way to achieve this in Mutiny ?

[cescoffier]

You don't cancel a uni/multi, you cancel a subscription.

I need to better understand what you mean by "any setting with Cancellable type".

[aoudiamoncef]

I'm sorry for ambiguous explications. I'll try to give a concrete example.

In RxJava there is FlowableEmitter which holds an instance of Disposable, we could use a custom implementation:

  private static Disposable getRx3Disposable(com.apollographql.apollo.internal.util.Cancelable cancelable) {
    return new Disposable() {
      @Override public void dispose() {
        cancelable.cancel();
      }

      @Override public boolean isDisposed() {
        return cancelable.isCanceled();
      }
    };
  }

then

  private static <T> void cancelOnFlowableDisposed(FlowableEmitter<T> emitter, com.apollographql.apollo.internal.util.Cancelable cancelable) {
    emitter.setDisposable(getRx3Disposable(cancelable));
  }

The complete example.

[cescoffier]

I looked at what these methods were intended to do. Let's be clear, it's confusing: setCancellable and setDisposable have the same javadoc! In addition, they are unrelated to the emitter or to the "subscription", they more or less "runnable" that gets attached when the emitter terminated (upon cancellation from the downstream, or item/failure emission from the emitter itself). So, their name is slightly confusing.

So, let's go back to your question:

Cancellable cancellable = ...;
Uni<T> uni = Uni.createFrom().emitter(emitter -> {
    emitter.onTermination(() -> cancellable.cancel());
});

Yes, that's it! Mutiny accepts a Runnable which is executed when the emitter terminates. You can do whatever you need to do in it, including "cancelling" or "closing" resources.