Difference between Call and Send

[4xlan]

Hi,
just tried to dive into this framework (never had experience with the Erlang/OTP) and faced a strange issue.

I tried to create a chain of synchronous calls based on the generated code (application-supervisor-3 actors, just calling one another: A->B->C with the returning of answer C->B->A).

But every call is rejected with "not allowed". As I understand, this is due to the process status. At the same time, the process should wake up if there is something in the mailbox.

I may be missing something, but how can something be added to the mailbox if the very operation of adding to the mailbox checks a status that returns false due to the sleeping process because there are no messages in the mailbox?

Send, meanwhile, uses IsAlive, which allows the Sleep status, and therefore it works stably (but it doesn’t return a response, so it’s not quite suitable for my task).

So, the questions here are next:

Would you kindly to tell me, please, is there any description of the difference between Send and Call?
And if it is expected behaviour of Call, then is there something that should be done to wake up the actor?

Thank you for attention to this matter.

[halturin]

Could you please share your code? Its difficult to say whitout seeing it.

Send method allows you to send a message asynchrounously.
Call - to make a synchronous request.

see documentation for the details https://docs.ergo.services/basics/process#process-states

[4xlan]

still not sure if i follow your idea :)

Oh... I wish I could follow it by myself
Let me make it more complex then, but I'm afraid that it will go offtopic.

---

Let's assume that we have the some k8s operator, which listens to events in k8s namespace. As it is done with the SDK, we have to operate with the Reconcile func, which is called for each event, which fits the conditions.

Inside of this Reconcile, it is supposed to perform some operation with the content of the k8s resource, including the storage in the DB. For this purpose, we have two additional packages - content and cache manager.

Communication chain looks like: k8s op. -> content manager -> cache (db) manager.

In some cases cache manager can return data to content manager (to prepare an update for k8s resource), and content manager can pass it to k8s op. to update the resource in the namespace.

I'm trying now to figure out - is it possible to include the ergo in this chain as a message system. Currently, I have a feeling, that probably I should try to init node/actors in main (without autogenerated structure) and somehow pass the pointers to the structs of exact actors to the structures of k8s op./cache/content mgr.

Probably is there any best practices for this framework, regarding similar cases? Or it is everything about the actor model and the main recommendation is go deeper to model description?

[halturin]

I'm not familiar with the k8s internals and its API, but...

I think you can use gen.Node.Send method inside of Reconcile function to send messages to any process (even to the remote ones). The thing is you can use gen.Node interface wherever you want in your code while gen.Process interface can be used inside of your Actor callbacks only.

PS: is Reconcile the callback that invoked by SDK internals?

[halturin]

you can get gen.Node interface on starting your node from ergo.StartNode(...) or using gen.Process.Node() in your Actor callback (HandleMessage, for instance)

[4xlan]

Understood, will try, thank you!

PS: is Reconcile the callback that invoked by SDK internals?

Not sure that it is a callback, but this function called for each change in k8s cluster, there is a description.

[4xlan]

To, probably, finish this topic with some logical ending.

Just tried abovementioned option here.
All these examples above can be shortened to two conditions:

1. Actor should be possible to reach the functions of the "another packet"
2. "Another packet" should be able to call something from the actor.

To reach this goal I had to do some strange message exchange from Svc1 to Act1 and back, to have necessary links on both structs. This exchange works well, I think, because of Send's usage.

Solution itself looks really lousy, and ProxyCall was the last chance to check whether this approach is working or not (it was really naive hope that if I will use Call from the actor directly, it will solve everything), but, at least, I've checked the theory.

Unfortunately, no luck and I still have this "not allowed" when trying to call the svc2. Mayhaps I'm still missing something, will get back to this investigation later.