[ruby-core:117217] [Ruby master Feature#20276] Introduce Fiber interfaces for Blocking operations on Ractors

["forthoney (Seong-Heon Jung) via ruby-core" <ruby-core@ml.ruby-lang.org>]

Issue #20276 has been updated by forthoney (Seong-Heon Jung).


ioquatix (Samuel Williams) wrote in #note-7:
> If I had to take a guess, I'd say it's a bug with waiting on a Ractor while handling signals?

Under closer inspection, the `Thread#join` workaround should work in theory but actually deadlocks in practice, likely due to an implementation bug. [Here](https://bugs.ruby-lang.org/issues/20346)'s the relevant bug report. IRB is likely unresponsive because of this deadlock.

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Feature #20276: Introduce Fiber interfaces for Blocking operations on Ractors
https://bugs.ruby-lang.org/issues/20276#change-107303

* Author: forthoney (Seong-Heon Jung)
* Status: Feedback
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### Motivation
I am trying to build a web server with Ractors. The lifecycle for a request in the current implementation is 

1. main ractor sends request to worker ractor
2. worker ractor handles response
3. worker ractor sends response to main ractor
4. main ractor writes response
5. repeat

The main ractor utilizes the Async gem (specifically async-http) to handle connections concurrently, meaning each request is handled on a separate fiber.
The issue I am running into is after I send a request to a worker ractor, I need to do a blocking wait until I receive a response.
While I am waiting for the response, I cannot take any more connections.


### Solution
If the fiber scheduler had a hook for `Ractor.receive` or `Ractor#take` (both of which are blocking), the main ractor can send the message, handle other connections while the worker processes the request. When the worker produces a message, it will then take the reqeust and write it in the socket. Specifically, I think the `block` and `unblock` hooks should be implemented for Ractors, considering Threads and Mutexes already use them.




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