Fix memory leak in PerThreadPersistentClients

[Boberkraft]

Hello. I noticed two memory leaks:

1. To set clients, we were using thread.thread_variable_set(@key), but we read them via thread[@key]. Since one is Thread-local and the other Fiber-local, we were never finding any clients to close
2. The thread variable symbol @key was leaking (https://redmine.ruby-lang.org/issues/19333)

To fix both, i used this pattern that you have used previously used socketry/async-http@fcf231a#diff-df1daaada169fc5385e7257d57137dc5e11165a5551dda1ccc17f7546f1c360bR8

Types of Changes

• Bug fix.

Contribution

• I added tests for my changes.
• I tested my changes locally.
• I agree to the Developer's Certificate of Origin 1.1.

[Boberkraft]

Actually i misunderstood what this code actually does, so my fix is wrong, as it will close all clients

[ioquatix]

Thanks, actually something doesn't look quite right in this code. Let me review it.

[Boberkraft]

I wanted also to fix the deleting of thread variable, since it's leaky:

    179: def close
    180: 	Thread.list.each do |thread|
 => 181: 		binding.pry
    182: 
    183: 		if clients = thread.thread_variable_get(@key)
    184: 			thread.thread_variable_set(@key, nil)
    185: 
    186: 			clients.close
    187: 		end
    188: 	end
    189: end

3.4.3 :001 > thread.thread_variable_get(@key)
=> #<Async::HTTP::Faraday::PersistentClients:0x000000012d614828
 ...>
3.4.3 :001 > thread.thread_variable_set(@key, nil)
=> nil
3.4.3 :001 > thread.thread_variables
=> [:sentry_hub, :"Async::HTTP::Faraday::PerThreadPersistentClients_15176"]

But i don't think it's possible without adding something like a hash as a thread variables that will hold the clients

[ioquatix]

This has been discussed: https://bugs.ruby-lang.org/issues/19333

IIRC, Matz accepted this change so maybe we could implement it. I was probably too conservative not to implement it... it might break stuff. But I think that this use case is valid so we should fix it.

Do you want to make a PR to CRuby?

[Boberkraft]

I might try on weekend. I have never touched CRuby. We will see :)