From: "Eregon (Benoit Daloze) via ruby-core" <ruby-core@...>
Date: 2023-01-18T15:58:08+00:00
Subject: [ruby-core:111885] [Ruby master Feature#19333] Setting (Fiber Local|Thread Local|Fiber Storage) to nil should delete value in order to avoid memory leaks.

Issue #19333 has been updated by Eregon (Benoit Daloze).


There is also `Thread#key?` for Fiber locals, so not just `thread_variable?`.

Above I am talking more about the performance issue than the semantic incompatibility.
Doing delete+insert is more expensive than set+set, and even much more so if Fiber/Thread locals are implemented with Shape (which is already the case of TruffleRuby, so not theoretical).

----------------------------------------
Feature #19333: Setting (Fiber Local|Thread Local|Fiber Storage) to nil should delete value in order to avoid memory leaks.
https://bugs.ruby-lang.org/issues/19333#change-101302

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
----------------------------------------
As it stands, Fiber Locals, Thread Locals and Fiber Storage have no way of deleting key-value associations.

```ruby
100.times do |i|
  name = :"variable-#{i}"
  Thread.current[name] = 10
end
```

Because of this, dynamically generated associations can leak over time. This is worse for things like Threads that might be pooled (or maybe an argument against user-space pooling).

In any case, having a way to delete those associations would allow application code to at least delete the associations when they no longer make sense.

I propose that assigning `nil` to "locals" or "storage" should effectively delete them.

e.g.

```ruby
100.times do |i|
  name = :"variable-#{i}"
  Thread.current[name] = 10
  Thread.current[name] = nil # delete association
end
```

A more invasive alternative would be to define new interfaces like `Thread::Local`, `Fiber::Local` and `Fiber::Storage::Local` (or something) which correctly clean up on GC.



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