WeakRef requires rescuing RefError to avoid race condition

There's an race condition in the implied usage of WeakRef.

The API only has weakref_alive?, and then delegated access to the referenced object. But the delegated access to the object cannot be protected by weakref_alive? since GC may occur between the check and the usage.

This means we basically always have to check for RefError, which basically makes weakref_alive? useless if we want to actually potentially use the object.

WeakMap usage is discouraged, leaving us with needing to add this functionality to WeakRef, which may break if WeakRef implementation changes (i.e., there is no good solution for this).

This is discussed at length here:

https://stackoverflow.com/questions/69185508/ruby-weakref-has-implicit-race-condition

I would recommend an addition to the API that will safely return a (non-weak) object if it's alive, or else nil, and obviously it's up to the user to realize that this will stop GC from happening on that object while they hold it.

WeakRef API から始め、特に weakref_alive?、委譲アクセス、RefError の処理、推奨されない代替手段である WeakMap を確認してください。Race condition の文脈については、リンクされた Stack Overflow の議論を読んでください。完了とは、生存している場合は強い参照を持つオブジェクトを安全に返し、それ以外の場合は nil を返す API に合意し、実装することです。