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.

Beginnen Sie mit der WeakRef API, insbesondere mit weakref_alive?, dem delegierten Zugriff, der Behandlung von RefError und der nicht empfohlenen WeakMap-Alternative. Lesen Sie die verlinkte Stack Overflow-Diskussion zum Kontext der Race Condition; abgeschlossen ist die Aufgabe, wenn Sie sich auf eine API geeinigt und diese implementiert haben, die sicher ein stark referenziertes Objekt zurückgibt, wenn es noch lebt, oder andernfalls nil.