RFR: 8275338: Add JFR events for notable serialization situations [v4]

[Raffaello Giulietti]

On Tue, 19 Dec 2023 15:56:39 GMT, Raffaello Giulietti <rgiulietti at openjdk.org> wrote:

> > Is it per class for each classloader that loads it? Or is it per class per JVM? It's more out of curiosity than anything else because I don't think it makes a big difference (I don't expect too many classloaders that would lead to the case of extremely large streams of events).
> 
> The checks are done on the `Class<?>` instance, that is, per each defined (as per JVMS) and _used_ serializable class, on first usage in serialization. If enabled at all, they are invoked by the private `ObjectStreamClass` constructor.

Well, in fact `ObjectStreamClass` maintains a cache of `Class<?>` -> `ObjectStreamClass` to avoid creating a new instance of `ObjectStreamClass` each time a `Class<?>` is looked up. It memoizes the association the first time.

However, the cache can be emptied under high memory pressure, so the `ObjectStreamClass` instance might be recreated later, thus re-invoking the serialization checker once again.

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PR Comment: https://git.openjdk.org/jdk/pull/17129#issuecomment-1863090984