RFR: 8330027: Identity hashes of archived objects must be based on a reproducible random seed [v3]

[Ioi Lam]

On Wed, 24 Apr 2024 15:39:26 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> > I think it's better to just not compute the identity hash inside the VM thread. Here's what I tried
> > [iklam at ad95e2e](https://github.com/iklam/jdk/commit/ad95e2e8b00cb151617463af41648cdece2dfc7b)
> > We thought that forcing the identity hash computation would increase sharing across processes, as it would mean fewer updates of the object headers during run time. However, most of the heap objects in the CDS archive are not accessible by the application (they are part of the archived module graph, etc). Also the archive contains a large number of Strings, which are unlikely to need the identity hash (String has its own hashcode() method).
> > Since the reason is rather dubious, I think it's better to remove it and simplify the system.
> 
> I like that, that is simpler. Okay, then we will only call ihash from a single thread, so a global constant seed should be fine. I should be able to assert that, right?

AI think an assert can be added, since we don't allow any Java threads to be launched. So even test cases that run arbitrary Java code during -Xshare:dump (using Java agents of -XX:ArchiveHeapTestClass) will not be able to run any Java code outside of the main Java thread.

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PR Comment: https://git.openjdk.org/jdk/pull/18735#issuecomment-2075370432