[crac] RFR: Clear JarFileFactory cache on checkpoint [v2]

[Alexey Bakhtin]

On Tue, 8 Feb 2022 13:57:14 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

> @alexeybakhtin pointed out that JarURLConnection.connect method was not synchronized with the JarFileFactory.beforeCheckpoint, which could lead to NPE due to entry cleaned from the cache while connect is executed. Now beforeCheckpoint detects JarFile entries that should be cleaned by moving them to a weak cache map for a short period of time.

Thank you.
LGTM

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PR: https://git.openjdk.java.net/crac/pull/14