RFR: 8283237: CallSite should be a sealed class [v2]

[altrisi]

On Thu, 17 Mar 2022 08:07:23 GMT, liach <duke at openjdk.java.net> wrote:

>> Change `CallSite` to a sealed class, as `CallSite` is an abstract class which does not allow direct subclassing by users per its documentation. Since I don't have a JBS account, I posted the content for the CSR in a GitHub Gist at https://gist.github.com/150d5aa7f8b13a4deddf95969ad39d73 and wish someone can submit a CSR for me.
>
> liach has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Swap mutable and volatile in the permits list

Note that there's a class in tests (or something similar) that extends CallSite directly: https://github.com/openjdk/jdk/blob/d8893fad23d1ee6841336b96c34599643edb81ce/test/hotspot/jtreg/vmTestbase/vm/mlvm/patches/java.base/java/lang/invoke/NewInvokeSpecialCallSite.java

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PR: https://git.openjdk.java.net/jdk/pull/7840