[crac] RFR: Allow users to pass new properties on restore

[Anton Kozlov]

On Thu, 14 Apr 2022 15:07:22 GMT, Ashutosh Mehra <duke at openjdk.java.net> wrote:

> VM changes: To identify properties that can be modified on restore,
> added a new bool field SystemProperty::_modifiable_on_restore.
> All the jdk related properties are marked unmodifiable. Rest of the
> properties are considered modifiable.
> When the JVM is launched with -XX:CRaCRestoreFrom option, then the
> properties prefixed with "-D" are maintained in a separate list in
> Arguments::_system_properties_for_restore. This list is passed to the JVM
> being restored by writing to a shared memory object.
> When the JVM is restored, it reads the new properties from shared memory
> object and updates its existing list of properties maintained in
> Arguments::_system_properties.
> 
> JDK changes: System::props needs to be updated on restore to account for
> new system properties. For this purpose j.l.System registers a new
> JDKResource which queries new properties from the VM in afterRestore()
> notification and updates System::props. The JDKResource registered by
> j.l.System is given highest priority so it is the first resource to get
> afterRestore() notification.
> 
> Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>

Thanks for the patch! The change is big, so I'd need some time to read and understand this.

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PR: https://git.openjdk.java.net/crac/pull/21