Currently, many CDS operations are guarded by various global variables, such as DumpSharedSpaces and DynamicDumpSharedSpaces. There are also ad-hoc capabilities function like HeapShared::can_write(). So we have code like this where it's not clean what the intended condition us.

  if (DumpSharedSpaces && HeapShared::can_write()) {
    _narrow_oop_mode = CompressedOops::mode();
    _narrow_oop_base = CompressedOops::base();
    _narrow_oop_shift = CompressedOops::shift();
  }

We should have higher-level functions for checking/setting CDS configuration. E.g.,

  if (CDSConfig::is_dumping_heap()) {
    _narrow_oop_mode = CompressedOops::mode();
    _narrow_oop_base = CompressedOops::base();
    _narrow_oop_shift = CompressedOops::shift();
  }

In Leyden, we are implementing more capabilities in CDS that need to be conditionalized, so a more coherent set of configuration API is needed.

This RFE is to upstream the relevant part of the CDSConfig API from the Leyden repo to the mainline JDK repo:

https://github.com/openjdk/leyden/blob/7fe445527b18ae72da0848ea8a4792fc305181ad/src/hotspot/share/cds/cdsConfig.hpp

=============
Note: today we have a few high-level functions like Arguments::is_dumping_archive().

https://github.com/openjdk/jdk/blob/e25a49a993f270c33f7929e629fb3075a11fdec9/src/hotspot/share/runtime/arguments.hpp#L528-L532

For better modularity, these function should be moved to a new class.

To simplify review, this RFE is divided into multiple sub tasks.