RFR: 8306582: Remove MetaspaceShared::exit_after_static_dump()

[Matias Saavedra Silva]

On Mon, 17 Jul 2023 16:55:03 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> Currently we exit the VM after static dumping with `MetaspaceShared::exit_after_static_dump()`. 
>> 
>> 
>>  // We have finished dumping the static archive. At this point, there may be pending VM
>>  // operations. We have changed some global states (such as vmClasses::_klasses) that
>>  // may cause these VM operations to fail. For safety, forget these operations and
>>  // exit the VM directly.
>>  void MetaspaceShared::exit_after_static_dump() {
>>    os::_exit(0);
>>  } 
>> 
>> 
>> As the comment suggests, the VM state is altered when preparing and performing the static dump, so this change aims to prevent these state changes so the VM can exit normally after the static dump completes. There are three major aspects to this change:
>> 1. Since the resolved references array in the Constant Pool is altered when preparing for a static dump, a "scratch copy" is created and archived instead 
>> 2. Symbols are sorted by address and have their hash recalculated. Similarly to point 1, the copies of the symbols that are to be archived have their hashes updated as opposed to the originals.
>> 3. The handling of -Xshare:dump during argument parsing such that the VM can continue and exit normally with an exit code of 0.
>
> src/hotspot/share/classfile/classLoaderData.cpp line 1085:
> 
>> 1083:     guarantee(this == class_loader_data(cl) || has_class_mirror_holder(), "Must be the same");
>> 1084:     guarantee(cl != nullptr || this == ClassLoaderData::the_null_class_loader_data() || has_class_mirror_holder(), "must be");
>> 1085:   }
> 
> Why is this necessary?

This seems to be a band-aid solution to a deeper problem: the java platform and system loaders are reset. I believe the correct solution is to restore these values after dumping completes

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PR Review Comment: https://git.openjdk.org/jdk/pull/14879#discussion_r1272766119