RFR: 8306582: Remove MetaspaceShared::exit_after_static_dump()

[Ioi Lam]

On Mon, 17 Jul 2023 17:14:01 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/cds/heapShared.hpp line 288:
> 
>> 286:     36137, // prime number
>> 287:     AnyObj::C_HEAP,
>> 288:     mtClassShared> ResolvedReferenceScratchTable;
> 
> You are using `oop->identity_hash()` as the key for this table. However, it's possible for two `resolved_references` arrays to have the exact same identity. It's better to to use `ResourceHashtable<OopHandle, OopHandle, ...` for this table. Then, you need to define two custom functions for these two parameters for `ResourceHashtable`
> 
> 
>     unsigned (*HASH)  (K const&),
>     bool     (*EQUALS)(K const&, K const&)
> 
> where the `K` type is `OopHandle`.
> 
> The `HASH` function can return `OopHandle::resolve()->identity_hash()` and the `EQUALS` function can compare the values of `OopHandle::resolve()`.
> 
> For the coding style, you can search for tables that use `HeapShared::oop_hash` for examples.

Actually, using `Oophandle` is too complicated. You can just use the `ConstantPool*` as the key, since each original `resolved_references` array is associated with a unique  `ConstantPool*`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14879#discussion_r1265941938