On Mon, 17 Jul 2023 17:14:01 GMT, Ioi Lam <ik...@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*`.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/14879#discussion_r1265941938
