RFR: 8306582: Remove MetaspaceShared::exit_after_static_dump()

[David Holmes]

On Thu, 13 Jul 2023 21:25:17 GMT, Matias Saavedra Silva <matsaave 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.

Hi Matias,

I'm not keen on having to teach the launcher about `-Xshare:dump` and that it is a terminal operation. But after looking into it I have to admit it is a cleaner and more consistent termination strategy. That said you need to be aware that this will now do a clean shutdown of the VM after the dump, so shutdown hooks will now run.

Lets see what core-libs folk think too.

Thanks.

src/hotspot/share/runtime/threads.cpp line 812:

> 810:   if (DumpSharedSpaces) {
> 811:     MetaspaceShared::preload_and_dump();
> 812:     *canTryAgain = false; // don't let caller call JNI_CreateJavaVM again

This is only set when create_vm fails. A successful creation of the VM prevents subsequent re-creation attempts.

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PR Review: https://git.openjdk.org/jdk/pull/14879#pullrequestreview-1531828953
PR Review Comment: https://git.openjdk.org/jdk/pull/14879#discussion_r1264773183