Integrated: 8212107: VMThread issues and cleanup

[Robbin Ehn]

On Thu, 17 Sep 2020 19:58:02 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

> We simplify the vmThread by removing the queue and refactor the the main loop.
> This solves the issues listed:
> - It can create an extra safepoint directly after a safepoint.
> - It's not safe for a non-JavaThread to add safepoint to queue while GC do oops do.
> - The exposure of the vm operation is dangerous if it's a handshake.
> - The code is a hornets nest with the repetition of checks and branches
> 
> Passes t1-8, and a benchmark run.
> 
> If you want a smaller diff the commits contains the incremental progress and each commit passed t1.

This pull request has now been integrated.

Changeset: 431338bc
Author:    Robbin Ehn <rehn at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/431338bc
Stats:     480 lines in 8 files changed: 146 ins; 259 del; 75 mod

8212107: VMThread issues and cleanup

Reviewed-by: shade, dcubed, coleenp, dholmes, redestad

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PR: https://git.openjdk.java.net/jdk/pull/228