RFR: 8284161: Implementation of Virtual Threads (Preview) [v8]

[Paul Sandoz]

On Wed, 27 Apr 2022 14:24:20 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> This is the implementation of JEP 425: Virtual Threads (Preview); TBD which JDK version to target.
>> 
>> We will refresh this PR periodically to pick up changes and fixes from the loom repo.
>> 
>> Most of the new mechanisms in the HotSpot VM are disabled by default and require running with `--enable-preview` to enable.
>> 
>> The patch has support for x64 and aarch64 on the usual operating systems (Linux, macOS, and Windows). There are stubs (calling Unimplemented) for zero and some of the other ports. Additional ports can be contributed via PRs against the fibers branch in the loom repo.
>> 
>> There are changes in many areas. To reduce notifications/mails, the labels have been trimmed down for now to hotspot, serviceability and core-libs. We'll add the complete set of labels when the PR is further along.
>> 
>> The changes include a refresh of java.util.concurrent and ForkJoinPool from Doug Lea's CVS. These changes will probably be proposed and integrated in advance of this PR.
>> 
>> The changes include some non-exposed and low-level infrastructure to support the (in draft) JEPs for Structured Concurrency and Scope Locals. This is to make life a bit easier and avoid having to separate VM changes and juggle branches at this time.
>
> Alan Bateman has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Refresh 7965cc6b168e567ac2596f2fbc3b00a7d99b7e1e

It's great to see end game in play for this multi-year effort, impressive work by all involved.

I looked through code in the base module. Generally looks well structured and documented.

The fork join code is naturally hard to review. I did try! (it takes the prize for the highest Java code density in the JDK). I mostly looked for regular and repeated structure rather than trying to fully understand/review the intricate concurrency details.

IMO there is some post integration work to do around the architecture of thread containers, i presume the structured concurrency implementation (use of thread flock) will help with that.

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Marked as reviewed by psandoz (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/8166