Porting Loom to additional architectures

[Alan Bateman]

Porters,

In Project Loom we expect to have one, maybe two, draft JEPs in the 
coming months to propose the Virtual Threads feature. We think the 
current implementation is far enough along, and stable enough, to start 
ports to other architectures.

As things stands, the repo has ports to x64 and aarch64 on the usual 
operating systems (Linux, macOS, and Windows). Oracle engineers are not 
planning to work on 32-bit x86 or other architectures. It's too early to 
talk about dates or releases but we think the underlying implementation 
is stable enough to make progress on additional ports. A port to 32-bit 
x86 is not required to go into the main line but it will lead to build 
breakage if it isn't contributed in advance.  I think with Project 
Panama that some ports (32-bit ARM?) were done after the initial 
integration, and that can work here too.

In terms of size, there are currently ~4200 lines of x64 specific code, 
and ~1800 lines of aarch64 specific code. There is more x64 code because 
it has an oopmap stub generator. The tests run in the existing tiers.

This is just a heads-up up for now, it's probably best to follow up on 
loom-dev with questions.

-Alan.