New Early Access builds

[Alan Bateman]

The builds at the Project Loom Early Access page [1] have been 
refreshed. The latest builds are based on jdk-16+25 (JDK 16 build 25).

There are important stability fixes in this build. We think this build 
should resolve most of the crashes that people have reported over the 
last few months when running with concurrent GCs. We are mostly testing 
with G1 and ZGC.  There may be a small performance impact in some cases 
with the changes but for now, it will be great if you have been seeing 
issues to re-test to see if there are any other issues.

One area that is currently not stable is the debugger support. We are 
mid way through a big re-implementation. The "new approach" upgrades JVM 
TI to fully support virtual threads so that the suspend/resume policies 
needed when debugging can be supported. It also avoids the thread 
identity issues that plagued the original approach. We hope to be at the 
point soon where we can engage with the IDE/debugger maintainers about 
adding support for virtual threads. We expect debuggers will need modest 
changes, esp. in areas where a debugger wants to track all threads or 
enumerate all threads or thread groups.

-Alan

[1] http://jdk.java.net/loom/