RFR (S): 8223177: Data race on JvmtiEnvBase::_tag_map in double-checked locking

[David Holmes]

Hi Man,

On 1/05/2019 11:51 am, Man Cao wrote:
> Hi all,
> 
> Can I have reviews for this small change that adds memory fences for 
> double-checked locking?
> We found this race while working on the Java ThreadSanitizer project.
> 
> Webrev: https://cr.openjdk.java.net/~manc/8223177/webrev.00/
> Bug: https://bugs.openjdk.java.net/browse/JDK-8223177

Looks fine. One query in jvmtiTagMap.cpp - Was there a particular reason 
you moved the set_tag_map out of the constructor? (It's a common pattern 
when objects are bi-directionally linked to do it in the constructor.)

Thanks,
David

> -Man