RFR: 8225690: Multiple AttachListener threads can be created

[Yasumasa Suenaga]

Hi all,

Please review this change:

   JBS: https://bugs.openjdk.java.net/browse/JDK-8225690
   webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8225690/webrev.00/

This issue has been discussed on [1] and [2].
This webrev passed tests on submit repo 
(mach5-one-ysuenaga-JDK-8225690-20190704-1214-3626907).

It includes the fix for JDK-8225193. They relate each other, so I fix 
them together.


Thanks,

Yasumasa


[1] 
https://mail.openjdk.java.net/pipermail/serviceability-dev/2019-July/028585.html
[2] 
https://mail.openjdk.java.net/pipermail/serviceability-dev/2019-June/028418.html