[11u] RFR/RFA (S): 8253134: JMM_VERSION should remain at 0x20020000 (JDK 10) in JDK 11

[Hohensee, Paul]

Please review this patch and CSR for 11.0.9. If approved, I propose tagging the issue with jdk11u-critical-request.

Bug: https://bugs.openjdk.java.net/browse/JDK-8253134
CSR: https://bugs.openjdk.java.net/browse/JDK-8253136
Webrev: http://cr.openjdk.java.net/~phh/8253134/webrev.11u.00/

JDK-8231209<https://bugs.openjdk.java.net/browse/JDK-8231209>, which was originally pushed to JDK 14, has been backported to 11.0.9 and 11,0.10-oracle. Those backports changed JMM_VERSION from 0x20020000 (JDK 10) to 0x20030000 (JDK 14), which introduced an incompatibility that was overlooked in the backport CSRs JDK-8247807<https://bugs.openjdk.java.net/browse/JDK-8247807> (11.0.9) and JDK-8248871<https://bugs.openjdk.java.net/browse/JDK-8248871> (11.0.10-oracle). JDK 11 users checking for JMM_VERSION == 0x20020000 will find 0x2003000 instead and possibly abort. The issue was first noticed as part of reviewing a backport of JDK-8185003<https://bugs.openjdk.java.net/browse/JDK-8185003> to JDK 8: see the Description in the corresponding CSR JDK-8251498<https://bugs.openjdk.java.net/browse/JDK-8251498>.

For the reasons detailed there, JMM_VERSION in JDK 11 should be reverted to 0x20020000 (JDK 10), and the @since javadoc tag for com.sun.management.ThreadMXBean.getCurrentThreadAllocatedBytes should be changed from 14 to 11.0.9. If/when the JDK-8231209<https://bugs.openjdk.java.net/browse/JDK-8231209> backport to JDK 8 is approved for openjdk8u282, the @since tag should be changed to 8u282.

Thanks,
Paul