Summary

Before JDK 5.0 (1.5.0) a platform with register windows did not flush the register windows when calling JNI. Therefore the VM thread could not read the java stack of a JavaThread in native. NeedsDeoptSuspend was set to true on such platforms, making the JavaThread flush the register windows and deoptimize on return from JNI instead. After JDK 1.5 both code paths work on all platforms, but with one of them much more complicated.

Problem

NeedsDeoptSuspend code path adds complexity without any notable difference for a user. The flag was never meant to be used by a user, the only noticeable effect the flag has had is it could crash the VM when changing it from it's default value.

Solution

Obsolete the flag (JDK 13) and remove the flag (JDK 14).

Specification

Mark the flag as obsolete in the flag table:

+   { "NeedsDeoptSuspend",             JDK_Version::undefined(), JDK_Version::jdk(13), JDK_Version::jdk(14) },

http://cr.openjdk.java.net/~rehn/8222637/webrev/