RFR: 8266744: Make AbstractGangTask stack-allocatable only

[Kim Barrett]

On Fri, 7 May 2021 14:44:58 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Remove the inheritance relation in `class AbstractGangTask : public CHeapObj<mtInternal>`, and export necessary classes.

I don't think this change should be made. HotSpot has many classes that are optionally c-heap allocated; there's nothing special about that concept. Forcing the explosure of RestorePreservedMarksTask just to avoid that doesn't seem like an improvement to me.  Also, I really dislike the "Proxy" suffix renaming for the G1AbstractSubTask.  (That's another consequence of exposing the RestorePreservedMarksTask class, though there are other, not necessarily better solutions, such as global namespace qualifiying references where needed.)

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PR: https://git.openjdk.java.net/jdk/pull/3918