RFR(XS): 8241464: [11u] Backport: make rehashing be a needed guaranteed safepoint cleanup action

[Doerr, Martin]

Hi,

I'd like to backport a part of JDK-8221967. I'm using a new bug because it's only a part of the original one.
Original change has the summary "Move redundant table lookup and make rehashing be a needed guaranteed safepoint cleanup action."
The first part of it doesn't apply to 11u, because the SymbolTable and StringTable parts are different in 11u and I don't see the need to change them.

The second part of it does apply and makes perfect sense. Especially if BiasedLocking is disabled (11u BiasedLocking implementation requests more safepoints making this fix less important).

Original bug:
https://bugs.openjdk.java.net/browse/JDK-8221967

Original issue:
http://hg.openjdk.java.net/jdk/jdk/rev/2523496f5107

New webrev:
http://cr.openjdk.java.net/~mdoerr/8221967_string_table_partial_backport_11u/webrev.00/

Please review.

Best regards,
Martin