RFR(XS) for PeriodicTask_lock cleanup (8072439)

[Daniel D. Daugherty]

Greetings,

My fix for the following bug:

     JDK-8047720 Xprof hangs on Solaris

that was pushed to JDK9 last June needs to be cleaned up.

Thanks to Alex Garthwaite (agarthwaite at twitter.com) and Carsten
Varming (varming at gmail.com) for reporting the mess that I made
in WatcherThread::stop() and for suggesting fixes.

This code review is for a general cleanup pass on PeriodicTask_lock
and some of the surrounding code. This is a targeted review in that
I would like to hear from three groups of people:

1) The author and reviewers for:

    JDK-7127792 Add the ability to change an existing PeriodicTask's
                execution interval

    Rickard, David H, and Markus G.

2) The reviewers for:

    JDK-8047720 Xprof hangs on Solaris

    Markus G and Coleen

3) Alex and Carsten


Here's the webrev URL:

http://cr.openjdk.java.net/~dcubed/8072439-webrev/0-for_jdk9_hs_rt/

I've attached the original RFR for JDK-8047720 that explains
the original deadlock that was being fixed. Similar testing
will be done with this fix.

Dan
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Subject: RFR (XS) fix for a safepoint deadlock (8047720)
Date: Fri, 27 Jun 2014 10:18:17 -0600
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