RFR 9: 8087286 Need a way to handle control-C and possibly some other signals

[Roger Riggs]

Please review an API addition to handle signals such as SIGINT, SIGHUP, 
and SIGTERM.
This JEP 260 motivated alternative to sun.misc.Signal supports the use 
case for
interactive applications that need to handle Control-C and other signals.

The new java.util.Signal class provides a settable primary signal 
handler and a default
signal handler.  The primary signal handler can be unregistered and 
handling is restored
to the default signal handler.  System initialization registers default 
signal handlers
to terminate on SIGINT, SIGHUP, and SIGTERM.  Use of the Signal API requires
a permission if a SecurityManager is set.

The sun.misc.Signal implementation is modified to be layered on a common
thread and dispatch mechanism. The VM handling of native signals is not 
affected.
The command option to reduce signal use by the runtime with -Xrs is 
unmodified.

The changes to hotspot are minimal to rename the hardcoded callback to 
the Java
Signal dispatcher.

Please review and comment on the API and implementation.

javadoc:
   http://cr.openjdk.java.net/~rriggs/signal-doc/

Webrev:
jdk:  http://cr.openjdk.java.net/~rriggs/webrev-signal-8087286/
hotspot: http://cr.openjdk.java.net/~rriggs/webrev-hs-signal-8087286/

Issue:
    https://bugs.openjdk.java.net/browse/JDK-8087286

JEP 260:
   https://bugs.openjdk.java.net/browse/JDK-8132928

Thanks, Roger