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

[Roger Riggs]

Hi Chris,

On 2/1/2016 11:47 AM, Chris Hegarty wrote:
> Thank you for taking this on Roger.
>
> An initial question to help my understanding. [ I think I need to
> understand this, before I can comment further on the API ]
>
> I'm a little confused about how the default handler is supposed to
> work, so I looked at the implementation and become even more confused.
> The consumer is registered on a per instance basis, and the instance
> is added to the static map when it is created. So it appears that the
> registered handler is not dependent on when the last register() is
> called, but when the last instance of a Signal for a specific signal
> is created. Is this intended?
The Signal instance delegates to a singleton SignalImpl instance
(based on the name/number).  I chose to delegate from Signal
to SignalImpl to be able to put SignalImpl in a separate package that
could be exported to the implementation of sun.misc.Signal as needed.
Otherwise, java.util.Signal would only be able to export only its public 
interface
and s.m.Signal needs more functions to be available.

The current and default consumers are stored in the singleton SignalImpl 
objects
that are used for the dispatch and calling of the consumer.

The SignalImpl instances are create on first use.  Each call to register
re-registers the SignalImpl with the VM to ensure it will be the current 
handler.

Roger


>
> -Chris.
>
> On 01/02/16 16:02, Roger Riggs wrote:
>> 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
>>
>>