Improve registering signal handlers in java.lang.Terminator.setup()

[Neil Richards]

On Wed, 2012-08-08 at 13:28 +0100, Alan Bateman wrote:
> On 07/08/2012 19:07, Neil Richards wrote:
> > :
> > Digging back into its history, I see that it all stems from running java
> > under 'nohup' (e.g. 'nohup java ProgramWithShutdownHooks&').
> >
> > 'nohup' prevents things being registered against SIGHUP, so trying to do
> > so causes an exception to be thrown.
> >
> > When this happens, the Terminator code currently decides that it
> > shouldn't bother trying to register shutdown hooks for SIGINT or SIGTERM
> > either.
> >
> > The result is that shutdown hooks aren't currently run when a java
> > process run using 'nohup' is sent a SIGINT or SIGTERM signal, because of
> > the code's (false) assumption that a failure to register a handler for
> > SIGHUP must mean that the VM is running in -Xrs mode.
> >
> > I don't think the current observed behaviour in this scenario is either
> > expected or desirable.
> > It occurs for both J9 and Hotspot (at least, on my Ubuntu box, bash
> > shell).
> >
> > Hope this helps to clarify the scenario.
> >
> Thanks for helping to clarify what this issue is about. One thing that 
> still isn't clear (to me anyway) is whether IAE is really thrown in this 
> case. I did a quick test on Ubuntu 12.04:
> 
> $ nohup strace -f java Test 2> log &
> 
> and in the log I see the sigactions as I expected:
> 
> [pid 13829] rt_sigaction(SIGHUP, NULL, {SIG_IGN, [], 0}, 8) = 0
> [pid 13829] rt_sigaction(SIGINT, NULL, {SIG_DFL, [], 0}, 8) = 0
> [pid 13829] rt_sigaction(SIGTERM, NULL, {SIG_DFL, [], 0}, 8) = 0
> 
> So I don't think we are actually getting an IllegalArgumentException in 
> this case. Maybe you are seeing something different?
> 
> -Alan.

Hi Alan,
Apologies, I confused myself about the Hotspot behaviour.
(I was testing with 'nohup', but not checking the contents of
'nohup.out' for the output from my registered shutdown hook - doh!).

You're correct, when running with Hotspot with 'nohup', no exception is
thrown when trying to register a handler for SIGHUP.

When running with J9 with 'nohup', the VM notices that a handler
registered for SIGHUP is never going to get triggered, so throws the
exception to notify the caller (of Signal.handle( )) about this.

Regards,
Neil

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