[15] RFR: 8248476: No helpful NullPointerException message after calling fillInStackTrace

[Lindenmaier, Goetz]

Hi Christoph, 

I added the case you mentioned to the test, so it's
documented that this is on-purpose.
http://cr.openjdk.java.net/~goetz/wr20/8248476-NPE_fillInStackTrace-jdk15/02/

Best regards,
  Goetz.


> -----Original Message-----
> From: Christoph Dreis <christoph.dreis at freenet.de>
> Sent: Monday, June 29, 2020 2:16 PM
> To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; hotspot-runtime-
> dev at openjdk.java.net
> Subject: Re: [15] RFR: 8248476: No helpful NullPointerException message
> after calling fillInStackTrace
> 
> Hi Goetz,
> 
> > One design principle of the new message was not
> > to introduce overhead if the message is not printed.
> > Therefore I don't want to record any additional
> > information about what happened, which I would
> > need to distinguish the cases.
> > Also, reporting a wrong message as the one you detected
> > is a no-go.
> > Thus, I prefer to skip the message in this case.
> 
> I prefer no message in this edge case, too.
> Rather have none than a wrong one.
> 
> I wanted to state the other edge-case we're knowingly "break" for
> completeness reasons, though.
> 
> > An alternative fix I could imagine would be to
> > override fillInStackTrace in NPE.java. It could
> > call getMessage() and then super.fillInStackTrace,
> > and return a new exception with the message.
> > But this would also compute the message in cases
> > where it is not printed.
> 
> That would again violate the design principle if the message is not consumed,
> I guess.
> 
> So overall I'd be fine with the patch.
> As said: This was my local approach before reporting, but I didn't want to
> break the mentioned case.
> 
> Cheers,
> Christoph
> 
> > -----Original Message-----
> > From: Christoph Dreis <christoph.dreis at freenet.de>
> > Sent: Monday, June 29, 2020 1:28 PM
> > To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; hotspot-runtime-
> > dev at openjdk.java.net
> > Subject: Re: [15] RFR: 8248476: No helpful NullPointerException message
> > after calling fillInStackTrace
> >
> > Hi Goetz,
> >
> > > If changing the stack trace by calling fillInStackTrace in user code, the
> > > NPE algorithm lacks the proper information to compute the message.
> > > Thus, we must omit it after that call.
> >
> > > I implement this by checking for a call to fillInStackTrace at the bci
> > > recorded in the exception.
> > > http://cr.openjdk.java.net/~goetz/wr20/8248476-NPE_fillInStackTrace-
> > jdk15/01/
> >
> > I tried this when reporting the issue already. The problem with this is, that
> it
> > suppresses any valid exception.
> >
> > E.g. the following example would not throw any helpful NPE anymore.
> >
> > public class Main {
> > 	public static void main(String[] args) {
> > 		NullPointerException ex = null;
> > 		ex.fillInStackTrace();
> > 	}
> > }
> >
> > Cheers,
> > Christoph
> >
> >
> 
>