UL question: combining output flags with or at code site?

[Thomas Stüfe]

Thank you, Stefan. For the moment a helper function may be the simplest
solution.

Maybe long-term we could have a LogTarget variant OR-combining the flags
instead of AND-ing them...

Sometimes I think I would have prepared ORing the flags by default, I would
have found that less surprising and easier to use (e.g. if I find a
particular "gc" log output useful, I could have added a "metaspace" tag and
thus selected it for -Xlog=metaspace too. As it is now, this would just
effectively mute the output by requiring both flags to be set).

Alas, it is now what it is, and its a matter of taste anyway...

Thanks, Thomas



On Thu, Apr 23, 2020 at 9:33 AM Stefan Karlsson <stefan.karlsson at oracle.com>
wrote:

> Hi Thomas,
>
> On 2020-04-23 06:45, Thomas Stüfe wrote:
> > Hi,
> >
> > with UL, is there a way at the logging site to specify that a logging has
> > to happen if one of the flags is set (so, *or* combined)?
> >
> > E.g. if I wanted to print something when either "cds" or "metaspace" is
> > active? Without forcing the user to specify an asterix at the -Xlog
> > command, because that would activate too many other output sites.
> >
> > If I use it like this:
> >
> > LogTarget(Info, cds, metaspace) lt;
> >
> > both flags must be active to print the output, right?
>
> You can use the type-erasure feature of the LogTargetHandle.
>
>    LogTarget(Info, cds) log_cds;
>    LogTarget(Info, metaspace) log_metaspace;
>
>    LogTargetHandle log_handle_cds(log_cds);
>    LogTargetHandle log_handle_metaspace(log_metaspace);
>
>    LogTargetHandle log(log_cds.is_enabled() ? log_handle_cds :
> log_handle_metaspace);
>
>    log.print("Either cds or metaspace");
>
> With the above you get:
>
> $ java -Xlog:cds -XX:+UseZGC -version
> [0.015s][info][cds] Either cds or metaspace
>
> $ java -Xlog:metaspace -XX:+UseZGC -version
> [0.015s][info][metaspace] Either cds or metaspace
>
> $ java -Xlog:metaspace,cds -XX:+UseZGC -version
> [0.015s][info][cds] Either cds or metaspace
>
> And nothing if you don't specify either:
> $ java -XX:+UseZGC -version
>
> You could also use a third LogTarget/LogTargetHandle to specify the
> combination of cds+metaspace and use that as a combination above.
>
> Maybe there's a way to shrink this down. It would have been nice to be
> able to write:
>
> LogTargetHandle log(log_cds.is_enabled() ? log_cds.handle() :
> log_metaspace.handle());
>
> Or you could create a helper function to hide it:
> LogTargetHandle log = cds_or_metaspace_logger();
>
> HTH,
> StefanK
>
> >
> > Thanks, Thomas
> >
>