RFR: 8190346: improve unified JVM logging help message and warnings

[Lois Foltan]

On 2/22/2018 10:34 AM, Marcus Larsson wrote:

> Hi,
>
> Please review the following patch to improve the -Xlog help and 
> warning messages.
>
> The changes include:
>
>  * Attempt to find and give suggestions for log selections that don't
>    match any tag sets. For example, when passing "-Xlog:load" issue a
>    warning similar to the following: "No tag set matches selection
>    'load'. Did you mean any of the following? load* class+load
>    module+load".
>  * Change log level for almost all startup logging on 'logging' tag
>    from trace/debug to info level. These are log messages that are only
>    printed once during startup, so it makes little sense in obscuring
>    them under debug/trace. The all tag set listing is only moved from
>    trace to debug, though.
>  * Make LogConfiguration::print_command_line_help() take an
>    outputStream* instead of FILE*, to better align it with various
>    describe/print_on functions.
>  * Add descriptions of log file output related options to -Xlog:help
>    output.
>  * Print 'none' if there are no decorations configured for an output
>    (instead of just printing nothing).
>
> Issue:
> https://bugs.openjdk.java.net/browse/JDK-8190346
>
> Webrev:
> http://cr.openjdk.java.net/~mlarsson/8190346/webrev.00
>
> Tested with hs-tier 1-2, and locally with 
> test/hotspot/jtreg/{runtime,serviceability,gc}/logging.
>
> Thanks,
> Marcus
>
Hi Marcus,
This looks good.  Couple of review comments:

hotspot/share/logging/logConfiguration.cpp:
- line #370-382 - curious to know why the need to walk the errbuf string 
looking for the next newline character?  Was there a bug present when 
just calling log_error or log_warning?    There doesn't seem to be code 
to protect one from walking off the end of errbuf?

hotspot/share/logging/logOutput.cpp
- line #90 - minor comment that the delimiter could just be of type 
'char' instead of an array?  You would have to adjust the format string 
to use %c

hotspot/share/loggin/logSelection.cpp
- LogSelection::similariy and class SimilarityComparator - can you add a 
header comment for class SimilarityComparator describing the heuristic 
used to compute the set of potentially similar -Xlog options.  That's 
what it is doing correct?  There just seems to be a lot of hard coded 
numbers is this section of new code that would be could to understand.

Thanks,
Lois