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

[Marcus Larsson]

Hi Lois,

Thanks for reviewing. Replies in-line.


On 2018-02-26 17:10, Lois Foltan wrote:
> 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 wasn't a bug before, just an assumption that the stream would 
contain only a single line. With this change, the stream might contain 
multiple lines, and I want to log each of those lines as separate 
messages (so that each line is decorated).

>   There doesn't seem to be code to protect one from walking off the 
> end of errbuf?

It should be safe. The stringStream will NUL-terminate whatever is in 
the buffer, and strchr won't look past the terminating NUL. I'll add an 
assert to clarify, and guard against overflows.

>
> 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

Indeed, fixed!

>
> 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.

I'll add some comments.

Thanks,
Marcus