[mkgmap-dev] logging improvements

Fri Mar 19 23:52:14 GMT 2021

Dear all,

Please find attached a first stab at improving the way error and other
messages are written, which at present is an ad hoc mixture of writing to
stderr, stdout and using Java logging, with no apparent logical structure.
Writing to stderr or stdout is not thread safe and causes problems when
max_jobs is greater than 1. When stderr is redirected to a file and threads
simultaneously attempt to write to it, you end up with extra numbered log
files containing a few lines that you would expect to be in the named log
file. As mkgmap supports a configuration file that defines how messages
should be logged, it doesn't make much sense writing a significant number of
messages to stderr which is not under logging control.

There are several diagnostic options that write their output using warning
as the severity, but as this is not enabled by default in the logging, they
appear to do nothing unless a logging configuration file is also used, which
is not intuitive. The --check-routing-island-len option seems somewhat
confused as it attempts to combine both reporting and fixing depending on
the value supplied. It also requires info level of logging which would
include a lot of other not necessarily wanted messages. If you are using it
to fix, you don't necessarily also want any messages.

In my view the way messages should be handled is as follows:

If the message is an informational message about the program itself and is
unrelated to processing any data then write it to stdout - this would apply
to the output of --version and --help.
If the message is an error message about an invalid parameter in the command
line, write it to stderr.
Once the command line has been processed sufficiently that a file is to be
processed then write messages using logging.
If a diagnostic option is enabled, the program should automatically log the
requested diagnostic messages. This would apply to --check-roundabouts,
--check-roundabout-flares, --report-similar-arcs, --check-routing-island-len
and --report-dead-ends.

The attached patch enhances the existing logging interface by providing the
following:
A mechanism for writing messages without any formatting getting added and
that always get written whatever level of logging is enabled.
A mechanism for writing stack trace information to the log file (I don't
believe stack traces really have any place in released code but have not
attempted to replace any of these).
Mostly directs messages as per my above proposal, though there is the
occasional place where the best option is not quite obvious to me, as I
think some of the code is not part of the main mkgmap program (there are
several main functions and some of the code is for testing purposes).
Only logs the start and finish times if files are being processed.
Outputs requested diagnostic messages regardless of enabled logging levels
Changes --report-dead-ends to be off by default, with the value of 1 being
the default if --report-dead-ends is specified without a value.
Filters duplicated --report-similar-arcs messages and ignores synthesised
arcs so that it can be used together with --make-opposite-cycleways.
Deprecates --check-routing-island-len, replacing it with
--report-routing-islands to handle reporting and --max-routing-island-len to
handle fixing.

I expect there will be the odd place where others may disagree with the
logging level for a message, but no doubt we can come to a consensus.
The patch touches quite a few source files, but there are only a few changes
that are anything more than altering the message outputting mechanism. There
is no change to any map outputs.

Cheers,
Mike

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