More flexible logging functionality

[LnnrtS]

If you asked me about the improvement to µOS++ that I would wish an update for, I'd say its the logging.

I have turned logging off completely because my applications already uses the ITM trace and I couldn't make both coexist in a reasonable manner. I see two problems with the current implementation

Log messages are too condensed

I guess this is due to performance reasons. I don't know what big of an influence the message length has vs the impact of calling into printf formatting at all. But as a developer I would kind of expect performance to decrease when having logging enabled so adding a bit of verbosity shouldn't hurt too much.

There are too little options to filter in which context a specific message should be printed or not

Right now there is only the option to enable/disable all logging for a specific type of object at compile time. In my experience this is not enough for targeted debugging. What would be great is:

• Add a level to every message (for example Error, Warning, Info, Debug, Verbose)
• Compile-time filtering by level to be omitted from the build completely
• Changing the active level at run-time (with RAII helpers that restore the previous level when they go out of scope)
• Global and per-thread level (I implemented that by extending os_thread_user_storage_t)
• Ensure consistency of log messages (I protected the formatting and sending of every message by a robust mutex but that's probably not an ideal solution)
• Use fmt for formatting (I have not used it myself but it has been added to the standard in c++20 although neither gcc not llvm seem to have integrated it yet)

I think the zephyr logging module is also worth looking at.

Would be interested in hearing your thoughts about that..

[ilg-ul]

Log messages are too condensed - I guess this is due to performance reasons

That's correct, in some places time is critical and I tried to impact performances as little as possible. But I think that this can be changed, with a configuration variable we can emit longer messages.

Error, Warning, Info, Debug, Verbose

Yes, I considered this, but had no time to implement it yet. Hopefully in the next iteration. I have no experience with Zephyr, but if you think it is worth looking at, we'll consider it.

Use fmt for formatting

Yes, that's an idea worth considering. And I guess there might be more C++20 nice features to consider.

Actually I planned a rework of the newlib stdio functions, aiming for a better integration with the C++ functions. The idea was to have some core formatting functions, to be used both in C and C++, and some years ago I did some experiments, but I had no time to review them.