Logger

[ardasener]

This PR adds a Logger class to the utils namespace.

The structure of the log messages is the following:

[TIME] [LEVEL] [SOURCE] MESSAGE

TIME is a date and time string. Note that this uses the locale so could differ from system to system.

LEVEL can be INFO or WARNING. Other levels can be easily added later if need be. Note that ERROR is not implemented as those should be exceptions instead. DEBUG is also not implemented as ideally that would be turned on/off in compile time; this could be implemented later as a separate function.

SOURCE will typically be the demangled class name however developers can customize it if needed.

Here is an example:

[10/21/22 00:10:51] [WARNING] [sparsebase::format::CSR<unsigned int, unsigned int, unsigned int>] CSR column array must be sorted. Sorting...

Developers can use the Logger as shown here:

utils::Logger logger(typeid(this));
logger.Log("COO arrays must be sorted. Sorting...", utils::LOG_LVL_WARNING);

Instead of typeid(this) the developer can also pass an arbitrary string. This is used to show the source field in the log message.

Users can adjust various aspects of the logging. Here is an example:

// Doesn't log INFO level events
utils::Logger::set_level(utils::LOG_LVL_WARNING); 

// Write to file as well as print
utils::Logger::set_file("test.log");

// Use stderr instead of stdout
utils::Logger::set_stdout(false);
utils::Logger::set_stderr(true);

[AmroAlJundi]

Have you considered using the observer pattern? This way we could add more output channels. This might be too looking ahead but this would allow us to log into a socket for example.

Each level can have its own subscribers list and it can by default by initialized to the standard ones.

[Atahanak]

I dug around and found the following, Design Patterns for logging, I believe for milestone 3 current logging ability is okay. We may need to advance it in future releases.

[ardasener]

I dug around and found the following, Design Patterns for logging, I believe for milestone 3 current logging ability is okay. We may need to advance it in future releases.

I did use chain of responsibility before for logging in another project. But here it felt overly complex. However, we can implement that later if we need to.