C++ multithreading logger class
Pretty good for a beginning, but I would have a lot of feature requests if I were a user.

Allow the user to provide a full file specification so that the file appears where the user expects it.
The logger should get the day and time of day and report that in each message.
The logger should be initialized with the program name so that the all the messages contain the program name, this way if multiple processes are writing to the same file one will know which process made the log entry.

Make it into a library by providing a header file and a C++ source file.