Cross-platform Multithreading

Thanks After nearly two days of study, the socket communication mechanism of beej's socket tutorial is probably well understood. I found that multithreading is inevitable for better understanding of socket communication, especially P2P communication.
I am missing a cross-platform multi-threaded class! Write by yourself? Or is it free? Let's look for the "multithreading" document in Linux.
I heard that there is no thread concept in Linux, and its multithreading is simulated by processes! Is that true?

Find a convenient cross-platform multi-threaded template class. Very easy to use !!
Http://www.codeproject.com/threads/thread_class.asp#xx668326xx