The SILC Scheduler is the heart of any application. The scheduler provides
 the application's main loop that can handle incoming data, outgoing data,
 timeouts and dispatch different kind of tasks.

 The SILC Scheduler supports file descriptor based tasks and timeout tasks.
 File descriptor tasks are tasks that perform some operation over the
 specified file descriptor. These include network connections, for example.
 The timeout tasks are timeouts that are executed after the specified
 timeout has elapsed.

 The SILC Scheduler is designed to be the sole main loop of the application
 so that the application does not need any other main loop.  However,
 SILC Scheduler does support running the scheduler only once, so that the
 scheduler does not block, and thus providing a possiblity that some
 external main loop is run over the SILC Scheduler.

 Typical application first initializes the scheduler and then registers
 the very first tasks to the scheduler and then run the scheduler.  After
 the scheduler's run function returns the application is considered to be
 ended.

 On WIN32 systems the SILC Scheduler is too designed to work as the main
 loop of the GUI application. It can handle all Windows messages and
 it dispatches them from the scheduler, and thus makes it possible to
 create GUI applications. The scheduler can also handle all kinds of
 WIN32 handles, this includes sockets created by the SILC Net API routines,
 WSAEVENT handle objects created by Winsock2 routines and arbitrary
 WIN32 HANDLE objects.

 The SILC Scheduler supports multi-threads as well. The actual scheduler
 must be run in single-thread but other threads may register new tasks
 and unregister old tasks.  However, it is enforced that the actual
 task is always run in the main thread.  The scheduler is context based
 which makes it possible to allocate several schedulers for one application.
 Since the scheduler must be run in single-thread, a multi-threaded
 application could be created by allocating own scheduler for each of the
 worker threads.