I just found this <a href="http://sources.redhat.com/pthreads-win32/index.html">link to Win32 PThreads</a> and wanted to know if FPC uses pthreads in the Windows implementation.

No. FPC is in general totally independant of any Unix lib on Windows. The parts that _can_ be used are typically mingw implementations of libs with little other dependancies.

It would probably ease use.

Actually it wouldn't be pretty pointless. FPC threading is modelled after Delphi, which is closer to Windows than to pthreads.

The main inconvenience to this library is that it wants to use a dll and the nice thing about FPC is "no dependencies". So maybe an interface to the C library would have to be written

What would be the need for this? Deep integration with cygwin?