High Quality Content by WIKIPEDIA articles! POSIX Threads, or Pthreads, is a POSIX standard for threads. The standard, POSIX.1c, Threads extensions, defines an API for creating and manipulating threads. Implementations of the API are available on many Unix-like POSIX systems such as FreeBSD, NetBSD, GNU/Linux, Mac OS X and Solaris, but Microsoft Windows implementations also exist. For example, the pthreads-w32 is available and supports a subset of the Pthread API for the Windows 32-bit platform. Pthreads defines a set of C programming language types, functions and constants. It is implemented with a pthread.h header and a thread library.Pthreads defines a set of C programming language types, functions and constants. It is implemented with a pthread.h header and a thread library.