Is Pthread library actually a user thread solution?

@paulsm4 I am doubtful about your comment that kernel knows every thing. In this particular context of user level threads, the kernel is unaware of the fact that such a thing is happening. A user level thread's scheduling is maintained by the user himself (via the interface provided by a library) and the kernel ends up allotting just a single kernel thread to the whole process. Kernel would treat the process as a single threaded and any blocking call by one of the threads would end up blocking all the threads of that process. Refer to http://www.personal.kent.edu/~rmuhamma/OpSystems/Myos/threads.htm

In Linux, pthread is implemented as a lightweight process. Kernel (v2.6+) is actually implemented with NPTL. Let me quote the wiki content:

NPTL is a so-called 1×1 threads library, in that threads created by the user (via the pthread_create() library function) are in 1-1 correspondence with schedulable entities in the kernel (tasks, in the Linux case). This is the simplest possible threading implementation.

So pthread in linux kernel is actually implemented as kernel thread.

pthreads, per se, isn't really a threading library. pthreads is the interface which a specific threading library implements, using the concurrency resources available on that platform. So there's a pthreads implementation on linux, on bsd, on solaris, etc., and while the interface (the header files and the meaning of the calls) is the same, the implementation of each is different.

So what pthread_create actually does, in terms of kernel thread objects, varies between OSes and pthread library implementations. At a first approximation, you don't need to know (that's stuff that the pthread abstraction allows you to not need to know about). Eventually you might need to see "behind the curtain", but for most pthread users that's not necessary.

If you want to know what a /specific/ pthread implementation does, on a specific OS, you'll need to clarify your question. What Solaris and Linux do, for example, is very different.