Question

The title might not be clear enough because I don’t know how to define my questions actually.

I understand Pthread is a thread library meeting POSIX standard (about POSIX, see wikipedia: http://en.wikipedia.org/wiki/Posix). It is available in Unix-like OS.

About thread, I read that there are three different models:

User level thread: the kernel does not know it. User himself creates/implements/destroy threads.

Kernel level thread: kernel directly supports multiple threads of control in a process.

Light weight process(LWP): scheduled by kernel but can be bounded with user threads.

Did you see my confusion? When I call pthread_create() to create a thread, did I create a user level thread? I guess so. So can I say, Pthread offers a user level solution for threads? It can not manipulate kernel/LWP?

Answer 1

I understand Pthread is a thread library meeting POSIX standard

Yes. Actually, "Pthreads" stands for "Posix threads":
http://en.wikipedia.org/wiki/Pthreads

It is available in Unix-like OS.

Actually, it’s available for many different OSs … including Windows, MacOS … and, of course, Linux, BSD and Solaris.

About thread, I read that there are three different models

Now you’re getting fuzzy. "Threads" is a very generic term. There are many, many different models. And many, many different ways you can characterize and/or implement "threads". Including stuff like the Java threading model, or the Ada threading model.

When I call pthread_create() to create a thread, did I create a
user level thread?

Yes: Just about everything you do in user space is "protected" in your own, private "user space".

User level thread: the kernel does not know it.

No. The kernel knows everything 🙂

Kernel level thread: kernel directly supports multiple threads of
control in a process.

Yes, there is such a thing as "kernel threads".

And, as it happens, Linux makes EXTENSIVE use of kernel threads. For example, every single process in a Linux system is a "kernel thread". And every user-created pthread is ALSO implemented as a new "kernel thread". As are "worker threads" (which are completely invisible to any user-level process).

But this is an advanced topic you do NOT need to understand in order to effectively use pthreads. Here’s a great book that discussed this – and many other topics – in detail:

Linux Kernel Development, Robert Love

Remember: "Pthreads" is an interface. How it’s implemented depends on the platform. Linux uses kernel threads; Windows uses Win32 threads, etc.

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Addendum

Since people still seem to be hitting this old thread, I thought it would be useful to reference this post:

https://stackoverflow.com/a/11255174/421195

Linux typically uses two implementations of pthreads:
LinuxThreads and Native
POSIX Thread Library(NPTL),
although the former is largely obsolete. Kernel from 2.6 provides
NPTL, which provides much closer conformance to SUSv3, and perform
better especially when there are many threads.

You can query the
specific implementation of pthreads under shell using command:

getconf GNU_LIBPTHREAD_VERSION

You can also get a more detailed implementation difference in The
Linux Programming Interface.

"Pthreads" is a library, based on the Posix standard. How a pthreads library is implemented will differ from platform to platform and library to library.