Does POSIX Pthreads run in user space or kernel space?

[unregistered]

as above?

[kbw]

If the system has kernel support for threads, yes.

[jsmith]

I don't understand the question.

User threads always run in user space regardless of implementation.

The question might really be: is context switching amongst threads
implemented in user space or kernel-assisted. The answer to that
for Linux at least is kernel-assisted. (for both linux-threads and NPTL)

[unregistered]

sorry but I'm a beginner to threads
err so Pthreads are user threads?
What I read was that for user threads, the thread management is faster than with kernel threads but since the kernel might not be aware that there are user threads in a process, a single thread that blocks due to waiting for some IO,etc might block the entire process and I was wondering if this problem exists when using the POSIX pthread.h library

[jsmith]

The problem will not exist with pthreads.

[unregistered]

What is the reason behind that the problem is not present with the usage of pthreads?

[jsmith]

All pthreads libraries I am aware of (linux threads, NPTL) use kernel-assisted context switching.