Re: kerel level threads

[Glynn Clements <glynn@gclements.plus.com>]

Glynn Clements wrote:

> >     Point me to appropiate group if this question doesnt fit here.
> >     Does pthread_create() create kernel level threads?
> >     I have created two threads A and B. Thread A was written to print 
> > some statement in an infinite loop, while Thread B was written to be 
> > blocked for some time(I have used sleep system call to block Thread B). 
> > If at all pthread_create() creates user level threads, Blocking of 
> > Thread B will also make Thread A to be blocked.  But  in my output, 
> > Thread A was continously printing even when Thread B was blocked.  My 
> > observation is that either both of the threads be Kernel level threads 
> > or pthread library has given wrapper functions for blocking calls(for 
> > example, sleep system call in our case) which stop all of the threads to 
> > be blocked.  I read in text books that pthread libray is for creating 
> > user level threads(threads about which kernel is not aware of).
> 
> libpthread creates kernel threads.

By which I mean that the kernel creates additional "tasks" using
clone(). The new tasks have their own kernel-level data (signal masks
etc) and are scheduled by the kernel.

There are threading libraries which don't require any support from the
kernel, but are implemented entirely in user-space. That isn't how the
pthread library is implemented.

On Linux, the term "kernel thread" can also refer to threads which
execute entirely within the kernel. The pthread library doesn't have
anything to do with those.

-- 
Glynn Clements <glynn@gclements.plus.com>