On Tue, Apr 23, 2002 at 06:51:42AM +0530, Sridhar N wrote:
> On Monday 22 April 2002 05:02 am, Erik Mouw wrote:
> > > If one userspace thread is doing a system call and is pre-empted, can
> > > the process execute another of its own thread that also executes a
> > > system call ?
> >
> > Sure, why not? Threads and processes are almost the same on linux, so
> > if a process can be preempted, a thread can also be preempted.
>
> Sorry, i suppose i didn't say it right. I wasn't talking about the threads
> that you create using a system call ( eg. clone() ), but i was referring to
> user-space libs ( like pthread,etc, )
AFAIK pthread DOES call clone. Most of the libraries does, because it's
easier and more reliable. The pure user-space thread libraries are often
cooperative, so they can't. When they preempt (using a signal), the
signal delivery is either delayed after the syscall returns, or the
syscall is failed (with ERESTARTSYS) andautomatically restarted IF the
handler returns with return. However I don't know the actual stack
layout so I'm not sure it will work if you switch the stacks (it seems
everything is done on user-mode stack, so it should).
--------------------------------------------------------------------------------
- Jan Hudec `Bulb' <bulb@ucw.cz>
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