Date: Mon, 31 Jul 2000 10:11:27 +0200 From: Bjorn Tornqvist <bjorn@tornqvist.net> To: chris@calldei.com Cc: Nate Williams <nate@yogotech.com>, freebsd-hackers@freebsd.org Subject: Re: BSD,Posix,Linux Threading - Are they really useable? Message-ID: <398534AF.467DE4D5@tornqvist.net> References: <398111DA.443B41F9@tornqvist.net> <20000728003913.K37935@holly.calldei.com> <200007281538.JAA22915@nomad.yogotech.com> <20000728140854.L37935@holly.calldei.com>
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Chris Costello wrote:
>
> On Friday, July 28, 2000, Nate Williams wrote:
> > > That is incorrect. FreeBSD's userland pthread implementation
> > > does not block the whole process on I/O. POSIX does not specify
> > > this behavior either.
>
> > Actually, sometimes it does (for example when reading from an I/O device
> > where select can't be used succesfully).
>
> Hmm. That's true. And that's where uthreads has its main
> problems as I understand it.
>
...which is what I need to avoid. (Chris: Sorry for any confusion
earlier on; When I replied to you I reran the testprogram which then
used intermediate files instead of pipes - thus pthreads seems to work
fine).
But how do I know if my pthreads aren't secretely blocking for a very
short time in read() and write()? Documentation anywere?
> > > > FreeBSD Kernel-threads (dunno what they are called actually) can't be
> > > > used natively!? (Searched the archives and found an explanation that the
> > > > only way to access normal kernel SMP-thread functionality is to use
> > > > LinuxThreads)
>
> > > FreeBSD's kernel threads are for separate threads of execution
> > > in the kernel and aren't the same thing as threads for a user
> > > process.
>
> > You're missing the point. He's asking for 'kernel threads' so that
> > multiple independant thread of execution for a given 'userland process'
> > can be running simulataneously (virtually on a UP, and realistically on
> > a MP).
>
> I thought he had seen the term 'kernel threads' in the context
> of FreeBSD before, likely in the context of kthread_create() in
> the kernel.
Actually I have, but I haven't tried them since I found no documentation
on them (I even emailed peter@freebsd.org (he's listed as maintainer in
sys/kthread.h) but got no reply). Just aswell, seeing how wrong I was.
I think I'll stick to pthreads for now; which will make it easier to
modify the code later on when we have ''real'' threads. (Sorry, I come
from a BeOS background).
Another question for you all: Does FreeBSD have any notion of kernel
mutexes and/or semaphores (that can be used to control concurrent
processes), and that can be shared between processes using pthreads?
pthread_mutex_init is local to a process and thus of little use. (FYI:
The application my company is developing consists of several processes,
all of which must have a couple of worker threads).
TIA,
Bjorn
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