From: "Peter Wächtler" <pwaechtler@loewe-komp.de>
To: Martin Wirth <martin.wirth@dlr.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Futexes IV (Fast Lightweight Userspace Semaphores)
Date: Fri, 15 Mar 2002 17:23:33 +0100 [thread overview]
Message-ID: <3C922005.50608@loewe-komp.de> (raw)
In-Reply-To: <E16lmBj-0003v4-00@wagner.rustcorp.com.au> <3C91B3A1.7030709@dlr.de>
Martin Wirth wrote:
>
> Rusty Russell wrote:
>
>>
>> Discussions with Ulrich have reaffirmed my opinion that pthreads are
>> crap. Hence I'm not all that tempted to warp the (nice, clean,
>> usable) futex code too far to meet pthreads' wierd needs.
>>
> Crap or not, there are tons of software based on pthreads and at least
> the NGPT team says that Linus
> agreed to implement for necessary kernel-infrastructure for a full, fast
> pthread implementation.
>
> Now, if you want to implement mutexes and condition variables with the
> attribute
> PTHREAD_PROCESS_SHARED then you need some functionality like the futexes.
> Or NGPT will add his own syscalls to handle these things, which is simply
> unnecessary double functionality.
>
I think the "crap" refers to current missing meatures of linuxthreads
(most notable: PTHREAD_PROCESS_SHARED on cond and mutex, don't know about sema)
BTW, NGPT introduces two new syscalls: gettid and tkill
>>
>> However, it's not too hard to implement condition variables using an
>> unavailable mutex, if we go for "full" semaphores: ie. not just
>> mutexes. It requires a bit more of a stretch for kernel atomic ops...
>>
> A full semaphore is nice, but not a full replacement for a waitqueue (or
> a pthread condition variable brr..).
> For the semaphore you always have to assure that the ups and downs are
> balanced, what is not the case
> for the condition variable.
>
also remember pthread_cond_broadcast - waking up _all_ waiting threads.
If the woken up threads check their condition and go to sleep again, is
up to them ( read: the standard mandates that _all_ get woken up)
pthread_cond_signal notifies _one_ thread - which one depends on implementation
( I would like to see a priority based decision )
next prev parent reply other threads:[~2002-03-15 16:24 UTC|newest]
Thread overview: 84+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-03-13 9:12 [PATCH] Futexes IV (Fast Lightweight Userspace Semaphores) Martin Wirth
2002-03-13 19:41 ` Bill Davidsen
2002-03-13 19:52 ` Dave McCracken
2002-03-13 22:17 ` Bill Davidsen
2002-03-13 20:06 ` Alan Cox
2002-03-15 7:31 ` Rusty Russell
2002-03-15 8:41 ` Martin Wirth
2002-03-15 15:29 ` Hubertus Franke
2002-03-15 16:23 ` Peter Wächtler [this message]
2002-03-16 0:12 ` Rusty Russell
2002-03-16 11:23 ` Martin Wirth
2002-03-18 0:52 ` Ulrich Drepper
2002-03-19 3:28 ` Rusty Russell
2002-03-19 4:05 ` Ulrich Drepper
2002-03-20 6:20 ` Rusty Russell
2002-03-20 10:42 ` Peter Wächtler
2002-03-20 17:20 ` Ulrich Drepper
2002-03-19 8:34 ` Martin Wirth
2002-03-20 6:45 ` Rusty Russell
2002-03-21 6:48 ` Martin Wirth
2002-03-24 18:25 ` Peter Wächtler
2002-03-25 2:28 ` Rusty Russell
2002-03-25 4:46 ` Rusty Russell
2002-03-25 11:56 ` Peter Wächtler
2002-03-26 1:02 ` Rusty Russell
2002-03-26 8:17 ` Martin Wirth
2002-03-26 23:10 ` Rusty Russell
2002-03-27 21:05 ` Hubertus Franke
2002-03-27 23:53 ` Rusty Russell
2002-03-25 9:47 ` Peter Wächtler
2002-03-16 19:48 ` Peter Wächtler
2002-03-17 6:50 ` Rusty Russell
-- strict thread matches above, loose matches on Subject: below --
2002-03-05 7:01 Rusty Russell
2002-03-05 22:39 ` Davide Libenzi
2002-03-05 23:16 ` Hubertus Franke
2002-03-05 23:26 ` Davide Libenzi
2002-03-05 23:37 ` Peter Svensson
2002-03-05 23:50 ` Davide Libenzi
2002-03-08 0:07 ` Richard Henderson
2002-03-06 1:46 ` Rusty Russell
2002-03-06 2:03 ` Davide Libenzi
2002-03-08 18:07 ` Linus Torvalds
2002-03-08 19:03 ` Hubertus Franke
2002-03-08 19:22 ` Linus Torvalds
2002-03-08 20:29 ` Hubertus Franke
2002-03-08 20:48 ` Matthew Kirkwood
2002-03-08 21:02 ` Linus Torvalds
2002-03-08 23:15 ` Hubertus Franke
2002-03-08 23:36 ` Alan Cox
2002-03-08 23:41 ` Linus Torvalds
2002-03-08 23:56 ` Hubertus Franke
2002-03-09 2:12 ` Linus Torvalds
2002-03-11 14:14 ` Hubertus Franke
2002-03-09 0:03 ` H. Peter Anvin
2002-03-09 1:15 ` Alan Cox
2002-03-10 19:41 ` Linus Torvalds
2002-03-11 20:49 ` Pavel Machek
2002-03-10 19:58 ` Martin J. Bligh
2002-03-10 20:40 ` Alan Cox
2002-03-10 20:28 ` Martin J. Bligh
2002-03-10 21:05 ` Alan Cox
2002-03-13 7:40 ` Rusty Russell
2002-03-13 16:37 ` Alan Cox
2002-03-12 9:35 ` Helge Hafting
2002-03-08 20:40 ` Alan Cox
2002-03-08 20:57 ` Linus Torvalds
2002-03-08 23:43 ` H. Peter Anvin
2002-03-08 22:55 ` Hubertus Franke
2002-03-08 23:38 ` Alan Cox
2002-03-08 23:44 ` H. Peter Anvin
2002-03-08 20:47 ` george anzinger
2002-03-08 23:02 ` Hubertus Franke
2002-03-08 23:47 ` george anzinger
2002-03-09 1:11 ` Alan Cox
2002-03-09 1:20 ` Linus Torvalds
2002-03-09 4:49 ` Rusty Russell
2002-03-11 22:45 ` Linus Torvalds
2002-03-11 23:12 ` Hubertus Franke
2002-03-12 7:20 ` Rusty Russell
2002-03-12 14:56 ` Hubertus Franke
2002-03-13 4:02 ` Rusty Russell
2002-03-12 17:17 ` Linus Torvalds
2002-03-13 2:57 ` Rusty Russell
2002-03-09 4:51 ` Rusty Russell
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