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Groups > comp.unix.programmer > #712
| From | Rainer Weikusat <rweikusat@mssgmbh.com> |
|---|---|
| Newsgroups | comp.unix.programmer |
| Subject | Re: threads, signals, and atomicity of basic types |
| Date | 2011-06-02 17:54 +0100 |
| Message-ID | <87aae0dvij.fsf@sapphire.mobileactivedefense.com> (permalink) |
| References | <ygfwrh6d6yr.fsf@janus.isnogud.escape.de> <c9ab1037-b921-4f0a-adef-1f79828ab89e@y27g2000prb.googlegroups.com> <87r57ccynl.fsf@sapphire.mobileactivedefense.com> <b8e63d87-1e4c-4157-9f90-aa4af98300f6@17g2000prr.googlegroups.com> |
Joshua Maurice <joshuamaurice@gmail.com> writes:
> On Jun 2, 3:31 am, Rainer Weikusat <rweiku...@mssgmbh.com> wrote:
>> Joshua Maurice <joshuamaur...@gmail.com> writes:
>>
>> > If you're worried about inter-thread communication, volatile is
>> > useless. Do not use it. The utility of volatile for portable inter-
>> > thread communication is a urban legend which continues to be
>> > perpetuated despite the community's best attempts to kill it.
>>
>> And the general uselessness of volatile which is supposed to follow
>> from the original misunderstanding of its purpose is another urban
>> legend perpetuated by the same 'experts' who created the first one.
>
> I have not claimed that volatile is useless. I have claimed that
> volatile is useless for portable threading. Are you suggesting that as
> a matter of facts volatile is portably useful for threading?
Trivially, since the meaning of volatile is completely orthogonal to
'threading', the answer is obviously: "Yes it is" and the question
similar to 'are you suggesting that function calls are useful for
portable threading?' and the general advice "Do not use it" is
nonsense.
> This is demonstrably incorrect.
Something you (and/or , all kinds of other people) wrongly believed to
be the purpose of 'volatile' (I'm not even certain what this was
exactly supposed to be) is 'demonstrably' not its purpose. But this
doesn't mean that I share or ever shared this wrong belief.
For instance, assuming that a platform for single-word memory accesses
are atomic provided they are correctly aligned is being used and that
a compiler actually aligns them correctly (which, for all practical
purposes, means 'assuming that a computer and a C compiler are being
used') and the following code snippet
static int b;
while (!b);
printf("b is now %d\n", b);
was being executed by one thread of a multi-threaded program and some
other thread will eventually modify b, the declaration really ought to
be
static volatile int b;
in order to inform the compiler that the code above is not
semantically equivalent to
while (1);
because of 'something' (this is actually the 'volatile sig_atomic_t'
signal handler case in disguise).
[...]
>> > From my limited understanding, volatile is woefully insufficient for
>> > MMIO on all relevant platforms.
>>
>> It is the only way to inform a standards-compliant C compiler that
>> read accesses to some object produce side effects. Which they often do
>> for memory mapped device control operations, eg, reading an interrupt
>> register which resets itself upon read.
>
> As I said, it is my understanding that as a matter of fact, for most
> desktops and servers, volatile plus knowledge of the memory addresses
> is insufficient to do correct MMIO.
Yes. And on a similar note, the subtraction operator is insufficient
to write a desktop calculator program.
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threads, signals, and atomicity of basic types Urs Thuermann <urs@isnogud.escape.de> - 2011-05-31 21:07 +0200
Re: threads, signals, and atomicity of basic types Xavier Roche <xroche@free.fr.NOSPAM.invalid> - 2011-05-31 22:44 +0200
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-01 11:58 +0100
Re: threads, signals, and atomicity of basic types Xavier Roche <xroche@free.fr.NOSPAM.invalid> - 2011-06-01 14:15 +0200
Re: threads, signals, and atomicity of basic types Xavier Roche <xroche@free.fr.NOSPAM.invalid> - 2011-06-02 13:49 +0200
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-02 13:40 +0100
Re: threads, signals, and atomicity of basic types Richard Kettlewell <rjk@greenend.org.uk> - 2011-05-31 22:50 +0100
Re: threads, signals, and atomicity of basic types Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-31 21:32 -0400
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-01 12:35 +0100
Re: threads, signals, and atomicity of basic types Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-01 23:01 -0400
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-02 11:22 +0100
Re: threads, signals, and atomicity of basic types Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-02 07:52 -0400
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-02 13:38 +0100
Re: threads, signals, and atomicity of basic types Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-02 21:27 -0400
Re: threads, signals, and atomicity of basic types David Schwartz <davids@webmaster.com> - 2011-06-01 12:55 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-01 22:54 +0100
Re: threads, signals, and atomicity of basic types Alex Fraser <me@privacy.net> - 2011-06-02 21:00 +0100
Re: threads, signals, and atomicity of basic types David Schwartz <davids@webmaster.com> - 2011-06-04 21:53 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-05 16:39 +0100
Re: threads, signals, and atomicity of basic types David Schwartz <davids@webmaster.com> - 2011-06-06 18:48 -0700
Re: threads, signals, and atomicity of basic types Nobody <nobody@nowhere.com> - 2011-06-07 06:50 +0100
Re: threads, signals, and atomicity of basic types David Schwartz <davids@webmaster.com> - 2011-06-07 06:04 -0700
Re: threads, signals, and atomicity of basic types Nobody <nobody@nowhere.com> - 2011-06-07 22:48 +0100
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-07 23:18 +0100
Re: threads, signals, and atomicity of basic types gordonb.lhpq6@burditt.org (Gordon Burditt) - 2011-06-07 18:28 -0500
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-08 11:09 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-08 14:32 -0700
Re: threads, signals, and atomicity of basic types David Schwartz <davids@webmaster.com> - 2011-06-09 18:10 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-10 15:26 +0100
Re: threads, signals, and atomicity of basic types James Waldby <not@valid.invalid> - 2011-06-10 16:49 +0000
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-10 19:07 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-10 13:13 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-07 12:55 +0100
Re: threads, signals, and atomicity of basic types David Schwartz <davids@webmaster.com> - 2011-06-07 06:02 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-07 16:05 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-07 13:37 -0700
Re: threads, signals, and atomicity of basic types scott@slp53.sl.home (Scott Lurndal) - 2011-06-14 21:43 +0000
Re: threads, signals, and atomicity of basic types Nobody <nobody@nowhere.com> - 2011-06-15 03:07 +0100
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-15 10:22 +0100
Re: threads, signals, and atomicity of basic types Casper H.S. Dik <Casper.Dik@OrSPaMcle.COM> - 2011-06-15 09:40 +0000
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-15 13:20 +0100
Re: threads, signals, and atomicity of basic types Casper H.S. Dik <Casper.Dik@OrSPaMcle.COM> - 2011-06-15 13:19 +0000
Re: threads, signals, and atomicity of basic types Nobody <nobody@nowhere.com> - 2011-06-15 17:41 +0100
Re: threads, signals, and atomicity of basic types David Schwartz <davids@webmaster.com> - 2011-06-15 20:20 -0700
Re: threads, signals, and atomicity of basic types Nobody <nobody@nowhere.com> - 2011-06-15 17:31 +0100
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-15 18:31 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-15 13:32 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-15 22:19 +0100
Re: threads, signals, and atomicity of basic types Nobody <nobody@nowhere.com> - 2011-06-16 05:02 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-14 23:23 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-15 10:12 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-15 02:53 -0700
Re: threads, signals, and atomicity of basic types David Schwartz <davids@webmaster.com> - 2011-06-08 10:19 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-10 16:50 +0100
Re: threads, signals, and atomicity of basic types David Schwartz <davids@webmaster.com> - 2011-06-15 20:24 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-16 22:11 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-17 04:43 -0700
Re: threads, signals, and atomicity of basic types Michael Press <rubrum@pacbell.net> - 2011-06-19 01:43 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-19 13:35 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-19 17:06 -0700
Re: threads, signals, and atomicity of basic types scott@slp53.sl.home (Scott Lurndal) - 2011-06-20 16:22 +0000
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-20 19:16 +0100
Re: threads, signals, and atomicity of basic types scott@slp53.sl.home (Scott Lurndal) - 2011-06-21 17:30 +0000
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-21 13:02 -0700
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-20 14:32 -0700
Re: threads, signals, and atomicity of basic types scott@slp53.sl.home (Scott Lurndal) - 2011-06-21 17:05 +0000
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-19 17:01 -0700
Re: threads, signals, and atomicity of basic types Michael Press <rubrum@pacbell.net> - 2011-06-22 01:55 -0700
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-22 03:36 -0700
Re: threads, signals, and atomicity of basic types David Schwartz <davids@webmaster.com> - 2011-06-02 21:53 -0700
Re: threads, signals, and atomicity of basic types David Schwartz <davids@webmaster.com> - 2011-06-03 04:24 -0700
Re: threads, signals, and atomicity of basic types Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-03 07:52 -0400
Re: threads, signals, and atomicity of basic types "Ersek, Laszlo" <lacos@caesar.elte.hu> - 2011-06-02 00:23 +0200
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-01 20:11 -0700
Re: threads, signals, and atomicity of basic types "Ersek, Laszlo" <lacos@caesar.elte.hu> - 2011-06-02 22:54 +0200
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-02 14:03 -0700
Re: threads, signals, and atomicity of basic types "Ersek, Laszlo" <lacos@caesar.elte.hu> - 2011-06-03 02:49 +0200
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-02 17:54 -0700
Re: threads, signals, and atomicity of basic types Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-02 21:36 -0400
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-03 16:25 +0100
Re: threads, signals, and atomicity of basic types "Ersek, Laszlo" <lacos@caesar.elte.hu> - 2011-06-03 03:12 +0200
Re: threads, signals, and atomicity of basic types "Ersek, Laszlo" <lacos@caesar.elte.hu> - 2011-06-02 00:45 +0200
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-02 11:26 +0100
Re: threads, signals, and atomicity of basic types Alex Fraser <me@privacy.net> - 2011-06-02 21:05 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-01 20:21 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-02 11:31 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-02 09:12 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-02 17:54 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-02 14:00 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-03 15:19 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-03 15:50 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-05 16:46 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-05 15:28 -0700
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-06 13:35 +0100
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-06 09:19 -0700
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-06 09:26 -0700
Re: threads, signals, and atomicity of basic types Ian Collins <ian-news@hotmail.com> - 2011-06-07 09:43 +1200
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-07 13:29 +0100
Re: threads, signals, and atomicity of basic types Ian Collins <ian-news@hotmail.com> - 2011-06-08 09:04 +1200
Re: threads, signals, and atomicity of basic types Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-06-08 12:34 +0100
Re: threads, signals, and atomicity of basic types Ian Collins <ian-news@hotmail.com> - 2011-06-09 07:37 +1200
Re: threads, signals, and atomicity of basic types Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-07 14:55 -0700
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