* [9fans] non-interruptible temporary: why do we care?
@ 2021-01-04 3:32 ori
2021-06-16 20:23 ` unobe
0 siblings, 1 reply; 10+ messages in thread
From: ori @ 2021-01-04 3:32 UTC (permalink / raw)
To: 9fans
Our compilers will sometimes produce a warning about
a non-interruptible temporary:
#include <u.h>
#include <libc.h>
void
f(vlong a)
{
vlong x, y, z;
x = y = z = a;
}
cpu% 5c -w test.c
warning: /fd/0:7 non-interruptable temporary
warning: /fd/0:7 non-interruptable temporary
I know this means that the intermediate values
cannot be assigned atomically, but I don't see
why this rates a warning. From what I understand,
the uninterruptability of the temporaries should
be unobservable as long as our note handlers
save and restore registers correctly.
The only case I can think of is that a note
handler may see "tearing" of a register, but
that doesn't require a non-interruptible
temporary -- this kind of code will suffice:
vlong x;
int
use_x(){ return x; }
void
main(void)
{
atnotify(use_x, 1);
while(1)
x++;
}
Why do we warn about non-interruptible
temporaries? What issues am I missing?
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* Re: [9fans] non-interruptible temporary: why do we care?
2021-01-04 3:32 [9fans] non-interruptible temporary: why do we care? ori
@ 2021-06-16 20:23 ` unobe
2021-06-16 20:28 ` ori
` (2 more replies)
0 siblings, 3 replies; 10+ messages in thread
From: unobe @ 2021-06-16 20:23 UTC (permalink / raw)
To: 9fans
Quoth ori@eigenstate.org:
> Our compilers will sometimes produce a warning about
> a non-interruptible temporary:
> ...
> Why do we warn about non-interruptible
> temporaries? What issues am I missing?
Silence to this question means no one knows, right?
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* Re: [9fans] non-interruptible temporary: why do we care?
2021-06-16 20:23 ` unobe
@ 2021-06-16 20:28 ` ori
2021-06-17 19:32 ` Charles Forsyth
2021-06-16 21:10 ` Anthony Martin
2021-06-20 14:53 ` [9fans] help Spock via 9fans
2 siblings, 1 reply; 10+ messages in thread
From: ori @ 2021-06-16 20:28 UTC (permalink / raw)
To: 9fans
Quoth unobe@cpan.org:
> Quoth ori@eigenstate.org:
> > Our compilers will sometimes produce a warning about
> > a non-interruptible temporary:
> > ...
> > Why do we warn about non-interruptible
> > temporaries? What issues am I missing?
>
> Silence to this question means no one knows, right?
>
I pinged Charles off list and got a response -- it means
we're falling into the rathole; in other words, we're
accessing a global variable.
The right thing to do (IMO) is make the compiler allocate
on the stack, and then the warning would be unneded.
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* Re: [9fans] non-interruptible temporary: why do we care?
2021-06-16 20:23 ` unobe
2021-06-16 20:28 ` ori
@ 2021-06-16 21:10 ` Anthony Martin
2021-06-16 21:28 ` unobe
2021-06-20 14:53 ` [9fans] help Spock via 9fans
2 siblings, 1 reply; 10+ messages in thread
From: Anthony Martin @ 2021-06-16 21:10 UTC (permalink / raw)
To: 9fans
unobe@cpan.org once said:
> Quoth ori@eigenstate.org:
> > Why do we warn about non-interruptible
> > temporaries? What issues am I missing?
>
> Silence to this question means no one knows, right?
There is nothing new under the sun.
Date: Mon, 4 Apr 2005 14:10:20 -0400
From: Russ Cox <russcox@gmail.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
Subject: Re: [9fans] 'non-interruptable temporary' warning
Message-ID: <ee9e417a0504041110596cc301@mail.gmail.com>
the compiler is warning you against its own laziness.
in this case it is using a global temporary to hold the
intermediate value of (lba = f->lba) while converting
it to uchar. if you had another thread running through
this code it would use the same temporary.
[...]
Cheers,
Anthony
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* Re: [9fans] non-interruptible temporary: why do we care?
2021-06-16 21:10 ` Anthony Martin
@ 2021-06-16 21:28 ` unobe
0 siblings, 0 replies; 10+ messages in thread
From: unobe @ 2021-06-16 21:28 UTC (permalink / raw)
To: 9fans
Quoth Anthony Martin <ality@pbrane.org>:
> There is nothing new under the sun.
>
> Date: Mon, 4 Apr 2005 14:10:20 -0400
> From: Russ Cox <russcox@gmail.com>
> To: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
> Subject: Re: [9fans] 'non-interruptable temporary' warning
> Message-ID: <ee9e417a0504041110596cc301@mail.gmail.com>
>
> the compiler is warning you against its own laziness.
> in this case it is using a global temporary to hold the
> intermediate value of (lba = f->lba) while converting
> it to uchar. if you had another thread running through
> this code it would use the same temporary.
>
> [...]
>
> Cheers,
> Anthony
Thanks for the quotation, Anthony. I had used
9fans.topicbox.com/groups/9fans to search 'non-interruptible', not
'non-interruptable': I should have searched the actual error.
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* Re: [9fans] non-interruptible temporary: why do we care?
2021-06-16 20:28 ` ori
@ 2021-06-17 19:32 ` Charles Forsyth
0 siblings, 0 replies; 10+ messages in thread
From: Charles Forsyth @ 2021-06-17 19:32 UTC (permalink / raw)
To: 9fans
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yes, I'm not sure why it doesn't do that, but probably if I try to add that
code I'll soon find out!
On Wed, Jun 16, 2021 at 9:29 PM <ori@eigenstate.org> wrote:
> Quoth unobe@cpan.org:
> > Quoth ori@eigenstate.org:
> > > Our compilers will sometimes produce a warning about
> > > a non-interruptible temporary:
> > > ...
> > > Why do we warn about non-interruptible
> > > temporaries? What issues am I missing?
> >
> > Silence to this question means no one knows, right?
> >
>
> I pinged Charles off list and got a response -- it means
> we're falling into the rathole; in other words, we're
> accessing a global variable.
>
> The right thing to do (IMO) is make the compiler allocate
> on the stack, and then the warning would be unneded.
>
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* [9fans] help
2021-06-16 20:23 ` unobe
2021-06-16 20:28 ` ori
2021-06-16 21:10 ` Anthony Martin
@ 2021-06-20 14:53 ` Spock via 9fans
2021-06-20 15:32 ` Marshall Conover
2 siblings, 1 reply; 10+ messages in thread
From: Spock via 9fans @ 2021-06-20 14:53 UTC (permalink / raw)
To: 9fans
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* Re: [9fans] help
2021-06-20 14:53 ` [9fans] help Spock via 9fans
@ 2021-06-20 15:32 ` Marshall Conover
2021-06-20 18:46 ` U Cirello
2021-06-20 21:14 ` Ethan Gardener
0 siblings, 2 replies; 10+ messages in thread
From: Marshall Conover @ 2021-06-20 15:32 UTC (permalink / raw)
To: 9fans
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The most recent humpback whale sighting I could find is this:
https://www.stuff.co.nz/environment/125480446/humpback-whales-put-on-spectacular-show-in-sounds
Live long and prosper,
Marshall
On Sun, Jun 20, 2021 at 10:55 AM Spock via 9fans <9fans@9fans.net> wrote:
--
Have a good day,
Marshall Conover
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* Re: [9fans] help
2021-06-20 15:32 ` Marshall Conover
@ 2021-06-20 18:46 ` U Cirello
2021-06-20 21:14 ` Ethan Gardener
1 sibling, 0 replies; 10+ messages in thread
From: U Cirello @ 2021-06-20 18:46 UTC (permalink / raw)
To: 9fans
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that's why I don't unsub 9fans
On Sun, Jun 20, 2021 at 8:33 AM Marshall Conover <marzhall.o@gmail.com>
wrote:
> The most recent humpback whale sighting I could find is this:
> https://www.stuff.co.nz/environment/125480446/humpback-whales-put-on-spectacular-show-in-sounds
>
> Live long and prosper,
>
> Marshall
>
> On Sun, Jun 20, 2021 at 10:55 AM Spock via 9fans <9fans@9fans.net> wrote:
>
>
>
> --
> Have a good day,
>
> Marshall Conover
> *9fans <https://9fans.topicbox.com/latest>* / 9fans / see discussions
> <https://9fans.topicbox.com/groups/9fans> + participants
> <https://9fans.topicbox.com/groups/9fans/members> + delivery options
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>
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* Re: [9fans] help
2021-06-20 15:32 ` Marshall Conover
2021-06-20 18:46 ` U Cirello
@ 2021-06-20 21:14 ` Ethan Gardener
1 sibling, 0 replies; 10+ messages in thread
From: Ethan Gardener @ 2021-06-20 21:14 UTC (permalink / raw)
To: 9fans
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But where are the nuklear wessels?
On Sun, Jun 20, 2021, at 4:32 PM, Marshall Conover wrote:
> The most recent humpback whale sighting I could find is this: https://www.stuff.co.nz/environment/125480446/humpback-whales-put-on-spectacular-show-in-sounds
>
> Live long and prosper,
>
> Marshall
>
> On Sun, Jun 20, 2021 at 10:55 AM Spock via 9fans <9fans@9fans.net> wrote:
>
>
> --
> Have a good day,
>
> Marshall Conover
> *9fans <https://9fans.topicbox.com/latest>* / 9fans / see discussions <https://9fans.topicbox.com/groups/9fans> + participants <https://9fans.topicbox.com/groups/9fans/members> + delivery options <https://9fans.topicbox.com/groups/9fans/subscription> Permalink <https://9fans.topicbox.com/groups/9fans/T1bf00692daa5f082-M97f0a8e6e9023e7290decde7>
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2021-01-04 3:32 [9fans] non-interruptible temporary: why do we care? ori
2021-06-16 20:23 ` unobe
2021-06-16 20:28 ` ori
2021-06-17 19:32 ` Charles Forsyth
2021-06-16 21:10 ` Anthony Martin
2021-06-16 21:28 ` unobe
2021-06-20 14:53 ` [9fans] help Spock via 9fans
2021-06-20 15:32 ` Marshall Conover
2021-06-20 18:46 ` U Cirello
2021-06-20 21:14 ` Ethan Gardener
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