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QNX Operating System/Discussion/OSTech/InterruptLock()/List of Posts
Forum Topic - InterruptLock(): (8 Items)
   
Update
Daniel Rodrick
11/22/2007 8:19 AM
post2845
InterruptLock()   
Hi,

I'm not sure if this is the right place to ask, but still would appreciate if somebody could feed my inquisitive mind 
(Without getting into the debate of "Why would you want to do this..." et al) :-)

Can I call InterruptLock() recursively? Something like this:

InterruptLock(lock1);
InterruptLock(lock1);
/* do something */
InterruptUnlock(lock1);
InterruptUnlock(lock1);

Will lthe interrupts be enabled after first or second call to InterruptLock()?

And how about this:
InterruptLock(lock1);
InterruptLock(lock2);
/* do something */
InterruptUnlock(lock2);
InterruptUnlock(lock1);

Dan
Brian Stecher
11/22/2007 8:43 AM
post2846
Re: InterruptLock()   
On Thu, Nov 22, 2007 at 08:19:37AM -0500, Daniel Rodrick wrote:
> Can I call InterruptLock() recursively? Something like this:
> 
> InterruptLock(lock1);
> InterruptLock(lock1);
> /* do something */
> InterruptUnlock(lock1);
> InterruptUnlock(lock1);

Nope, InterruptLock() doesn't count (neither does InterruptDisable()). As 
as matter of fact, you'll permanently hang up on the spin lock of the
second InterruptLock.

> And how about this:
> InterruptLock(lock1);
> InterruptLock(lock2);
> /* do something */
> InterruptUnlock(lock2);
> InterruptUnlock(lock1);

You won't hang on this one, but interrupts will be re-enabled after
the first InterruptUnlock().

-- 
Brian Stecher (bstecher@qnx.com)        QNX Software Systems
phone: +1 (613) 591-0931 (voice)        175 Terence Matthews Cr.
       +1 (613) 591-3579 (fax)          Kanata, Ontario, Canada K2M 1W8
Colin Burgess(deleted)
11/22/2007 9:53 AM
post2852
Re: InterruptLock()   
You can use InterruptStatus() to check to see if interrupts are 
currently disabled.

Brian Stecher wrote:
>
> On Thu, Nov 22, 2007 at 08:19:37AM -0500, Daniel Rodrick wrote:
> > Can I call InterruptLock() recursively? Something like this:
> >
> > InterruptLock(lock1);
> > InterruptLock(lock1);
> > /* do something */
> > InterruptUnlock(lock1);
> > InterruptUnlock(lock1);
>
> Nope, InterruptLock() doesn't count (neither does InterruptDisable()). As
> as matter of fact, you'll permanently hang up on the spin lock of the
> second InterruptLock.
>
> > And how about this:
> > InterruptLock(lock1);
> > InterruptLock(lock2);
> > /* do something */
> > InterruptUnlock(lock2);
> > InterruptUnlock(lock1);
>
> You won't hang on this one, but interrupts will be re-enabled after
> the first InterruptUnlock().
>
> -- 
> Brian Stecher (bstecher@qnx.com)        QNX Software Systems
> phone: +1 (613) 591-0931 (voice)        175 Terence Matthews Cr.
>        +1 (613) 591-3579 (fax)          Kanata, Ontario, Canada K2M 1W8
>
> _______________________________________________
> OSTech
> http://community.qnx.com/sf/go/post2846
>

-- 
cburgess@qnx.com
Brian Stecher
11/22/2007 10:01 AM
post2853
Re: InterruptLock()   
On Thu, Nov 22, 2007 at 09:53:33AM -0500, Colin Burgess wrote:
> You can use InterruptStatus() to check to see if interrupts are 
> currently disabled.

But that won't help in the second case, with two different lock variables.
On an SMP system, you could let multiple people into the critical region
if you try something like:

	InterruptLock(lock1);
	if(InterruptStatus() == 0) {
		InterruptLock(lock2);
	}
	....

-- 
Brian Stecher (bstecher@qnx.com)        QNX Software Systems
phone: +1 (613) 591-0931 (voice)        175 Terence Matthews Cr.
       +1 (613) 591-3579 (fax)          Kanata, Ontario, Canada K2M 1W8
Colin Burgess(deleted)
11/22/2007 10:05 AM
post2854
Re: InterruptLock()   
True, but you could change the second InterruptLock to merely a 
spinlock, couldn't you?

eg

status = InterruptStatus();
if ( status ) {
    InterruptLock(&lock2);
} else {
    SPINLOCK(&lock2);
}

Brian Stecher wrote:
>
> On Thu, Nov 22, 2007 at 09:53:33AM -0500, Colin Burgess wrote:
> > You can use InterruptStatus() to check to see if interrupts are
> > currently disabled.
>
> But that won't help in the second case, with two different lock 
> variables.
> On an SMP system, you could let multiple people into the critical region
> if you try something like:
>
>         InterruptLock(lock1);
>         if(InterruptStatus() == 0) {
>                 InterruptLock(lock2);
>         }
>         ....
>
> -- 
> Brian Stecher (bstecher@qnx.com)        QNX Software Systems
> phone: +1 (613) 591-0931 (voice)        175 Terence Matthews Cr.
>        +1 (613) 591-3579 (fax)          Kanata, Ontario, Canada K2M 1W8
>
> _______________________________________________
> OSTech
> http://community.qnx.com/sf/go/post2853
>

-- 
cburgess@qnx.com
Brian Stecher
11/22/2007 10:49 AM
post2857
Re: InterruptLock()   
On Thu, Nov 22, 2007 at 10:05:36AM -0500, Colin Burgess wrote:
> True, but you could change the second InterruptLock to merely a 
> spinlock, couldn't you?
> 
> eg
> 
> status = InterruptStatus();
> if ( status ) {
>     InterruptLock(&lock2);
> } else {
>     SPINLOCK(&lock2);
> }

Yup, and the InterruptUnlock to a SPINUNLOCK in that case.

-- 
Brian Stecher (bstecher@qnx.com)        QNX Software Systems
phone: +1 (613) 591-0931 (voice)        175 Terence Matthews Cr.
       +1 (613) 591-3579 (fax)          Kanata, Ontario, Canada K2M 1W8
Daniel Rodrick
11/23/2007 12:18 AM
post2882
Re: InterruptLock()   
So what is the correct way (in a driver) to obtain two locks on an SMP machine? I don't find "SPINLOCK" macro / function
 anywhere!

[daniel@localhost qnx632]$ grep -Rn SPINLOCK /opt/qnx632/target/
[daniel@localhost qnx632]$ grep -Rn SPINLOCK /opt/qnx632/host/
Brian Stecher
11/23/2007 8:23 AM
post2888
Re: InterruptLock()   
On Fri, Nov 23, 2007 at 12:18:20AM -0500, Daniel Rodrick wrote:
> So what is the correct way (in a driver) to obtain two locks on an SMP
> machine? I don't find "SPINLOCK" macro / function anywhere!

Left as an exercise for the user :-).

It's just the tail end of the InterruptLock inline - the part after
interrupts have been disabled. Ditto with SPINUNLOCK - it's the part in
InterruptUnlock before enabling interrupts.

-- 
Brian Stecher (bstecher@qnx.com)        QNX Software Systems
phone: +1 (613) 591-0931 (voice)        175 Terence Matthews Cr.
       +1 (613) 591-3579 (fax)          Kanata, Ontario, Canada K2M 1W8

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