Re: waiting on a condition

[Peter W. Morreale]

Have you looked at the wait_event() family yet?       Adapting that 
methodolgy might
suit your needs.

I don't know much about preemption yet, however I suspect it would be a 
bug to allow
preemption while the spinlock was held.  In other words, you might need 
to do something like

disable preemption
spinlock
rc = condition
spin_unlock
enable preemption
if (rc)
...

In other words, perform the test on the condition outside of the 
critical region protected by the spin lock.

-PWM


Martijn Sipkema wrote:

> L.S.
>
> I'd like to do something similar as can be done using a POSIX condition
> variable in the kernel, i.e. wait for some condition to become true. The
> pthread_cond_wait() function allows atomically unlocking a mutex and
> waiting on a condition. I think I should do something like:
> (the condition is updated from an interrupt handler)
>
> disable interrupts
> acquire spinlock
> if condition not satisfied
>    add task to wait queue
>    set task to sleep
> release spinlock
> restore interrupts
> schedule
>
> Now, this will only work with preemption disabled within the critical
> section. How would something like this be done whith preemption
> enabled?
>
>
> --ms
>
>
>
>
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--
Peter W. Morreale                            email: morreale@xxxxxxxxxxxxxxx
Director of Engineering                      Niwot, Colorado, USA
Radiant Data Corporation                     voice: (303) 652-0870 x108 
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