[slime-devel] Re: Use of with-lock inside without-interrupts

[Nikodemus Siivola]

On Wed, Aug 6, 2008 at 5:30 PM, Helmut Eller <heller at common-lisp.net> wrote:
> * Nikodemus Siivola [2008-08-06 13:35+0200] writes:

>> and GET-LOCK has the wait wrapped in WITH-INTERRUPTS.
>
> You meant GET-MUTEX, right?

Yes, (and it should be RELEASE-MUTEX in the code).

>> WITH-INTERRUPTS enabled interrupts only if there is an active
>> ALLOW-WITH-INTERRUPTS lexically nested inside each WITHOUT-INTERRUPTS
>> currently on stack. (This is what I was trying to explain while
>> slightly too drunk to make a great deal of sense.)
>
> Would the following also work?
>
>  (without-interrupts (allow-with-interrupts (with-mutex (lock) ...)
>
> Assuming that WITH-MUTEX expands to the ordinary GET-MUTEX/RELEASE-MUTEX pair.

Yes.

WITH-MUTEX is essentially the code below, except that FROB-QUEUE bit
is wrapped in WITH-LOCAL-INTERRUPTS (which is essentially
ALLOW-WITH-INTERRUPTS+WITH-INTERRUPTS).

>>  (let (got-it)
>>    (without-interrupts
>>      (unwind-protect
>>          (when (setf got-it (allow-with-interrupts (get-mutex lock)))
>>             ...frob-queue...)
>>        (when got-it
>>          (release-lock lock)))))

If this was performance sensitive code you'd want to write avoid the
extra WITHOUT-INTERRUPTS, though.

Cheers,

 -- Nikodemus