Subject:
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Re: NQC 2.0 and some math questions
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Newsgroups:
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lugnet.robotics.rcx.nqc
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Date:
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Fri, 1 Oct 1999 06:05:14 GMT
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Viewed:
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2447 times
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On semaphores...
There was a lot of discussion a long time ago on whether NQC should use
semaphores to protect temp variables between tasks.
There isn't an atomic test-and-set bytecode, so the only way I know of
implementing sempaphore would be to use bitflags and assign one bit per
task.
In the end, I decided that semaphore implementation was just too slow and
cumbersome on the RCX, and probably unwarranted most of the time during
expression evaluation. My solution was to just duck the problem entirely
and make sure that temp variables are never shared between tasks. This
has the odd consequence that if a subroutine (not a function) is called
from two different tasks, it cannot allocate local variables or temp
variables.
Dave
In article <37F3DC70.58E60D04@get2net.dk>, Jacob Schultz
<dungeonmaster@get2net.dk> wrote:
> Dave Baum wrote:
> > My personal feeling on this, however, is that if you're running around
> > changing y amd z in one task while calculating with them in another,
> > you're just asking for trouble.
> I think that if you do something like this you should use a semaphore
> to secure no tasks access y and z simultanously. But that wastes another
> variable storing the sema.
--
reply to: dbaum at enteract dot com
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Message has 1 Reply:
 | | Re: NQC 2.0 and some math questions
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| (...) There is a way to do it even if you have no test and set, though I can't remember it off the top of my head, and it is slow. Don't see how using bitflags helps? Cheers, Ben. -- (URL) grandfather once told me that there are two kinds of people: (...) (25 years ago, 1-Oct-99, to lugnet.robotics.rcx.nqc)
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