🚀 go-pugleaf

On 12 Sep 1995 17:04:03 GMT Eric Williams @ PCB x5577 (ewill@hpewill.sje.mentorg.com) wrote:
> In article <42qclc$3bu@sashimi.wwa.com>, blackbob@sashimi.wwa.com (G) writes:
> |> 
> |> dollars.  Preemptive multitasking is no more expensive to  imple-
> |> ment  than  cooperative.  It might be cheaper, especially from an
> |> application developer's perspective.

> PMT is (slightly) more expensive, because those systems that
> use it must also implement and require a method of
> synchronization between processes; CMT has built-in
> synchronization.  The Amiga Exec, for example, which had PMT
> from the beginning, had to implement signals and messages
> (and in v1.2, semaphores) in order to keep its processes
> from tripping over each other.  The programmer is required to
> learn this complexity (though actually it's pretty simple;
> Amiga Exec is very clean).

Amiga signals and messages are just means of interprocess communication.
Only semaphores are specifically for syncronization. I am a programmer
myself, and I have not had to use semaphores yet, and it does not seem
likely that I will have to do so.
The only case where you (may) need semaphores is if two programmes share
a piece of memory and could at any time write to that memory. That doesn't
happen often. Semaphores are very simple anyway.

> In Windows, one simply has to call a certain routine
> occasionally.  That routine has the luxury of being
> able to switch contexts while the system is semi-
> quiescent (a luxury comparable to the single spin lock
> allegedly placed on Solaris SMP kernels, which makes
> them comparatively slow).

> But PMT's worth it to avoid being frozen in one's tracks
> by a stupid program that endlessly loops, and it does
> simplify the job for the programmer who wants to write a
> compute-intensive application (e.g. a raytracer, a fluid-
> flow modeller, or a logic simulator, all of which do not
> require user input *during* their computation runs).

Another worth of PMT is that the OS divides the CPU time between
applications, instead of having the applictations themselves divide the
CPU time. This means that the user controls the amount of CPU time given
to programmes, instead of relying on the programmers to be polite.

--
Regards,
 _________________________________________________________________________
/                                                                         \
| Rask Ingemann Lambertsen <gc948374@gbar.dtu.dk>, <e9864029@ebar.dtu.dk> |
|            WWW homepage: http://srv2.gbar.dtu.dk:8001/Rask/             |
|  Keyboard error: <Ctrl> and <Alt> are stuck - press <Del> to continue   |
\_________________________________________________________________________/