🚀 go-pugleaf

> In article <255@husc6.HARVARD.EDU> (mitsuharu hadeishi) writes:
> Please correct me when I am wrong, but I'm under the impression that the
> Amiga has both time-sliced multi-tasking and, a routine called Wait() hat
> lowers the priority of an application.  The application is supposed to
> call Wait() when it has nothing to do.

As I understand it, Wait() doesn't really change the task's priority, 
it simply relinquishes that processes's time slice.  So I tell my program
to Wait(), the 68000 goes out and does a round of the other tasks, which
might include lower priority tasks.  It gets back to me, checks the thing 
it waiting on, still waiting, and we go around again.

> How do Amiga programmers handle continuous mouse tracking so their programs 
> can change the cursor shape as the cursor enters different kinds of 
> objects?

This is normally handled by Intuition, which is in itself a process.  It
keeps track of all the mouse movements, and will switch the mouse pointer
image for you if you change windows.  A task can ask to be informed of all
mouse movement, just a few specific mouse events (like clicking on certain
gadgets, menu selections,  or the case of that task's window becoming the 
selected window, etc.), or no mouse events at all.  So really, the 
programmer has most of this done automatically, and since intuition and the
input devices run as separate tasks, they can use the CPU time more 
efficiently and they don't get bogged down very easily.

> My Menu Clock runs as a SystemTask style task, drawing the time in the
> menu bar only when the application has asserted, by calling SystemTask,
> that it is okay to style a couple of cycles to do the drawing. 

MY Menu Clock runs as a normal program (I usually send it off as a slightly
lower priority process so if I get busy it won't slow me down).  Its 
essentially a loop that reads the system clock, displays the time, and then 
usually Wait()s for a minute before looping.  Every so often, when its awake, 
it will make sure its visible by pushing itself up as top window and maybe 
displaying the date or something.

> Some things you can't do on a Mac:
> 1.) Time-slice Multitask two vanilla application programs. (Andy Hertzfeld
> said that he decided not to do it in Servant because the amount of task
> state you need to swap in the current applications makes the swap to
> slow.)  (You can multi-task applications and desk accessories though. And
> there have been some pretty powerful desk accessories released: Click-On
> WorkSheet, MockWrite and MiniWrite, and Acta (an outline editor) spring to
> mind.)

There's no such thing as a "Desk Accessory" on an Amiga, everything's a 
process or a task.  A process is a task with a bit more information that's
needed to use the DOS; all tasks must talk to device drivers directly (no
trouble, just a lower level of access than via DOS).  All programs started
from WorkBench or CLI are processess; thay may in turn start up tasks.

> 2.) give tasks of the same class priorities.  Withing the constraints of
> memory, you can have "w" applications active at once, "x" desk accessories,
> "y" vbl tim-slice tasks, and "z" device drivers.
> Are there any Amiga programmers who needed task priorities?  If so, why ?

Priorities are useful mainly to set the importance of programs.  I don't
want my clock program to slow down a compilation or big calculation, so I
give it a lower priority and it won't get any time if the time's not
available.  So it just hangs back and, as soon as the time is available, 
it gets updated.  The Amiga custom chips help alot with multitasking, since
whenever a task does a synchronous blitter, disk, sound, etc. operation, 
it will Wait(), the custom chip will do the operation via DMA, and the 68000 
will have some free time for other tasks.

> I'm not trying to flame, I'm trying to learn.

I'm always learning, and trying to supply some intelligent answers here.

> --- David Phillip Oster		-- "We live in a Global Village."
> Arpa: oster@lapis.berkeley.edu  --
> Uucp: ucbvax!ucblapis!oster     -- "You are Number Six."
-- 
============================================================================
Dave Haynie    {caip,ihnp4,allegra,seismo}!cbmvax!daveh

	These opinions are my own, though if you try them out, and decide
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