Path: utzoo!attcan!uunet!snorkelwacker!apple!oliveb!amiga!cbmvax!valentin
From: valentin@cbmvax.commodore.com (Valentin Pepelea)
Newsgroups: comp.sys.amiga
Subject: Re: OS 101 (more questions)
Message-ID: <10693@cbmvax.commodore.com>
Date: 7 Apr 90 04:24:02 GMT
References: <15003@snow-white.udel.EDU> <5463@sugar.hackercorp.com> <40@kalahari.cs.utexas.edu> <23894@usc.edu> <620@lovelady.cs.utexas.edu> <603@vela.acs.oakland.edu> <6363@umd5.umd.edu>
Reply-To: valentin@cbmvax (Valentin Pepelea)
Organization: Commodore, West Chester, PA
Lines: 39

In article <6363@umd5.umd.edu> steveg@umd5.umd.edu (Steve Green) writes:
>
> -Can someone tell me how the Amiga scheduler works??  Does each process get
>  even time??  Priorities??

The Amiga executive, the Exec, has a pre-emptive scheduler which allots tasks
of equal priority equal amounts of time on a round robin fashion. Tasks
of higher priority run as long as they need to. Lower priority tasks run only
if no other higher priority tasks are ready to run.

> -Also, if one process is waiting for terminal I/O, is that process taken off
>  the queue for cpu time or is that cpu time wasted??

There are two task queues: the ready-to-run queue and the wait-queue. If a
task want to grab some terminal input, it the input is not already available,
the task is put in the wait-queue and the task in the ready-to-run queue
with the highest priority is scheduled to run.

> -What primitives exist for a process to request more or less cpu time??

None. A task may only raise or lower its priority.

> -Are any of the OS functions a process??  That is, if a process decides to
>  hog the CPU, will the OS crash or get confused?

The term "process" means something else on the Amiga. A "process" is a superset
of a task which is authorized to call AmigaDOS functions. (for disk I/O)
In order to hog the CPU a task must either forbid task switching through the
Forbid() call, or disable interrupts through the Disable() call.

Disabling interrupts can interfere with with device drivers functions such as
serial I/O, but otherwise no harm can be caused to the computer.

Valentin
-- 
The Goddess of democracy? "The tyrants     Name:    Valentin Pepelea
may distroy a statue,  but they cannot     Phone:   (215) 431-9327
kill a god."                               UseNet:  cbmvax!valentin@uunet.uu.net
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