Mail Archives: opendos/1997/03/13/12:04:44
On Tue, 11 Mar 1997 Colin W. Glenn replied:
> > > Does it allow for controlling applications which do not give up
> > > their time slice on their own?
> > Yes, it's preemptive multitasking! That's one of the major
> > advantages compared to Windows 3.xx/95.
>
> Does this mean you can shoot and kill a task without crashing the
> rest of the system?
Yes, the OpenDOS multitasking kernel can do that - at least in theory,
since each domain runs in a virtual DOS machine, and on closing
tasks, the kernel will try to free remaining resources used by that
task. In practice, it can't do that under all circumstances, because
it needs to detect, that resources were actually allocated by *that*
domain and freeing them does not interfer with other system tasks,
especially in global memory areas. There are scenarios, were this
cannot be determined, and other tasks could have be affected. Of
course, local and instanced data will be lost, including open files,
which have not been flushed before the shutdown. However, all that
has nothing to do with pre-emptive or cooperative multitasking, but
with virtualization.
In short words, the problem with cooperative multitasking is, that
if an application fails, it may hang the whole system, if it does not
give back the token, and the scheduler will wait forever to get it
back. In an pre-emptive system, the scheduler always has the ability,
to get the token back and suspend the task.
Bye,
Matthias
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