Hello,

More of my philosophy about stack memory allocations and about
preemptive and non-preemptive timesharing..

I am a white arab from Morocco, and i think i am smart since i have also
invented many scalable algorithms and algorithms..

I think i am smart, and as you are noticing in my below thoughts that
i am abstracting smartly so that to make you understand preemptive and
non-preemptive timesharing , other than that i will also give you
an interesting stack memory allocation algorithm in Delphi and
Freepascal so that to use it smartly with my below sophisticated
Stackful coroutines Library, so i will extend my sophisticated Stackful
coroutines Library so that to support it smartly, and here it is:

--

var pool: array [1..limit] of integer;
memory: array [min..max] of integer;
top: integer;

procedure initialize;

var index: integer;

begin
for index := 1 to limit do
pool[index] := empty;
top := min − 1
end;

procedure allocate( index, length: integer; var address: integer);

begin

address := pool[index];
if address <> empty then
pool[index] := memory[address]
else
begin
address := top + 1;
top := top + length;
if not (top <= max)
then raise Exception.Create('Stack overflow..')

end
end;

procedure release( index, address: integer);
begin
memory[address] := pool[index];
pool[index] := address
end;

--

More of my philosophy about about the paper and about preemptive and
non-preemptive timesharing and more..

I have just forgotten to post about who has written the following
paper about cooperative and preemptive tasking:

https://users.ece.cmu.edu/~koopman/pubs/koopman90_HeavyweightTasking.pdf

Here is the Professor Phil Koopman of Carnegie Mellon University from
Department of Electrical and Computer Engineering who has written
this paper:

https://users.ece.cmu.edu/~koopman/personal.html

And note that i am calling, in my thoughts below, cooperative and
preemptive tasking: "preemptive and non-preemptive timesharing"

More of my philosophy about Intel 8051 controller and about preemptive
and non-preemptive timesharing and more..

I have just quickly read the following interesting paper and it says
that judicious use of cooperative tasking techniques can also often meet
an embedded system's multitasking requirements, while giving better
performance and a simpler software environment than a preemptive
multitasker, so read it carefully here:

https://users.ece.cmu.edu/~koopman/pubs/koopman90_HeavyweightTasking.pdf

And notice that it also says in the above paper that so that to meet
the requirements with cooperative multitasking you have to move the
time-critical code to interrupt-service routines. And let us look
for example at the Intel 8051 controller here:

https://www.electronicwings.com/8051/introduction-to-8051-controller

So as you notice that it has many hardware interrupts that you can
use so that to make the cooperative tasking efficient, and i think it
also comes with two clock timers interrupts that you can use to
implement preemptive multitasking if you want, and you have also to know
about interrupt latency when programming embedded systems with hardware
controllers, and you have to know that the hardware interrupts have to
get serviced fast enough and often enough, so you shouldn't disable
interrupts for too long a period of time, and just to give you an idea
, look for example at the nonbuffered communication UART (Universal
Asynchronous Receiver Transmitter) operating at 38,400 bits per second
will interrupt every 208 microseconds. This is 1/38,400*8 because they
will interrupt for every byte (8 bits), and a processor or controller
running at 25MHz executes most of its instructions in
2 or 3 system-clock periods. That would be an average of 120 nanoseconds
(1/25,000,000*3). In theory, this means you could execute as
many as 1,730 instructions in the interrupt interval. So that was only
in theory, now you have to do the reality check. You must take into
consideration that there are more interrupts than just that
communication channel. The timer interrupt will be firing off every so
often. And the communication interrupt itself will have interrupts
disabled for good period of time, and not only that, but there is also
the tasks switch that can be expensive, so you have to think about
it efficiently.

So i invite you to read my below thoughts about preemptive and
non-preemptive timesharing and more so that to understand much more
efficiently:

More of my philosophy about preemptive and non-preemptive timesharing
and more..

I have just took a smart look at Modula-2 language(Modula-2 is a
structured, procedural programming language developed between 1977 and
1985 by Niklaus Wirth at ETH Zurich, and he has also developed Pascal
language, read about Niklaus Wirth here:
https://en.wikipedia.org/wiki/Niklaus_Wirth), and i think Modula-2
language was among the first languages that has provided preemptive and
non-preemptive timesharing with coroutines, but the preemptive
timesharing in Modula-2 uses Interrupt handling using IOTRANSFER, but it
is best reserved for programs that will run without operating system
support. Installing an interrupt handler on a multiuser system is not
feasi­ble because doing so would affect other users. (For this reason,
IOTRANSFER is not a mandatory feature of Modula-2.) Even on single-user
systems, IOTRANSFER can be difficult to use because installing an
interrupt handler causes the old interrupt handler (which most likely
belongs to the operating system) to be lost. So this is why i think that
the best way in modern operating systems is to use non-preemptive
timesharing with coroutines, so this is why i am providing you with my
sophisticated implementation of stackful coroutines, read about it in my
thoughts below:

More of my philosophy about timesharing that is a Solution to Computer
Bottlenecks..

I invite you to look at the following very interesting video about
timesharing that is a Solution to Computer Bottlenecks:

https://www.youtube.com/watch?v=Q07PhW5sCEk

I think i am smart, and you have to understand one important thing
and it is: What is the difference between a software architect and
a software engineer?, i think there is an important difference and it
is also like abstracted in the following question:

"How it is made?"

So i think that software engineering works at a higher level than
a software architect, this is why you will notice that i am
quickly implementing a sophisticated stackful coroutines
Library and i am quickly implementing setjmp() and longjmp() with
x64 assembler or code machine, read my below thoughts about them, but
you have to know that my sophisticated stackful coroutines Library
does a kind of timesharing as in the above video, but i think that
there is two kinds of timesharing: the preemptive one, and the
non-preemptive one, but the difference is that the preemptive one does
interrupt with a timer the coroutines from an external scheduler in
a form of function, but notice below that i am implementing the
non-preemptive timesharing in my sophisticated coroutines Library, but
you have to be smart and notice that my way of doing is like the
software architect way, since i am implementing it from the lowest level
with x64 assembler routines that are part of the non-preemptive
scheduler, but not only that, but you have also to look at how i am also
implementing a
sophisticated and much more rich interface in my stackful coroutines
Library, so it is like both software achitecting and software
engineering, so here is all my below thoughts that shows how i am
implementing it quickly, so read it carefully since you have also to
know what's the problem with the stack frames when architecturing and
using the setjmp() and longjmp() so that to implement coroutines:

More of my philosophy and precision about the link of the article and more..

And notice that the link below of the article that shows the problem
of implementing coroutines with just setjmp() and longjmp()
is from the last semester of the second year of the course
called "CS4411 Operating Systems" from Michigan Technological
University, but i think i am smart and those courses are easy
for me, so i invite you to read about this course that requires
both the course of "CS3331 Concurrent Computing" and "CS3421 Computer
Organization", and here it is:

http://www.csl.mtu.edu/cs4411.ck/www/Home.html

More of my philosophy about coroutines and about setjmp() and longjmp()..

I think i am smart, and i will say that with setjmp() and longjmp()
you can implement a generator or the like, but you can not implement
coroutines with just setjmp() and longjmp(), and so that to understand
it, i invite you to read the following article that shows how when you
yield from a first function with a longjmp() to the main body of a
program and when you call another functions with longjmp(), it can make
the stack frames not work correctly, and when you understand it you will
not use setjmp() and longjmp() alone so that to implement coroutines, so
read the following article so that to understand the problem with
the stack frames, and i am understanding it easily: