Software Multitasking

[t0xic]

Hey everyone!

I have finally ported JamesM's multitasking code to my kernel. I can call fork() and create new tasks, but they all have the same EIP. If I want them each to start a new function, i.e. function1(), function2(), and function3(), do I just set the EIP value in the task structure to the location of the function and then switch to the task?

Thanks,

Michael

[astrocrep]

I to am quiet firmilar w/ his multi-tasking code...

Yes...

If you want to copy the fork code...

call it "start_task" and have it take a void *thread... then just assign the value of thread to the eip.

I don't have the exact syntax cause I am not at my home pc... but thats how ya do it, and it works for me!

Good Luck

-Rich

[t0xic]

Thanks for the quick reply!
I am working on implementing the start_task() now!

Michael

[JamesM]

Fork() returns zero if you are the child process, and nonzero (The PID of the child process) if you are the parent. So, a start_task function could read something like:

Code: Select all

void start_task(void (*func)(void*), void *arg)
{
  if (fork() == 0)
    func(arg);
}

Pretty simple, really.

EDIT: I really should get round to writing the documentation for the multitasking code I just haven't had time so far!

[t0xic]

I was changing the eip in the task structure. so I just need to do a function call? That's easier than I thought!
Thanks for the code anyhow. You documented it wonderfully, and it was very easy to port (just a few debugging errors in my kernel).

Thanks,
Michael

[lukem95]

i havnt seen this documentation/code, can somebody post a link to it?

i'm hoping to implement software multitasking as soon as i get binaries loading correctly (fingers-x'd by sunday night)

[JamesM]

I haven't released it to the public as yet, I was waiting until I'd written the accompanying tutorial. But *sigh* if you want it...

http://www.jamesmolloy.co.uk/downloads/ ... ing.tar.gz

Cheers,

JamesM

[astrocrep]

Fork() returns zero if you are the child process, and nonzero (The PID of the child process) if you are the parent. So, a start_task function could read something like:

Code: Select all

void start_task(void (*func)(void*), void *arg)
{
  if (fork() == 0)
    func(arg);
}

Pretty simple, really.

EDIT: I really should get round to writing the documentation for the multitasking code I just haven't had time so far!

Wow... thats really a good idea... then you could just add the code to remove it from the scheduler right at the bottom... when ever func(arg) returns...

-Rich

[t0xic]

Yep,

Well right now, I'm not using the IRQ0/PIT scheduler. I just want to make sure that it will work. Whenever I call switch_task(), I get a page fault, so i still trying to debug this. I would post my ported code or bochs dump, but I'm not at home right now.

[Edit]: I already had to change some of the init_task() and fork() code because I was getting a page fault accessing the task structure. So I just identity mapped the structure with 0x7. [/Edit]

--Michael

[razor-x]

Fork() returns zero if you are the child process, and nonzero (The PID of the child process) if you are the parent. So, a start_task function could read something like:

Code: Select all

void start_task(void (*func)(void*), void *arg)
{
  if (fork() == 0)
    func(arg);
}

Pretty simple, really.

EDIT: I really should get round to writing the documentation for the multitasking code I just haven't had time so far!

Wow... thats really a good idea... then you could just add the code to remove it from the scheduler right at the bottom... when ever func(arg) returns...

-Rich

I used this method now and it seems to be working If I create 3 seperate tasks, and place a loop in each task everything works ok, but when a task returns or finishes I get a page fault. Is this because the task isn't running anymore (and so, doesn't exisit?) and the scheduler wants switch to that task?

This is my task list:

Code: Select all

PID              ESP                EBP                EIP            PAGE
1                0x00000000         0x00000000         0x00000000     0x008100
2                0xdfffff74         0xdfffff9c         0x001000dc     0x008800
3                0xdfffff74         0xdfffff9c         0x00100106     0x008f00

but I get this page fault;

Code: Select all

Page fault! ( present read-only ) at 0x0x12bd890 - EIP: 0xc00830b

I don't understand this... why do I get page fault at this addres and EIP? It isnt the EIP of the task that just returned.. (If i place a loop at this task, everything is ok.)

How can I see if a task isn't running anymore?

(yes you're right.. I'm still a beginner, but I'm learning! )

btw. Thanks for the great tutorials JamesM, I'm really learning alot from it!

[JamesM]

Hi,

That return address seems to be garbage, and so i reckon your task is finishing, returning, then the start_task function returns, and pops a garbage return address off the stack. Modify your function to look something like

Code: Select all

void start_task(void (*func)(void*), void *arg)
{
  if (fork() == 0)
  {
    func(arg);
    kill_task();
    for(;;);
  }
}

That way you can have a function called kill_task that removes th current task from the ready queue. the for(;;); afterwards is so the task spins at the current location until the scheduler runs, so it doesn't return to a garbage stack.

Have fun!

James

[razor-x]

Why didn't I think of that?

Thanks, I'm going to try it out!

[t0xic]

Razor, thanks for asking that question!

[razor-x]

Razor, thanks for asking that question!

np!

I still haven't got it right... But I'll get there.... I hope

[lukem95]

that looks like some mighty fine code you got there James, very portable, and easy to plug in your own scheduler.

can i ask how (if you've started) far you are into the documentation for it? i spent a good few hours exploring it and gave implementing it a go, however i have one tiny problem that may be either a bug (not likely) or a problem in my code.

anyway, when i set up current_directory and try to switch to it using the function defined in your paging code (and updated to have dir->physicalAddr), the computer just hangs. Does anyone know why this might be?

Again, very nice code though, im enjoying working with it immensly. looking forward to some documentation/companion tutorial.

Lukem