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Re: [I'm learning C]: Learning to use ucontext

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On 1/29/2012 11:06, Andrey Popp wrote:
> Hello, I started to experimenting with ucontext to implement basic cooperative multithreading and stuccoed with this piece of code:
>

As far as I know, 'ucontext.h' isn't standard C.  I think that's worth 
noting.

> #include<stdlib.h>
> #include<stdio.h>
> #include<ucontext.h>
>
> static ucontext_t routine_main;
> static ucontext_t routine1;
> static ucontext_t routine2;
>
> void runner(int n) {
>    fprintf(stderr, "runner %d\n", n);
>    while(1) {
>      fprintf(stderr, "runner %d\n", n);
>      if (n == 1)
>        swapcontext(&routine1,&routine2);
>      else
>        swapcontext(&routine2,&routine1);
>    }
> }
>
> int main(int argc, char **argv) {
>    char st1c[8192];
>    char st2c[8192];
>
>    if (getcontext(&routine1) == -1)
>      abort();
>    routine1.uc_link =&routine_main;
>    routine1.uc_stack.ss_sp = st1c;
>    routine1.uc_stack.ss_size = sizeof st1c;
>    makecontext(&routine1, (void(*)(void))runner, 1, 1);
>
>    if (getcontext(&routine2) == -1)
>      abort();
>    routine2.uc_link =&routine_main;
>    routine2.uc_stack.ss_sp = st2c;
>    routine2.uc_stack.ss_size = sizeof st2c;
>    makecontext(&routine1, (void(*)(void))runner, 1, 2);
>

Does the line immediately above include a typo?  Did you mean to modify 
the 'routine1' context or the 'routine2' context there?

>    fprintf(stderr, "start executing\n");
>    if (swapcontext(&routine_main,&routine1) == -1)
>      abort();
>    fprintf(stderr, "exiting\n");
>    return 0;
> }
>
> which doesn't work the way it should — it just constantly prints "start executing", which means it doesn't change execution context from routeine_main to routine1 but instead from routine_main to routine_main.

That's unfortunate.

-- 
"The stationery store has moved.  Aaargh!"

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[I'm learning C]: Learning to use ucontext Andrey Popp <8mayday@gmail.com> - 2012-01-29 08:06 -0800
  Re: [I'm learning C]: Learning to use ucontext Shao Miller <sha0.miller@gmail.com> - 2012-01-29 11:42 -0500
  Re: [I'm learning C]: Learning to use ucontext Barry Schwarz <schwarzb@dqel.com> - 2012-01-29 10:07 -0800
  Re: [I'm learning C]: Learning to use ucontext Jens Gustedt <jens.gustedt@loria.fr> - 2012-01-30 20:38 +0100
    Re: [I'm learning C]: Learning to use ucontext Uncle Steve <stevet810@gmail.com> - 2012-01-30 18:58 -0500
      Re: [I'm learning C]: Learning to use ucontext Keith Thompson <kst-u@mib.org> - 2012-01-30 17:05 -0800

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