Subj : Re: segmentation fault while using setjmp
To   : comp.os.linux.development.system,comp.os.linux,comp.os.linux.questions
From : Larry I Smith
Date : Tue Jun 29 2004 06:18 am

naveen wrote:
> Hello *,
> 
> Here I'm trying to switch control between three threads in a cycle -
> parent, child1, child2 in that order.
> But after the first cycle of execution i get a segmentation fault. I
> guess the problem is with the stack allocated for each thread. I tried
> increasing the stack size and i still get the segmentation fault, but
> this time after completing a few more cycles.
> Can anybody explain this:
> 
> #include <stdio.h>
> #include <setjmp.h>
> #include <unistd.h>
> #include <signal.h>
> 
> sigjmp_buf  context[3];
> int     crt = 0;
> 
> void parent()
> {
>       while(1)
>         fprintf(stderr, "Parent process\n");
> }
> 
> void child(int *i)
> {
>       while(1)
>         fprintf(stderr, "Child process %d\n", *i);
> }
> 
> /* create child context and return to parent */
> void create(int i)
> {
>       if (sigsetjmp(context[i], 1)) {
>         child(&crt);
>       } else {
>         char stack[1024];
>         siglongjmp(context[0], -1);
>       }
> }
> 
> /* context switch */
> void run_thread()
> {
>       int next = (crt + 1) % 3;
> 
>       if (!sigsetjmp(context[crt], 1)) {
>         crt = next;
>         siglongjmp(context[crt], -1);
>       }
> }
> 
> void handler(int sig)
> {
>       signal(SIGALRM, handler);
>       alarm(1);
> 
>       run_thread();
> }
> 
> main()
> {
>       signal(SIGALRM, handler);
>       alarm(1);
> 
>       if (!sigsetjmp(context[0], 1)) {
>         create(1);
>       }
>       if (!sigsetjmp(context[0], 1)) {
>         create(2);
>       }
>       parent();
> }

Use the glibc posix threads library.
The setjmp function family is not intended
for thread creation and context switching.

Regards,
Larry

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