Re: [ECOS] problem in thread creation

[Nick Garnett <nickg at ecoscentric dot com>]

Aravind B <arvindb@cranessoftware.com> writes:

> > hi all,
> > i have written small application which has  2 threads.
> > small part of it is as follows:
> > void cyg_user_start(void)
> > {
> >       printf("entering two threads cyg_user_start() function\n");
> >       cyg_thread_create(4,simple_program,(cyg_addrword_t)0,
> >                         "Thread A",(void*) stack[0],4096,
> >                         &simple_threadA,&thread_s[0]);
> >       cyg_thread_create(5,simple_program1,(cyg_addrword_t)1,
> >                        "Thread B",(void*) stack[1],4096,
> >                        &simple_threadB,&thread_s[1]);
> > cyg_thread_resume(simple_threadA);
> > cyg_thread_resume(simple_threadB);
> > }
> > when the control comes for execution of second thread the system
> hangs.
> > on debug i found that the control is in thread.cxx.
> > why is this happening and how to overcome this.
> 
> >Given the terseness of your description, it's hard to tell exactly
> >what the problem is.  First guess is that stack[0] and stack[1]
> >don't contain actual stack pointers.
> 
> >Have you run this code with asserts (kernel debugging) enabled?
> 
> >-- 
> >Gary Thomas <gary@mlbassoc.com>
> ?
> >MLB Associates
> 
> Thanks for ur kind reply
> After debugging i found that problem is in following code fragment in
> file thread.cxx:
> 
> 		Cyg_Thread::add_to_list( void )
> -	127	{
>  	128	    // Add thread to housekeeping list
>  	129	    Cyg_Scheduler::lock();
>  	130	
> -	131	    if( thread_list == 0 )
>  	132	        list_next = this;
>  	133	    else {prev != thread_list
>  	134	        Cyg_Thread *prev = thread_list;
> -	135	        do {
> -	136	            if ( this == prev )
>  	137	                break; // found it already!
> -	138	            prev = prev->list_next;
> -	139	        } while ( prev != thread_list );
> -	140	        if ( this != prev ) {
>  	141	            // insert it in the list:
> -	142	            list_next = thread_list->list_next;
> -	143	            thread_list->list_next = this;
>  	144	        }
>  	145	    }
> 
> the control is in the while loop forever as prev == thread_list ( line
> 139 )ie prev has become NULL.

This code will only fail in the way you suggest if something else has
corrupted the thread structures. I suggest you take another look at
the size and placement of your stacks.

-- 
Nick Garnett                    eCos Kernel Architect
http://www.ecoscentric.com/     The eCos and RedBoot experts


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