Newsgroups: comp.parallel.pvm
From: sjalali@nortel.ca
Subject: Re: pvm_spawn args
Organization: Deja News - The Leader in Internet Discussion
Date: Wed, 11 Mar 1998 21:27:53 -0600
Message-ID: <6e7kl3$j36$1@nnrp1.dejanews.com>

Hello,
   Thanks, the malloc() solution works, but I really meant to post the
   version where memory allocation is done via "array" declaration,
   which still produces the SIGSEGV:

   char task_arg[3][MAX_RNAME];    // Allocates memory !
   strcpy( task_arg[0], "-p ");
   strcpy( task_arg[1],  "\0" );   // or  " "  as second arg
   strcpy( task_arg[2],  "\0" );   // or  " "  as second arg

....

  if( pvm_parent() == PvmNoParent ){
    cout << "task_arg is: " ;
    for( numt=0; numt < 3; numt++ )
        cout << task_arg[numt] << "#";
    cout << "\n Done. " << endl;

    /* start up slave tasks */
    numt = pvm_spawn( "sjtask",
              (char **)  task_arg,  PvmTaskDefault, "", nproc, tids);
        // If  this ^^^ I don't cast then compiler says:
        //    passing `char (*)[20]' as argument 2

    cout << "NUMT = " << numt << endl;
  }
....


When I run it, I get:

floyd:~/pvm3/YY> sjhj X.IN Y.IN
Args are: X.IN
Args are: Y.IN
task_arg is: -p###
 Done.
Segmentation fault

I  wonder why the two memory allocations work so differently?

Susheel


In article <3506489C.167E@aei-potsdam.mpg.de>,
  Tom Goodale <g00dale@aei-potsdam.mpg.de> wrote:
>
> You aren't allocating the memory properly in the second example:
>
> sjalali@nortel.ca wrote:
> >
> > Hello,
> >
> > Could somebody tell me why:-
> >
> > Following "args" to a spawned task work well:
> >
> >    char *task_arg[] = { "-ivhg0 ", " -pPA", (char *)0 };
>
> The compilor allocates memory at compile time for the strings, as it
> knows thir lengths.
>
> >    numt = pvm_spawn( "sjtask", (char **)  task_arg,
> >                               PvmTaskDefault, "", nproc, tids);
> >
> > While the following variation does not (causes SIGSEGV):
> >
> >    char *task_arg[3], tmp_str[MAX_RNAME];
>
> You are just defining an array of length three holding pointers to
> character strings here.  The memory for the strings has not yet been
> allocated.
>
> >    ostrstream t_arg1( tmp_str, MAX_RNAME);
> >    strcpy( task_arg[0], "-ivhg0 ");
>
> Writing to unallocated memory -> seg-fault.
>
> You need to do task_arg[0] = (char *)malloc(8*sizeof(char)) first.
>
> >    t_arg1 <<  " -p" << mytid << ends;
> >    strcat( task_arg[1], t_arg1.str() );
> >    task_arg[2][0] = '\0';
> >
> > Basically, this a test case for what I want -
> > to be able to pass into args a variable
> > value character string, so I can spawn a task,
> > then have it join a group, then calculate the TID of another
> > task and pas that TID as a command line arg to another
> > task being spawned here.
> >
> > Thanks,
> >  Susheel
> > --
> > Susheel Jalali,
> > sjalali@nortel.ca
> >
> > DISCLAIMER:  My views are mine; may or may NOT be shared by my employer
> >
> > -----== Posted via Deja News, The Leader in Internet Discussion ==-----
> > http://www.dejanews.com/   Now offering spam-free web-based newsreading
>
> I hope this helps.
>
> Tom
>


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