[mpich-discuss] Problems with terminal-IO and mpiexec

[Pavan Balaji]

Using stdin in MPI is a terrible idea.  Please don't do that.

There are some improvements in mpich-3.0.1 to stdin management.  See if
that helps.  If it doesn't, we'll look into it, but the priority to
solve this will be really really low.  Don't use stdin.  Bad idea.

 -- Pavan

On 07/31/2012 09:26 AM US Central Time, Dr. Wilfried Jakob (IAI) wrote:
> Hi,
> 
> I would appreciate if someone can help me with the following problem:
> 
> I want to have a communication on the root process (rank=0) in such a
> way that single characters are read from the terminal.
> This is achieved in plain C by using  termios.h and the functions
> tcgetattr() and tcsetattr() as shown in the attached test program. With
> gcc  and  Debian Linux this works fine.
> 
> I translated the program with mpicc without any problems and started it
> directly from the command line: it works well.
> Then I started it with
>     mpiexec -f nodes -n 2  tioTestMPI
> and received the following:
> 
> Waiting for input ...
>   error with cbreak
> Waiting for input ...
>   error with cbreak
> 
> A more detailed analysis shows that the call to "tcgetattr" yields the
> error "Invalid argument". This was obtained by a subsequent call to perror.
> 
> A version including prior calls to
>    MPI_Init(&argc, &argv);
>    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
>    MPI_Comm_size(MPI_COMM_WORLD, &size);
> is given by the second program. It yields the same results:
> Waiting for input ...
>   error with cbreak
> lazy slave
> 
> Thanks in advance
> Wilfried Jakob
> 
> Here is the source code of the test program 1:
> =================================================
> #include <stdio.h>
> #include <stdlib.h>
> #include <termios.h>
> #include <unistd.h>
> 
> static struct termios new_io;
> static struct termios old_io;
> 
> int cbreak(int fd) {
>    /* save old terminal settings */
>    if((tcgetattr(fd, &old_io)) == -1)
>       return -1;
>    new_io = old_io;
>    /* change terminal settings */
>    new_io.c_lflag = new_io.c_lflag & ~(ECHO|ICANON);
>    new_io.c_cc[VMIN] = 1;
>    new_io.c_cc[VTIME]= 0;
> 
>    /* set new settings */
>    if((tcsetattr(fd, TCSAFLUSH, &new_io)) == -1)
>       return -1;
>    return 1;
> }
> 
> 
> int getch(void) {
>    int c;
> 
>    if(cbreak(STDIN_FILENO) == -1) {
>       printf("  error with cbreak \n");
>       exit(EXIT_FAILURE);
>    }
>    c = getchar();
>    /* restore old terminal settings */
>    tcsetattr(STDIN_FILENO, TCSANOW, &old_io);
>    return c;
> }
> 
> 
> int main (int argc, char** argv)
> {
>    int  ii;
> 
>    printf ("Waiting for input ...\n");
>    ii = getch ();
>    printf ("  read: \"%c\" = %d\n", (char)ii, ii);
>   
>    printf ("Waiting for input ...\n");
>    ii = getch ();
>    printf ("  read: \"%c\" = %d\n", (char)ii, ii);
>   
>    printf ("\nfinished!\n");
>    return 0;
> }
> =================================================
> 
> Here is the source code of the test program 2:
> =================================================
> #include <stdio.h>
> #include <stdlib.h>
> #include <termios.h>
> #include <unistd.h>
> 
> #include "mpi.h"
> 
> static struct termios new_io;
> static struct termios old_io;
> 
> 
> int cbreak(int fd) {
>    /* save old terminal settings */
>    if((tcgetattr(fd, &old_io)) == -1)
>       return -1;
>    new_io = old_io;
>    /* change terminal settings */
>    new_io.c_lflag = new_io.c_lflag & ~(ECHO|ICANON);
>    new_io.c_cc[VMIN] = 1;
>    new_io.c_cc[VTIME]= 0;
> 
>    /* set new settings */
>    if((tcsetattr(fd, TCSAFLUSH, &new_io)) == -1)
>       return -1;
>    return 1;
> }
> 
> 
> int getch(void) {
>    int c;
> 
>    if(cbreak(STDIN_FILENO) == -1) {
>       printf("  error with cbreak\n");
>       exit(EXIT_FAILURE);
>    }
>    c = getchar();
>    /* restore old terminal settings */
>    tcsetattr(STDIN_FILENO, TCSANOW, &old_io);
>    return c;
> }
> 
> 
> int main (int argc, char** argv)
> {
>    int  ii, rank, size;
> 
>    MPI_Init(&argc, &argv);
>    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
>    MPI_Comm_size(MPI_COMM_WORLD, &size);
> 
>    if (rank == 0) { /* master */
>       printf ("Waiting for input ...\n");
>       ii = getch ();
>       printf ("  read: \"%c\" = %d\n", (char)ii, ii);
>   
>       printf ("Waiting for input ...\n");
>       ii = getch ();
>       printf ("  read: \"%c\" = %d\n", (char)ii, ii);
>   
>       printf ("\nfinished!\n");
>    } /* master */
>    else
>       printf ("lazy slave\n");
> 
>    MPI_Finalize();
>    return 0;
> }
> =================================================
> 
> 
> 
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-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji