Runtime.exec(), so much fun

Question

I'm at the bang your head on the monitor stage of this.
I have some executables written in C that I need to be able to executed. They require an input file for processing and generate an output file with results, no big deal.
They both run great from a command prompt. (I'm running on linux with j2sdk1.3.0 by the way)
Now if I call one of them with Runtime.exec(), it runs perfectly as expected. Everything goes in, Everything comes out, Everyone is happy.
If I call the other, It says it runs, I get an exit value of 0, the output file is created, but empty.
I thought I could open a shell with Runtime and then try to get it to run from there to see if it would make any difference, but I was unable to get the shell to call the executables to run with the arguments for input. There is something weird with the way Runtime feeds the strings to the shell. I tried a couple variations.
Then I thought, what the hell, I wonder if I can write a shell script that calls the executables and see what I get from there. So I wrote a little script that just calls the executable with one little hard coded input, just to see if it would run. Run the script from a command prompt, works great and as expected. Try to call the simple little script from Runtime.exec() and I get a segmentation fault.
At this point, I'm almost giving up on an easy answer for what in theory should be taking a few lines of code.
If anybody has a clue on how to approach this or what might be causing this, please let me know.
for the whole saga
http://www.javaranch.com/ubb/Forum13/HTML/000198.html
http://www.javaranch.com/ubb/Forum34/HTML/001360.html
Any response here would be appreciated.

Answer 1

I guess clicking on links and reading is too much to
ask.I admit I didn't read the thread there. Shame on me.
But i did this litle test.
Here I have a C program that reads from a file two numbers and writes some lines to another. The names are passed in command line.
#include <stdio.h>
#define NAME "[first test program]"
int main(int argn, char** args) {
  FILE* in = NULL;
  FILE* out = NULL;
  int exitCode = 0;
  int nLoops = 0;
  int nSec = 0;
  int i;
  if(argn < 3) {
    fprintf(stderr, "%s usage: %s inFile outFile\n", NAME, args[0]);
    exitCode = 1;
    goto _exit;
  in=fopen(args[1], "rt");
  if(in == NULL) {
    fprintf(stderr, "%s Cannot open file %s\n", NAME, args[1]);
    exitCode = 2;
    goto _exit;
  out=fopen(args[2], "wt");
  if(out == NULL) {
    exitCode = 2;
    goto _exit;
  fscanf(in, "%d", &nLoops);
  fprintf(stdout, "%s read %d loops from %s\n", NAME, nLoops, args[1]);
  fflush(stdout);
  fscanf(in, "%d", &nSec);
  fprintf(stdout, "%s read %d seconds to sleep from %s\n", NAME, nSec, args[1]);
  fflush(stdout);
  for(i=0; i<nLoops; i++) {
    fprintf(stdout, "%s try to write line %d on %s ... ", NAME, i, args[2]);
    fflush(stdout);
    sleep(nSec);
    fprintf(out, "%s line number %d\n", NAME, i);
    fprintf(stdout, "done\n");
    fflush(stdout);
  fflush(out);
_exit:
  if(in != NULL) fclose(in);
  if(out != NULL) fclose(out);
  return exitCode;
}I created an executable c1 and the I modified the NAME and created another executable c2.
The I wrote a small java test class :
import java.io.*;
public class test {
    public static void main(String[] args) {
     String[] cmd1 = { "./c1", "input1", "out1" };
     String[] cmd2 = { "./c2", "input2", "out2" };
     Runtime r = Runtime.getRuntime();
     try {
         Process p1 = r.exec(cmd1);
         Process p2 = r.exec(cmd2);
         BufferedReader r1 =
          new BufferedReader(new InputStreamReader(p1.getInputStream()));
         BufferedReader r2 =
          new BufferedReader(new InputStreamReader(p2.getInputStream()));
         String l1 = r1.readLine();
         String l2 = r2.readLine();
         while(l1!=null || l2!=null) {
          if(l1 != null) System.out.println("from java proc 1:\t" + l1);
          if(l2 != null) System.out.println("from java proc 2:\t" + l2);
          l1 = r1.readLine();
          l2 = r2.readLine();
     } catch (Exception ex) {
         ex.printStackTrace();
}The imput files contains on a single line the number of lines to write on the output file and a sleep time between lines, like:
100 1This test runs fine on my linux box.
I have a RedHat 7.0 on a PIII, kernel 2.2.16-22 .
You can try and see if it is working on your box. I think it will. My guess is that the problem is somehow on the second c program.
I didn't read the other thread, so maybe the answer is there, but I'll ask: the problem is with a specific program, or allways happen with the second that you run?
Anyway, it will be nice if you can isolate the problem in three small source files and send them here.
Regards,
Iulian