Runtime.exec() and fork() and Process

Question

So let me see if I understand this correctly, and if I don't please fill me in. If I call the following piece of codeRuntime.getRuntime().exec("chgrp rcsweb " + path+fs+orgName);
Runtime.getRuntime().exec("chmod 660 " + path+fs+orgName);where path is the real path to a file, fs is short for File.spearator and orgName is the name of a file, then in the Unix environment, it will fork off a process.
First, I seem to remember one forum topic that mentioned not forgetting about killing the process returned by exec, so I guess I need to add that to my code.
Second, since I am forking off this process inside of a J2EE container, am I actually forming off the entire container, or just the Servlet where Runtime is called, or what?
Third, how can I prevent the error java.io.IOException: Not enough space
at java.lang.UNIXProcess.forkAndExec(Native Method)
at java.lang.UNIXProcess.<init>(UNIXProcess.java:54)
at java.lang.Runtime.execInternal(Native Method)
at java.lang.Runtime.exec(Runtime.java:546)
at java.lang.Runtime.exec(Runtime.java:413)
at java.lang.Runtime.exec(Runtime.java:356)
at java.lang.Runtime.exec(Runtime.java:320)when I do not have the option of changing my VM size? Is killing the Process (and using waitFor()) going to take care of this issue?
I appreciate your help.

Answer 1

OK, after writing a few test programs, it is indeed clear..on unix (at least on solaris) when calling runtime.exec(..) The ENTIRE VM does indeed get forked. Therefore if your current Memory allocation for you VM is sitting at say 64MB (or you initial memory setting), another 64MB process will be created, even if you doing something as a simple
exec("ls");
I also tried putting runtime.exec call in its own thread hoping that if it was not in the main thread, that only that process would be forked..to no avail..the entire vm is indeed forked everytime...making runtime.exec damn near useless for server side work, and very dangerious..as you can essentialy assume you always need 2x your memory requirements.
If anyone has figured out a workaround...any suggestions greatly appreciated.
Some thoughts on some work-arounds
1. Run 2 VMs (then when native calls are required..send a message to the 'native-calling vm' (insure its memory footprint is very low)
2. Write your exec method via JNI (or does JNI calls also result in a fork of the vm on unix..)
Test code below (threaded version)
import java.util.*;
import java.io.*;
public class test5 extends Thread
     public void run()
          int loops = 0;
          while (true)
               loops++;
               System.out.println("---- iteration " loops "---");
               makeNativeCall();
     public static void main(String[] args)
          try
               System.out.println("testing on OS: " + System.getProperty("os.name"));
               // Allocate a nice chunk of memory
               byte[] bytes = new byte[1024 * 1000 * 50];
               test5 tst = new test5();
               tst.start();
               while (true)
                    Thread.sleep(1000);
     catch(Exception e)
     {e.printStackTrace();}
public void makeNativeCall()
          Runtime runtime = Runtime.getRuntime();
InputStream stderr = null;
InputStream stdout = null;
          OutputStream stdin = null;
Process proc = null;
long totalMem = (long)(runtime.totalMemory()/1024);
long freeMem = (long)(runtime.freeMemory()/1024);
long usedMem = (long)((totalMem - freeMem));
System.out.println("VM REPORT: TOTAL(" totalMem") FREE("+freeMem+") USED(" usedMem")" );
try
proc = runtime.exec("sleep 1");
stderr = proc.getInputStream();
stdout = proc.getErrorStream();
stdin = proc.getOutputStream();
String line = null;
int i = 0;
String error = "";
int exitVal = proc.waitFor();
if (exitVal != 0)
System.out.println("ERROR " +exitVal);
System.out.println("DETIAL" +error);
catch(Exception e)
e.printStackTrace();
finally
if (stderr != null)
try{stderr.close();}catch(Exception ignore){ignore.printStackTrace();}
               if (stdout != null)
try{stdout.close();}catch(Exception ignore){ignore.printStackTrace();}
               if (stdin != null)
try{stdin.close();}catch(Exception ignore){ignore.printStackTrace();}
if (proc != null)
try{proc.destroy();}catch(Exception ignore){ignore.printStackTrace();}