Java SE (Java Platform, Standard Edition)

So the problem can be summarized as follows. I have a call out to the operating system from Java to obtain the value of “vmstat” which returns a value from every “x” seconds based on the refresh rate. To do This I use a command similar to this

Runtime rt = Runtime.getRuntime();
String[] comm = new String[] {"vmstat","1"};
Process proc = rt.exec(comm);

I can then loop around capturing the output and parsing it. Simple.... This approach works on Linux, Mac OS, HP-UX, AIX and Solaris however it fails under Windows. It sits there and simply waits. Now this appears to be a common problem based on the number of postings on it. This article(http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html) suggests a number of approaches to solve the problem. I’ve tried them all and the good news is that they appear to work for a single atomic call that returns all of its output then exits. However commands such as “vmstat/iostat/sar” etc. return output periodically based on their refresh rates and don’t seem to work at all.

There are plenty of hits in google but no one really seems to suggest a solution. Now Im sure this worked in the past and Im almost certain that I haven’t changed the code.

I’ve tried calling

java myexec cmd /c "c:\\cygwin\\bin\\ls.exe"

Which returns the first line of the directory and then exits.

java myexec cmd /c "c:\\cygwin\\bin\\ls.exe"

simply hangs.... whilst

java myexec cmd /c dir

Works fine.... So my believe its the combination of java and cygwin and the way io is redirected. If anyone has a chance to look at it.... I’ll be very grateful. Code for simple testcase below.

import java.util.*;
import java.io.*;


class StreamGobbler extends Thread {

InputStream is;
String type;

StreamGobbler(InputStream is, String type) {
this.is = is;
this.type = type;
}

public void run() {

try {
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line = null;
while (true) {
if (is.available() == 0) {
try {
Thread.sleep(10);
} catch (InterruptedException ie) {
}
continue;
}

line = br.readLine();
if (line == null) {
System.out.println("Error");
} else {
System.out.println(line);
}

}
} catch (IOException ioe) {
ioe.printStackTrace();
}

}

}
public class myexec {

public static void main(String[] args) {

try {
String osName = System.getProperty("os.name");
System.out.println(osName);

Runtime rt = Runtime.getRuntime();
Process proc = rt.exec(args);

// any error message?
StreamGobbler errorGobbler = new StreamGobbler(proc.getErrorStream(), "ERROR");

// any output?
StreamGobbler outputGobbler = new StreamGobbler(proc.getInputStream(), "OUTPUT");

// kick them off
errorGobbler.start();
outputGobbler.start();

// any error???
int exitVal = proc.waitFor();
System.out.println("ExitValue: " + exitVal);
} catch (Throwable t) {
t.printStackTrace();
}
}
}

Edited by: dgiles on Apr 3, 2009 6:27 AM