Simple threaded job scheduler memory issues

Question

Hi,
I'm working on a very simple job scheduler that triggers some processes to be run (based on a config file) and will spawn a thread to run the command every X number of seconds.
My initial version of the code showed an obvious memory leak, starting at about 20MB usage and increasing after running overnight to about 80MB... I have since stripped down the program to a very minimal bit of code that will basically create 100 job objects and trigger threads on each of them to go way and run a Cygwin sleep.exe for 5 seconds and then return, once for each job every 15 seconds. After running the profiler with this within Netbeans, the VM Memory utilisation graph showed a very similar graph, and exhibited the same memory utilisation as my previous version.
I've tried to tweak the code as much as I can with my level of knowledge, so now I'm hoping someone might be able to help out to see if there are any flaws in my code, or any improvements that I could make in order to resolve my problem?
Below is the code for the 3 classes that I'm using:
Main class:
package javascheduler;
import java.util.ArrayList;
public class Main {
    private ArrayList<Job> allJobs = new ArrayList();
    public static Main instance;
    public static void main(String[] args) {
     if (instance == null) {
         instance = new Main();
     instance.loop();
    public Main() {
     // Create lots of jobs
     for (int i = 0; i < 100; i++) {
         Job j = new Job(i);
         allJobs.add(j);
     System.out.println("Created 100 jobs");
    private boolean loop() {
     // Main loop
     int i = 0;
     int x = 0;
     while (true) {
         x++;
         try {
          Thread.sleep(500);
         } catch (InterruptedException ex) { }
         i++;
         if(i >= 10) {
          Runtime.getRuntime().gc();
          i=0;
         for(Job j : allJobs) {
          long now = System.currentTimeMillis();
          // Jobs run every 15 secs
          if(now >= j.getLastRunTime() + 15000 && !j.isRunning()) {
              j.runJob();
}Job class:
package javascheduler;
public class Job {
    private NativeJob runningJob = null;
    private String command = "c:/cygwin/bin/sleep.exe 5";
    private int jobId;
    private long lastRunTime = -1;
    public Job(int id) {
     jobId = id;
    public void runJob() {
     System.out.println("runJob started" + jobId);
     lastRunTime = System.currentTimeMillis();
     runningJob = null;
     runningJob = new NativeJob(command,jobId);
     runningJob.start();
     System.out.println("runJob returned" + jobId);
    public long getLastRunTime() {
     return lastRunTime;
    public boolean isRunning() {
     if(runningJob == null) {
         return false;
     } else {
         if(runningJob.isRunning()) {
          return true;
         } else {
          runningJob = null;
          return false;
}NativeJob class:
package javascheduler;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
public class NativeJob extends Thread {
    String command;
    int jobId;
    boolean running = false;
    Runtime r = Runtime.getRuntime();
    public NativeJob(String command, int i) {
     super();
     this.command = command;
     this.jobId = i;
    @Override
    public  void run() {
     running = true;
         try {
          System.out.println("Running command " + jobId);
          Process p;
          p = r.exec(command);
          int returnCode = p.waitFor();
          p.getErrorStream().close();
                p.getInputStream().close();
                p.getOutputStream().close();
         } catch (IOException ex) {
          Logger.getLogger(NativeJob.class.getName()).log(Level.SEVERE, null, ex);
         } catch (InterruptedException ex) {
          Logger.getLogger(NativeJob.class.getName()).log(Level.SEVERE, null, ex);
         System.out.println("Finished command " + jobId);
         running = false;
    public boolean isRunning() {
     return running;
}Thanks
Adam

Answer 1

Thanks ejp and sabre.
I've made some changes to the code following your suggestions, and am now trying out jconsole on windows (rather than the Netbeans profiler).. I'll post back after I've had it running a little while.
If you could take a quick look at the updates I've made that's be very much appreciated.
Main class:
package javascheduler;
import java.util.ArrayList;
public class Main {
    private ArrayList<Job> allJobs = new ArrayList();
    public static Main instance;
    public static void main(String[] args) {
     instance = new Main();
     instance.loop();
    public Main() {
     // Create lots of jobs
     for (int i = 0; i < 100; i++) {
         Job j = new Job(i);
         allJobs.add(j);
     System.out.println("Created 100 jobs");
    private boolean loop() {
     // Main loop
     int i = 0;
     int x = 0;
     while (true) {
         x++;
         try {
          Thread.sleep(500);
         } catch (InterruptedException ex) { }
         i++;
         if(i >= 10) {
          Runtime.getRuntime().gc();
          i=0;
         for(Job j : allJobs) {
          long now = System.currentTimeMillis();
          // Jobs run every 15 secs
          if(now >= j.getLastRunTime() + 15000 && !j.isRunning()) {
              new Thread(j).start();
}Job class:
package javascheduler;
import java.io.IOException;
public class Job implements Runnable {
    private String[] command = { "c:/cygwin/bin/sleep.exe","5" };
    private int jobId;
    private long lastRunTime = -1;
    Runtime r = Runtime.getRuntime();
    boolean isRunning = false;
    public Job(int id) {
        jobId = id;
    public void run() {
        System.out.println("runJob started" + jobId);
        isRunning = true;
        lastRunTime = System.currentTimeMillis();
        try {
            Process p = r.exec(command);
            StreamGobbler errorGobbler = new StreamGobbler(p.getErrorStream(), "ERROR");
            StreamGobbler outputGobbler = new StreamGobbler(p.getInputStream(), "OUTPUT");
            errorGobbler.start();
            outputGobbler.start();
            int exitVal = p.waitFor();
        } catch (IOException ex) {
            ex.printStackTrace();
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        System.out.println("runJob returned" + jobId);
        isRunning = false;
    public long getLastRunTime() {
        return lastRunTime;
    public boolean isRunning() {
        return isRunning;
}Edited by: Adamski2000 on Aug 2, 2010 3:12 AM