wood burning stoves 2.0*
The moose likes Swing / AWT / SWT and the fly likes Main thread is hanging while 2 child threads running?? Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login

Win a copy of Murach's Java Servlets and JSP this week in the Servlets forum!
JavaRanch » Java Forums » Java » Swing / AWT / SWT
Bookmark "Main thread is hanging while 2 child threads running??" Watch "Main thread is hanging while 2 child threads running??" New topic

Main thread is hanging while 2 child threads running??

Praveen Kumar Jayaram
Ranch Hand

Joined: Jul 14, 2008
Posts: 56

I am having a progress bar in my swing application.
Data to update the progress bar comes from an input stream which is got from a process.getInputStream().

I have a Thread which reads in data(from the process.getInputStream()) into a variable . And this variable is accessed by another Thread to update the progress bar seamlessly.

Totally I have 3 threads.
The main thread creates those 2 threads and hangs... It seems the other 2 threads are taking full time to read and update the progress bar.
Even using Thread.yield() is not helping.

I have shared my code sample:

Thread to read the input stream:

public class StreamGobbler implements Runnable
InputStream input = null;
String pid = null;
String solver = null;

StreamGobbler(InputStream in, String pid, String solver)
input = in;
this.pid = pid;
this.solver = solver;
public void run()
InputStreamReader inputReader = new InputStreamReader(input);
BufferedReader br = new BufferedReader(inputReader);
String line=null;

Scanner scan = null;
while ( (line = br.readLine()) != null)
//&& checkPIDOfSolver(pid, solver))
System.out.println(">" + line);
scan = new Scanner(line);
int iter = Integer.parseInt(scan.next());
iteration = String.valueOf(iter).trim();
catch(Exception e)
catch(Exception e)

Thread to update the progress bar continuously:

public class ProgressBarIncrementer implements Runnable {

//run method, this will be called implicitly by start()
public void run() {
File deleteFile = null;
try {
String inputFilePath = delia.getoutputFileName();
int last = inputFilePath.lastIndexOf("\\");
String str = inputFilePath.substring(0, last + 1);

//File deleteFile = new File(str+"solver.res");
if(Delia.getProcessorType() == 'T'){
deleteFile = new File("TIP3DSolver.res");
else if(Delia.getProcessorType() == 'S'){
deleteFile = new File("SPLITVISSolver.res");

int NMAX = Integer.parseInt(getDeliaInstance().getFlowConditionsInstance().NMAX);
while(true) {
int pc = ((Integer.parseInt(iteration)*100)/NMAX);
progressBar.setValue(pc); //Set value
progressBar.setString(String.valueOf(pc) + "%");
progressBar.repaint(); //Refresh graphics
if (deleteFile.exists())
//if file exists stop the thread
} }
catch (Exception err)
deleteFile = null;

Main thread part:

String cmd[] = new String[]{"cmd", "/C","DentonSolver.bat"};
fortranExecutor = Runtime.getRuntime().exec(cmd);

strPid = getPIDOfSolver("tip3dpc202.exe");
if(strPid == null)
DentonLogger.log(Level.SEVERE, "Could not start tip3dpc202.exe");
JOptionPane.showMessageDialog(this.getFrame().getContentPane(), "Could not start tip3dpc202.exe", "Error", JOptionPane.ERROR_MESSAGE);

//create a thread to update progress bar
inc = new Thread(new ProgressBarIncrementer());
//set to maximum priority
//start the thread

//Create another thread for reading the input stream to update the progress bar from solver process
streamGobbler = new Thread(new StreamGobbler(fortranExecutor.getInputStream(), strPid, "tip3dpc202.exe"));


Nathan Pruett

Joined: Oct 18, 2000
Posts: 4121

I'm not sure what would cause the main thread to hang but the ProgressBarIncrementer isn't going to work like that - you're updating the progress bar (a Swing component) from a thread other than the event thread - you're going to need to use SwingUtilities.invokeLater() to update the component on the event thread.

As far as the main thread hanging - I'm not sure if any synchronized methods are being called, or if it's really that the other threads take up all the processor time - have you tried changing the Thread.yield() to Thread.sleep(500) to see if this affects it?

Write once, run anywhere, because there's nowhere to hide! - /. A.C.
wood burning stoves
subject: Main thread is hanging while 2 child threads running??
Similar Threads
Runtime.exec to wait for external application
Thread behave differently and stop on some machines??
input data for external program
problem calling isql or osql from java
who can my question about this code