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Threads and Synchronization

Thread not waking up after sleep

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posted 19 years ago

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Hi
In the following programs AcceptAndSaveTransmittedFile servlet spawns the thread SendResponseThread.
The intention is the thread will be spawned when the servlet is initialized and then the thread will look into Transmission
folder and move files to TransmissionReceived folder at 10sec interval.

But after the first time the thread moves the folders , it goes to sleep and doesn not wake up !!!
Any idea why this is happening. I would hughly appreciate if someone can let me know where am making the mistake.

import java.io.*;
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
 
 
public class AcceptAndSaveTransmittedFile extends HttpServlet {
 
 
static int fileCounter = 0;
        File parentDir;
 
    public void init() throws ServletException
    {
fileCounter = 0;
            parentDir = new File("c:\\Transmission");
            parentDir.mkdir();
 
 
            // Invoke thread
            new SendResponseThread();
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException
    {
 
        handleRequest(request, response);
    }
 
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException
    {
 
        handleRequest(request, response);
    }
 
 
public void handleRequest(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException
{
PrintWriter pw = response.getWriter();
String xml = request.getParameter("xml");
xml = "<test>For Test</test>" + fileCounter;
String fileName = "FileName" + fileCounter + ".xml";
 
            File fileReceived = new File(parentDir,fileName);
            FileOutputStream foup = new FileOutputStream(fileReceived);
 
byte buf[] = xml.getBytes();
for(int i=0;i<buf.length;i++) {
foup.write(buf[i]);
}
fileCounter++;
 
pw.println("<html>");
pw.println("<head>");
pw.println("</head>");
pw.println("<body>");
pw.println("<h3>Saved XML file </h3>");
pw.println("</body>");
pw.println("</html>");
}
}
 
 
 
 
 
**************************************************************************************
 
import java.io.*;
import java.util.Date;
 
public class SendResponseThread implements Runnable
{
    Thread t;
    String dirName;
    File destFolder;
    boolean dirCreated = false;
    SendResponseThread()
    {
        dirName = "c:\\Transmission";
        destFolder = new File("c:\\TransmissionResponded");
 
        dirCreated = destFolder.mkdir();
        if(dirCreated)
        {
            System.out.println( destFolder + " created !");
        }else
        {
            System.out.println( "FATAL : " + destFolder + " did not create !");
        }
        System.out.println("SendResponseThread to start ...");
        t = new Thread(this, "SendResponseThread");
        t.start();
        System.out.println("SendResponseThread to started ...");
    }
 
    public void run()
    {
        System.out.println("SendResponseThread running ...");
        File srcFolderFile = new File(dirName);
        String destFolderName = destFolder.getName();
        File destFolderFile = new File("c:\\" + destFolderName);
 
        if(srcFolderFile.isDirectory())
        {
            File srcFiles[] = srcFolderFile.listFiles();
            boolean append = true;
 
            for(int i=0; i < srcFiles.length; i++)
            {
                System.out.println("f.getName() :" + srcFiles[i].getName());
                // Move file to new directory
                try{
                boolean success = srcFiles[i].renameTo(new File(destFolderFile+"\\"+srcFiles[i].getName()));
                if (!success) {
                    System.out.println("File was not successfully moved !");
                }
                }catch(Exception e){
                    e.printStackTrace();
                }
            }
            try
            {   System.out.println("Sleeping after moving " + srcFiles.length + " files");
                Thread.sleep(10000);
            }catch(InterruptedException ie)
            {
                System.out.println("SendResponseThread interrupted." + ie.getMessage());
            }
        }
    } // end run method
}  // end class

[EJFH Added "CODE" tags for formatting.]
[ January 25, 2005: Message edited by: Ernest Friedman-Hill ]

Ernest Friedman-Hill

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posted 19 years ago

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It looks to me as if after the sleep() call, the run() method will return, which will terminate the Thread. Were you expecting something else to happen?

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Gerome Kawa

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posted 19 years ago

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am expecting the run() method to be called after the duration of the sleep. but it is not happening after the first execution of run()

Ernest Friedman-Hill

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posted 19 years ago

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The run() method of a Runnable is invoked exactly once by the Thread. When it returns, the Thread dies. If you want the run() method to keep going after the sleep() returns, put the whole body of the run() method -- or at least the part that you want to repeat -- in a "while (true)" loop.

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Gerome Kawa

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posted 19 years ago

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what does while(true) mean ... i mean what is 'true' or what needs to be 'true' to keep the run() method running always ?

Thanks

Ernest Friedman-Hill

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posted 19 years ago

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This will run the code over and over again.

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David Harkness

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posted 19 years ago

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Originally posted by Gerome Kawa:
what does while(true) mean ... i mean what is 'true' or what needs to be 'true' to keep the run() method running always ?

In the codethe <statements> will be executed repeatedly as long as <expression> evaluates to the literal boolean value "true". Since the literal boolean value "true" is equals to the literal boolean value "true" (itself), "while ( true )" repeats indefinitely. You can use "break" to exit the loop (same with for loops).

If you want something more explicit, how about this?"! done" of course evaluates to "true" since "! false == true".
[ January 27, 2005: Message edited by: David Harkness ]

Guy Allard

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posted 19 years ago

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Even with the while loop, there are other more serious threading issues with that code .....

There are potentially many threads in the Servlet's GET/POST logic.

There is only one SendResponseThread.

Think about .... well, the static file counter for one ....

Guy

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