?
Solved

URLConnection blocked

Posted on 2002-06-26
6
Medium Priority
?
682 Views
Last Modified: 2009-12-16
I have two URLConnections opened at the same time in my java applet.  One waits up to 1 minute for a webpage to return, while the other gets a web page and returns almost instantly.  I find that after the applet has made several requests for a web page it deadlocks.  The deadlock appears to be caused by the long waiting URLConnection blocking in the getInputStream function which stops the other quick URL connections from being created.  Does anyone know how a url connection is implemented lower down.  Is a deadlock occuring? Is URLConnection sharing one socket or stream or something?

0
Comment
Question by:msbroadf
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
6 Comments
 
LVL 92

Expert Comment

by:objects
ID: 7112454
are the two connections made in one thread?  If so, then certainly one will block the other.
Can you post the relevant part of your code so we can see whats going on.
0
 
LVL 9

Expert Comment

by:Ovi
ID: 7112767
Put every connection in a separate thread which will not block the main thread, and synchronize them if you need to. Can you post sample code from your applet ?
0
 

Author Comment

by:msbroadf
ID: 7115192
public class Engine extends Thread
{
  private volatile boolean shutdown;
  ...
  ...

  public void run()
  {
    while (!shutdown)
    {
      String line = getTunnelLine()
      if (!shutdown) processLine(line);
    }
     
  /**
   * Opens the connection to the proxy
   */
  private URLConnection openTunnel(String file)
  {
    URLConnection result;
   
    try
    {
      URL url = new URL("http" + (applet.secure ? "s" : "") + "://" + tunnelHost + ":" + (applet.secure ? "443" : new Integer(tunnelPort).toString().trim()) + file);
      result = url.openConnection();
    }
    catch (Exception e)
    {
      System.err.println("openTunnel:" + e);
      result = null;
    }
    return result;
  }

  /**
   * Gets a line of data from the HTTP tunnel
   * This function gets the long HTML page
   * and blocks all other openTunnel request
   * from executing. It is called from the engine
   * run().
   */
  private String getTunnelLine()
  {
    String result = "";
   
    if (getLineBuffer.size() > 0)
    {
      result = (String) getLineBuffer.firstElement();
      getLineBuffer.removeElementAt(0);
    }
    else
    {      
      URLConnection conn = openTunnel("/csd/proxy.cgi?cssesstoken=" + cssesstoken + "&unum=" + uniqueNum++ + "&csconnectionstyle=sendandclose");
      if (conn != null)
      {
        conn.setAllowUserInteraction(true);
        conn.setUseCaches(false);
        conn.setDoInput(true);
        if (connectTunnel(conn))
        {
          applet.message(applet.getResourceString("r50"));
          BufferedReader br = getBufferedReader(conn);
          if (br != null)
          {
            String lines = readBufferedReader(br);
            if (lines != null)
            {
              last_io = new Date();
              result = parseLines(lines);
              if (debugIn) System.err.println("In =" + result);
            }
            else
              error = true;  
            closeBufferedReader(br);
          }
          else
            error = true;
        }
        else
          error = true;
        closeTunnel(conn);
      }
      else
        error = true;
    }
    return result;
  }


  /**
   * The tunnel outline calls the quick
   * html page.
   * Tunnel the data sent to the server
   * so it looks like an HTTP POST request.  This
   * function is called when the user clicks buttons
   * on the applet to send data back to the server
   * however. It cant get bufferedreader after a while
   * because getTunnelLine is also blocking on get
   * buffered reader
   */
  public void tunnelOutline(String data)
  {
    PrintWriter out = null;
    BufferedReader in = null;
    boolean success;

    String postData = "cssesstoken=" + cssesstoken + "&" + "cschatinput=" + encode(data) + "&" + "csconnectionstyle=sendonly\r\n";
    if (useProxy)
    {
      URLConnection conn = openTunnel("/CSJava/CSCPROXY.CGI?cssesstoken=" + cssesstoken + "&cschatinput=" + encode(data) + "&csconnectionstyle=sendonly");
      if (conn != null)
      {
        conn.setUseCaches(false);
        conn.setDoInput(true);
        if (connectTunnel(conn))
          in = getBufferedReader(conn);
        else
          error = true;
        closeTunnel(conn);
      }
      else
        error = true;
    }
    else
    {
      Socket s = getSocket(tunnelHost, tunnelPort);
      if (s != null)
      {
        out = getPrintWriter(s, true);
        in = getBufferedReader(s);
        out.print("POST /CSJava/CSCPROXY.CGI HTTP/1.1\r\n" +
                  "Host: " + tunnelHost + ":" + tunnelPort + "\r\n" +
                  "Content-type: application/x-www-form-urlencoded\r\n" +
                  "Content-length: " + postData.length() + "\r\n\r\n");
        out.print(postData);
        out.flush();
      }
    }
    if (in != null)
    {
      try
      {
        StringBuffer buf = new StringBuffer();
        int input;
        while ((input = in.read()) > -1)
          buf.append((char)input);
        if (!useProxy) out.close();
        in.close();
      }
      catch (Exception e)
      {
        error = true;
      }  
    }
    if (error && debugOut) System.err.println(data + " may not have been sent");
  }

  private BufferedReader getBufferedReader(URLConnection conn)
  {
    BufferedReader result;
   
    try
    {
      result = new BufferedReader(new InputStreamReader(conn.getInputStream()));
    }
    catch (Exception e)
    {
      System.err.println("getBufferedReader error: " + e.getMessage());
      result = null;
    }
    return result;
  }

}
0
Get real performance insights from real users

Key features:
- Total Pages Views and Load times
- Top Pages Viewed and Load Times
- Real Time Site Page Build Performance
- Users’ Browser and Platform Performance
- Geographic User Breakdown
- And more

 
LVL 92

Expert Comment

by:objects
ID: 7115483
Can't see any obvious problem in your code.
Have you checked what your server is recieving and whether it is blocking?
0
 
LVL 16

Accepted Solution

by:
heyhey_ earned 300 total points
ID: 7121140
some browsers limit the numbers of simultaneous URLConnection, if I remember correctly IE allows only 4 simultaneous connections. so if there are 4 connections that for some reason stay opened, fifth one will "block forever".


install naviscope proxy from www.naviscope.com to track the connection number visually.
0
 
LVL 35

Expert Comment

by:girionis
ID: 8893401
No comment has been added lately, so it's time to clean up this TA.

I will leave a recommendation in the Cleanup topic area that this question is:

- points to heyhey_

Please leave any comments here within the
next seven days.

PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER !

girionis
Cleanup Volunteer
0

Featured Post

Optimize your web performance

What's in the eBook?
- Full list of reasons for poor performance
- Ultimate measures to speed things up
- Primary web monitoring types
- KPIs you should be monitoring in order to increase your ROI

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction Java can be integrated with native programs using an interface called JNI(Java Native Interface). Native programs are programs which can directly run on the processor. JNI is simply a naming and calling convention so that the JVM (Java…
Go is an acronym of golang, is a programming language developed Google in 2007. Go is a new language that is mostly in the C family, with significant input from Pascal/Modula/Oberon family. Hence Go arisen as low-level language with fast compilation…
Viewers will learn about basic arrays, how to declare them, and how to use them. Introduction and definition: Declare an array and cover the syntax of declaring them: Initialize every index in the created array: Example/Features of a basic arr…
How to fix incompatible JVM issue while installing Eclipse While installing Eclipse in windows, got one error like above and unable to proceed with the installation. This video describes how to successfully install Eclipse. How to solve incompa…
Suggested Courses
Course of the Month11 days, 11 hours left to enroll

752 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question