How to stop delay when streaming data from a script as URL to an Applet?

Question

I have a strange problem and do not know what is causing it. Hope someone here with some experience can help.
I have a Java Applet which makes a line graph of data. The data source is to be streaming, where the first chunk of data comes from what is already in a data file, and then new data is sent whenever it is ready. The problem in brief is that if I just collect and show the data from the data file and do not stream everything works fine. If I also have the streaming and wait for a long time, everything works fine, but when the applet is first loaded, the graph is not shown until after a long delay time.
Here is a snippet of the applet code:
         String dataendpoint = "http://phpfunction.php";
         URL url = new URL(dataendpoint);
         InputStream is = url.openStream();
         String line;
         InputStreamReader isr = new InputStreamReader(is);
         BufferedReader br = new BufferedReader(isr);
         while ((line = br.readLine()) != null) {
               // my code here to handle each line of data which prepares it for
               // showing on a line graph.
         } In the above, I show the dataendpoint variable hardcoded, but in reality this comes as an Applet parameter. It is a URL of a php script which is on the same server as the applet's code and there are no access problems here.
The PHP script does the following: It first opens a data file, parses it and prints it out to its standard output using echo or printf statements. The script then enters a loop where it periodically looks to see if new data has been made available. If so, that new data is also printed out to the standard output.
The PHP script looks like this (in pseudo code):
   // open data files, read lines, and send to standard output using echo
   // flush buffers using ob_flush() and flush() calls
   while (1) {
      sleep(30);
      // get new data, if any, then send to standard output
      // flush buffers again
   Again my problem: If I have the PHP script exit before the while loop everything works fine, my applet makes the graph immediately.
However, if I include the while loop, then initially the applet does not appear, not until some time afterwards, and then the applet works like it should, scrolling along every time new data arrives.
I have done a Wireshark sniff and I can see that the initial data is being sent out the the browser and applet immediately. So I do not think it is a buffering problem on the PHP side.
I have wrapped every Applet code line with debug print statements and from the Java console I see that the Java Applet is stopping at this line:
InputStream is = url.openStream();
Can someone explain what is happening here? Why the delay in returning from the openStream() function and how to avoid it?
By the way, the server is Linux and the Applet is being run on Windows Vista, and I have tried both Internet Explorer and Firefox, both give the same behavior.
Thanks in advance!
Steve, Denmark

Answer 1

I still cannot solve this problem, but I have some more observations:
1) yes it is a JApplet, and yes, the data streaming is performed in a separate thread.
2) Wireshark sniffing shows that data sent out by the PHP datasource on the server is sent immediately, and is not buffered (am using ob_start(), ob_flush() and flush() alls in the PHP script).
3) On Windows Vista, using Internet Explorer or Firefox, there is a constant 30 second delay before the Applet returns from this line: InputStream is = url.openStream();
4) After this 30 seconds, data appears in the Applet, but it can be seen also with java console debug prints that the data seems to be buffered. The newest data shown in the Applet is not the newest data sent to the client by the PHP datasource script.
5) On a SUSE Linux client, the Applet works as it should, there is no delay time in showing the data.
It appears as if there is on Windows a buffering of data which I do not wish to have and which does not occur on Linux. I need to find out how to get the URL openStream() call to return immediately allowing the initial data to be read and shown on the Applet. And I need to remove the buffering of data so that the data can be shown on the Applet when it arrives.
Can anyone help? Why does this work on Linux but not on Windows, and what can I do, at best within the Java code, to get the Applet to work on Windows as it does on Linux?
Thanks!
Steve, Denmark