in reply to Re^2: Long Process Waits Until End to Display Results
in thread Long Process Waits Until End to Display Results

OK. merlyn's article deals with how to save the information between invocations to a CGI (using a persistent cache and session key to get the data back). You want to do something different. You want real timeish results. That's different.

You do not need to put the data in the cache; in fact, it is what is storing or buffering the output. You need to set $| to 1 and send the data directly to the user. One big issue, though, is that browsers sometimes "timeout": as noted above if they don't see data in n seconds, they disconnect. I have solved this in the past using timeouts. For now, I'd just write the data directly to the browser with $|=1 and without the cache, and see what happens.

You could use a solution like merlyn's by extending the key to be $session-$line and then retreiving each line individually.

  • Comment on Re^3: Long Process Waits Until End to Display Results

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Re^4: Long Process Waits Until End to Display Results
by C_T (Scribe) on Dec 13, 2004 at 19:14 UTC
    Seems kind of a Catch 22 situation. I need the caching for the reason you allude to. The process which is being buffered can take four hours to complete, so that's why I'm doing the caching and 5-second refreshing, to keep the browser from timing out.

    But it's that caching that's keeping me from seeing real-time results.

    You could use a solution like merlyn's by extending the key to be $session-$line and then retreiving each line individually.

    Can you expand on this idea? I'm not sure how this would work. Wouldn't I lose the ability to display everything that had happend so far and only see the single line that was currently being displayed? Maybe some sample code (if you know any) would be helpful.

    CT

    Charles Thomas
    Madison, WI
[reply]
      I need the caching for the reason you allude to. The process which is being buffered can take four hours to complete, so that's why I'm doing the caching and 5-second refreshing, to keep the browser from timing out.

      I did not get that from your initial post. It might be helpful to see more of your code, particularly the part you use to processess the cache and send the info to the user.

[reply]
        Hopefully this group of code snips will show you what is going on.

        The first part is where I create the fork. The second part is the lengthy process (one of them). The third part is how I display the results so far as processing is ongoing.

        It works fine, except it waits until createCommandFiles() is done before displaying the results instead of displaying the results so far. 

        my $session = getSessionID();
my $cache = getCacheHandle();
$cache->set($session, [0, $buffer]);

#===== Fork off a child process to do the processing
if (my $pid = fork)
{
  delete_all(); # get rid of old parameters
  param('session', $session);
  print redirect(self_url());
}
elsif (defined($pid))
{
  close STDOUT;
  
  open (STDOUT, "-|");    
  
  #===== Make the command files
  $buffer .= "<strong>Creating command files...</strong><br>";
  $cache->set($session, [0, $buffer]);
  createCommandFiles($cache);
  $buffer .= "<strong>Done creating command files.</strong><p>";
  $cache->set($session, [1, $buffer]);

} # if the pid is defined

sub createCommandFiles($)
{
  my $cache = shift or 
    die "Must supply cache to getVersionReports()!\n";

  #===== Change directory to our directory
  chdir($file_dir) or die "Couldn't chdir to $file_dir";
  
  #===== Make each command file
  foreach my $device (@selected_devices_array)
  {
    my $command = "$mkcmdfile -t \"$device\"";
    system($command) and die
      "Could not run command $command : $!";

    $buffer .=  "Created command file for $device.<br>";

    #===== Update the display cache
    $cache->set($session, [0, $buffer]);
  }

} # end of createCommandFiles()

#===================================================================
#    D I S P L A Y  R E S U L T S
#===================================================================
sub displayPushResults($)
{
  my $session = shift or 
    die "Must supply session id to displayPushResults()!\n";
  my $cache = undef;
  my $data = undef;
  
  #===== Get a cache handle
  $cache = getCacheHandle();
  
  #===== Get the session info
  $data = $cache->get($session);
  
  #===== Check validity of session
  die "Could not reconnect to your session!\n" unless ($data and ref $
+data eq 'ARRAY');
  
  #===== Write the header
  print "Content-type: text/html\n\n";
  print "<html>\n";
  print "<head>\n";
  print "<title>CodePusher.cgi</title>\n";
  print "<meta http-equiv=refresh content=5>\n" if (!($data->[0]));
  print "</head>\n";
  print "<body>\n";
  
  AantsHtml::printUWHeader();
  
  #===== Title
  print "<center><h1>Results</h1></center>\n";
  print "<p><p>\n";
  
  #===== Print the results
  print "$data->[1]";
  
  if (!$data->[0])
  {
    print "<p><font color=red>Still processing... please wait!</font><
+br>"; 
  } # if the code push is not done yet
  
} # displayPushResults()

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        CT
        Charles Thomas
        Madison, WI
[reply]
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