Question

I am working on an app which will allow me to login to a remote telnet server and monitor statistics. The problem is that the telnet server has a minimum refresh rate of 10 seconds, and the refresh rate varies slightly depending on server load (the report itself has this refresh rate, not the server). I need the front-end of this system to refresh more often than every 10 seconds (5 seconds minimum). I have somewhat been able to accomplish this by forking, but eventually the timings synchronize (it’s a gradual process which I am assuming is due to remote server loads).

Child Code:(i have removed quite a bit of code relating to how the app logs in and accesses the report, but it is basically key-presses through 7 menus to get to the page which refreshes – I can include if needed):

// 1 - Telnet Handshaking and initial screen load
$sHandshaking = '<IAC><WILL><OPT_BINARY><IAC><DO><OPT_BINARY><IAC><WILL><OPT_TSPEED><IAC><SB><OPT_TSPEED><IS>38400,38400<IAC><SE>';
// 2-4 - Keypresses to get to report (login, menus, etc. - Removed)

// Loop and cache
while(1){
    //  4 - View Report
    $oVT100->listen(); 
    $reference = $temp;
    $screen = $oVT100->getScreenFull();
    if(empty($screen)){
        Failed:
        echo "FAILED";
        file_put_contents($outFile,array('html'=>"<div class=\"header\"><font color='red'>Why are things always breaking?!<font color='red'></div>"));
        goto restartIt; // If screen does not contain valid report, assume logout and start at top
    }else{
        $screen = parseReport($oVT100->getScreenFull());
        $temp = json_decode($screen);
        // Check old report file, if different save, else sleep a bit
        $currentFile = file_get_contents($outFile);
        if($screen !== $currentFile){
            file_put_contents($outFile,$screen);
            sleep(5);
        }else{
            sleep(1);
            //usleep(500000);
        }
    }
}

As you can see with the child’s code above, it logs in then infinite loops the report. It then writes the screen out to a cache file (if it is different from the existing file). As a dirty workaround to the refresh issue, I wrote a parent to fork:

$pids = array();

for($i = 0; $i < 2; $i++) {
    sleep(5);
  $pids[$i] = pcntl_fork();

  if(!$pids[$i]) {
    require_once(dirname(__FILE__).'/checkQueue.php');
    exit();
  }

}

for($i = 0; $i < 2; $i++) {
  pcntl_waitpid($pids[$i], $status, WUNTRACED);
}

I immediately noticed the timing offset and had to spawn three children instead of two to keep under 5 seconds; but the timing worked for a few days. Eventually, all the children were updating the file at the same time and I had to restart the parent. What would be the best solution to monitor the child processes so that I maintain a refresh interval of less than five seconds?

[EDIT]
This is not a running log, it is a file which contains current call statistics for a call center. The data in the cache file needs to be no less than 5 seconds old at any time, but eventually all of the children sync and write to the log at nearly the same time. The issue isn’t really with the local file, it is inconsistent remote server response times which eventually leads to the child processes running getting their report at the same time.

Answer 1

I’m hoping there’s a better solution, but here’s how I solved it – I feel kind of stupid for not having thought of this in the beginning:

$currentFile = file_get_contents($outFile);
if($screen !== $currentFile){
    if(time()-filemtime($outFile) > 2){
        file_put_contents($outFile,$screen);
        sleep(5);
    }else{
        echo "Failed, sleeping\r";
        sleep(2);
    }
}else{
    sleep(1);
    //usleep(500000);
}

basically, I check the file write time of the cache file and if it is less than 2 seconds ago, sleep and re-execute loop. I was somewhat hoping there would be a solution contained within the parent app but I guess this works…