long polling events

Question

I implement long polling on my web site using php. All work fine, but have one problem. When i open several pages by one user, i have problem with recognize, what event i should to run on that page. If i block event after it work on one page, that event don't work on another. If i don't block, they continue working infinite on every page. If i check event on page that is worked, they still work again after refresh page. I missed right solution, can you help me?

code not very good but working

i just need an idea how to do this

function loadEventAll($uid=0){
    if (isset($_POST['event_log'])){
        $event_log = json_decode($_POST['event_log']); //here event already worked on page
    }
    else $event_log = array();
    for($i=0;$i<25;$i++){            
        $now = time();
        $time = $now;//-$this->triggered_timeout;   

        //sql to cut already worked event
        $noid = array();
        foreach($event_log as $eve){
            if(isset($eve->id)) $noid[] = 'id<>'.$eve->id;
        }
        if (count($noid)) $noid = ' AND ('.implode(' AND ', $noid).') ';
        else $noid = '';   

        //don't try to understand this :)
        $q="SELECT * FROM ig_event WHERE (user_id='$uid' OR user_id=0) AND (((triggered+2>=$time OR triggered=0) AND infinite=0) OR (infinite=1 AND triggered+10<=$time)) AND ($now<time_end or infinite=1) AND time_start<=$time $noid";            
        $link = mysql_query($q); 
        $arr = array();
        if(!$link){ 
            sleep(1);
            continue; // if no event occurring start next iteration
        }
        if (mysql_num_rows($link)){   
            while ($ddd = mysql_fetch_assoc($link)){
                $id = $ddd['id'];
                if ($ddd['direct_call']!=""){ //call js function on page
                    $arr[] = $ddd['direct_call'].':'.$id.':'.$ddd['param'];

                    if ($ddd['success']!=1){
                        if (!$ddd['infinite']) $succ = ' success=1';else $succ='';
                        $ctime = time();
                        $q = "UPDATE ig_event SET $succ,triggered='$ctime' WHERE id='$id'";
                        mysql_query($q);
                    }
                }
                else{ // usually not used
                    if ($this->load->module($ddd['module'])){
                        if (method_exists($this->$ddd['module'], $ddd['action'])){

                            $time = time();                                
                            if (($tarr = $this->$ddd['module']->$ddd['action']($ddd['param'])) and !$ddd['infinite']){                                    
                                $q = "UPDATE ig_event SET success=1 WHERE id='$id'";
                                mysql_query($q);
                            }
                        }
                        else{
                            $q = "UPDATE ig_event SET success=1 WHERE id='$id'";
                            mysql_query($q);
                        }
                        $q = "UPDATE ig_event SET triggered='$time' WHERE id='$id'";
                        mysql_query($q);
                        if (!$ddd['infinite']) $arr[] = 'blank'.':'.$id.':';
                    }    
                }
            }    
            return $arr;
        }  
        sleep(1);
    }  
    return $arr;
}

score 1 · Accepted Answer · answered Sep 11 '12 at 14:42

Here's an idea that we use in a live sysyem. When an event happens, add a timestamp to it. E.g.

id | col1 | col2 | timestamp
------------------------------
 1 | herp | derp | 1347373151
 2 | herp | derp | 1347373152
 3 | herp | derp | 1347373153

Now, when we start long polling we send out the time of the last event we caught or if it's the first request - current time. Then we build the query:

$q = "SELECT * FROM `table` WHERE `timestamp` < ".$lastCaughtEventTime;

If you get any results - return them and exit the php script. The js side should repeat the request as soon as it gets an answer with the highest timestamp from the result set. This way your queries will be minimal and fast. An example code:

function poll() {
    $results = [];
    $start = microtime(true);
    $q = "SELECT * FROM `table` WHERE `timestamp` < " . (int) $_POST['timestamp'];
    while (true) {
        $result = mysql_query($q);
        if (mysql_num_rows($result) > 0) {
            $result = returnResults($result);
            break;
        }
        else {
            if (time() - $start > POLLING_TIMEOUT) {
                die('timeout');
            }
            sleep(2);
        }
    }
    echo json_encode($result);
}

long polling events

1 Answers1