Server Sent Events PHP blocking flow

Question

i dont know if its a problem but, im doing a feed from php to javascript using Server Sent events instead of ajax. All work fine except that, sleep on server side, keeps event source blocking webpage flow. I did a pretty simple code to test, and i got the same results.

I will put the code above.

Server sent events hangs the page flow? its not like ajax thats do a async requests?

The main question is: Server sent events hangs code flow, what i mean is, the page waits for EventSource to keep code execution, every time eventSouce opens a connection or receive a message. I can see this clear when i put a sleep on server side code, my page stops for the sleep time, run for 3 seconds, then hangs again. When i do an ajax call, the call is async, so the code keeps running with ajax in background, even if i put a sleep on server side. I hope can you understand now =p

test.php

                    @set_time_limit(0);
                    //send the proper header
                    header('Content-Type: text/event-stream');
                    header('Cache-Control: no-cache');
                    if(function_exists('apache_setenv')){
                        @apache_setenv('no-gzip',1);
                    }
                    @ini_set('zlib.output_compression',0);
                    @ini_set('implicit_flush',1);
                    for($i = 0; $i < ob_get_level(); $i++){
                        ob_end_flush();
                    }
                    ob_implicit_flush(1);

                $startedAt = time();

                do {

              $time = time();
              echo "id: $startedAt " . PHP_EOL;
              echo "data: {\n";
              echo "data: \"msg\": \"$time\", \n";
              echo "data: \"id\": $startedAt\n";
              echo "data: }\n";
              echo PHP_EOL;
                //@ob_flush();
                @ob_end_flush();
                @flush();   
                usleep(0.5*1000000);
                } while(true);

HTML

if(!!window.EventSource) {
     var source = new EventSource('test.php');
     source.addEventListener('open', function(event) {
     console.log('open');
  }, false);
    source.addEventListener('message', function(event) {
    var data = JSON.parse(event.data);  
    console.log(event.data);
  },false);
}

Just for the record, i have found the problem. My problem was with session locking php from running. session_write_close() did the trick; — Daniel Echizen, Aug 08 '14 at 12:26

score 9 · Answer 1 · answered Nov 20 '14 at 20:18

9

As Daniel answered himself, the problem could be with session lock.

session_write_close();

solved my problem too.

answered Nov 20 '14 at 20:18

Lukas Jelinek

2,337
1
19
12

thank you for this, i had this with a php-websocket, but now decided to user sse instead and forgot about this. This fixed locked connections for me! – Sascha Grindau Nov 23 '21 at 09:04
"Session Locks: First and foremost, if you're using sessions for whatever reason you will need to make them read-only on the stream. If they're writable, this will lock them everywhere else, so any page loads will hang while the server waits for them to become writable again. This is easily fixed by calling; session_write_close();" https://stackoverflow.com/a/70219693/1066234 – Avatar Mar 13 '23 at 12:41

Server Sent Events PHP blocking flow

1 Answers1