Long polling locking up other AJAX calls

Question

I'm looking to do long polling to "push" some data down to the client and I'm also making other unrelated AJAX calls to the server in parallel with the long polling. It appears that my other AJAX calls won't complete until the long poll has received a response (either from a response or timeout). When I step through the Javascript, it appears that the 2nd AJAX request is being sent at the proper time, but the response isn't being received until the long poll request gets a response. Any idea what is going on?

Here is the code for the long polling portion:

Server side:

    function getPlaylistTracksIfChanged($playlist_id, $numClientTracks) {
  $reportChange = false;
  for($i = 0; $i < 10; $i++) {
   $numServerTracks = $this->PlaylistTrack->find('count', array(
     'conditions' => array('playlist_id' => $playlist_id)
    )
   );

   if($numClientTracks != $numServerTracks) {
    $reportChange = true;
    break;

   }

   sleep(3);

  }

  if($reportChange) {
   $playlist_tracks = $this->PlaylistTrack->find('all', array(
    'conditions' => array('playlist_id' => $playlist_id),
    'order' => array('PlaylistTrack.position') 
    )
   );

   $this->set('playlist_tracks', $playlist_tracks);
   $this->layout = false;
   $this->render('show_playlist_tracks_list');

  } else {
   $this->autoRender = false;
   return 'false';
  }

 }

Client side:

function checkForChangesOnServer() {
 $.post('/getResultsIfChanged/' + playlist_id + '/' + $('#sortable_tracks').children().size(), function(results) {

  if(results == 'false') {
   //alert('no change');
  } else {
   //alert('change');
  }

  checkForPlaylistChangesOnServer();

 });
}

And a sample of another AJAX call:

Server side:

    function getLibraryTracksStartingWithLetter($user_id, $letter) {
  $results = $this->Track->find(
   'all',
   array(
    'conditions' => array(
     'user_id' => $user_id,
     'OR' => array(
      'Track.artist LIKE' => $letter . '%',
      'Track.name LIKE' => $letter . '%'
     )
    ),
    'order' => array('case when Track.artist = "" then 1 else 0 end', 'Track.artist', 'Track.name')
   )
  );

  $this->set('results', $results);
  $this->layout = false;
  $this->render('show_library_results_list');
 }

Client side:

    function loadLibraryResultsForLetter(letter) {
 highlightLetterFilter(letter);

 $.post('/getLibraryTracksStartingWithLetter/' + user_id + '/' + letter, function(results) {
  updateLibraryResults(results);
 });
}

Answer 1

Seems like you experienced the session file lock.

Perform session_write_close() (or corresponding function in cakephp) to close the session in the begin of the ajax endpoint.