title: php flock behaviour when file is locked by one process
body: <p>Let's consider a sample php script which deletes a line by user input:</p>
  
  <pre><code>$DELETE_LINE = $_GET['line'];
  $out = array();
  $data = @file("foo.txt");
  if($data)
  {
      foreach($data as $line)
          if(trim($line) != $DELETE_LINE)
              $out[] = $line;
  }
  $fp = fopen("foo.txt", "w+");
  flock($fp, LOCK_EX);
  foreach($out as $line)
      fwrite($fp, $line);
  flock($fp, LOCK_UN);
  fclose($fp); 
  </code></pre>
  
  <p>I want to know if some user is currently executing this script and file "foo.txt" is locked, in same time or before completion of its execution, if some other user calls this script, then what will happen?
  Will second users process wait for unlocking of file by first users? or line deletion by second users input will fail?</p>