So I have this local script generate.php that loops through some special folder structure of websites on my localhost and executes a phantomJS script using the PHP exec function to generate Thumbnails (1200x800) for these projects (These are just websites/php/html).

The problem is, that its really slow. I have about 18 different images to be generated and it takes from 30sec up to a minute for only those 18 which is not what I want. Is there an option to run those 18 execs concurrently with php or maybe there is a phantomJS script that can handle many images at once. Hope someone has an idea.

foreach(folder level 1)
   foreach(folder level 2)
      exec(phantomjs render image)