shell_exec seems to hang other web requests while running convert

Hi All, The following problem: Our client is converting pdfs to images with a web interface. At the moment I'm using convert from imagemagick with shell_exec (i know i could use the imagick module, but this would require quite a bit of recoding and time at the moment, it was originally running on a windows machine and i couldnt get the imagick module working on that). Is there a quick way to give other web requests to the web server a higher priority than this process? It can take quite a while to convert 100 pdf pages to images in high res with convert. At the moment only 3 images at a time are converted with some crazy ajax logic. But still while these 3 images are converted (can take 20-30 seconds) other requests seem to hang until convert is finished. I know, i can put a & at the end of the command line but then they wouldnt know when the process is actually finished. The server is an ubuntu server with the latest release. It's got Apache: Apache/2.2.8 (Ubuntu) mod_mono/2.0 PHP/5.2.4-2ubuntu5.3 with Suhosin-Patch mod_ssl/2.2.8 OpenSSL/0.9.8g Server at 208.79.206.58 Port 80 Please help. This is rather urgent and needs to be working properly preferably before xmas. Anyway, merry xmas to everyone in case i forget to say that later :-). Tim-Hinnerk Heuer http://www.ihostnz.com