Randomly generated string seems to be the same if functions are called at very similar times

[eluser]yacman[/eluser]
Where is the code for

Code:

$this->image_file->string_generate();

This model call is not referenced and is what generates your file name (the actual part that is being duplicated).

My guess is your string_generate() is time based, and yes people can make simultaneous requests.

To avoid this, try to isolate users to their own working folders. Instead of uploading to /upload/
use
/upload/[user-id]/ or some unique value that isn't replicated across user sessions.