Clarify that Reportlab is not thread-safe in pdf section
|Patch needs improvement:
In the doc section on 'Outputting PDFs with Django' there is a strong bias towards Reportlab and Reportlab is great - but it is not thread-safe. This should at least be mentioned and clarified that if if the intention is to offer pdf download from views that can be concurrently accessed - then Reportlab is not the right tool.
I have used Reportlab and now as the usage of my site grows I started to get really strange bugs in reportlab that has taken me now a week to figure out that this is due to threading issues in Reportlab. Had I known this from the start I should not have invested all the effort in using Reportlab, now I need to figure out how to replace it.