How to synchronously add files in a queue?
Here are a few suggestions right off the top of my head:
If you just need to keep a log of what files were added, processing status, etc:

since you're doing a lot of I/O you can add another file (ex: named files_queue) and append the filenames one per line. Later you may add additional details (CSV style) about each file (would be a bit of a challenge to search through it if this file grows big).
related to the first idea, if the number of files is not an issue you may create a file (like a .lock file for example) for each file processed and maybe store all processing details in it (and it will be easy to search).  
if your application is connected to a database, create a table (ex: named files_queue) and insert one row per each file. Late you may add additional columns to the table to store additional details about each file. 

If you're looking for queue manager there are a few solutions just a "python queue" google search away. I personally have used RabbitMQ.
Hope this helps,
Cheers!
I have a Django server running which utilizes files in a directory /PROCESSING_DOCS/*.json. An API call dynamically adds more files to this folder. Now I need to maintain a queue which updates the files added into that folder dynamically.
How can I implement this? I don't have any idea.