workers misbehaves

[xalgord]

When I set workers to somewhat like high numbers, it gets locked to (Scanning 0/total_urls) and doesn't start scanning. Sometimes it happens even if I set workers to 30 while without workers it works fine.

[xalgord]

I think this is due to race conditions, while multiple threads trying to acquire the same lock

[xalgord]

I've rewritten the app.py script code using threading.Semaphore() instead of threading.lock() with some other minor changes in the script and its working fine. You can use as many threads as you want (but don't use more than 100). Making a PR now.