On the Internet to see a lot of reference and so on, but in practice, I found that most are under different uri handler is not blocked, but for the same handler is blocked (including multiple processes) and not clear code, or environment configuration problem,
Post code (python 3.7 | tornado==6.0.3) :

 
The import tornado. Httpserver 
The import tornado. Ioloop 
The import tornado. Options 
The import tornado. Web 
The import tornado. Gen 
The from datetime import datetime 
The from concurrent. Futures import ThreadPoolExecutor 

The class IndexHandler (tornado. Web. RequestHandler) : 
Def get (self) : 
Print (' index, STR (datetime. Now ())) 
Self. Write (' Index! % s' % STR (datetime. Now ())) 

The class TestHandler (tornado. Web. RequestHandler) : 
Async def get (self) : 
Await tornado. Gen. Sleep (3) 
Print (STR (datetime. Now ())) 
The self. The write (STR (datetime. Now ())) 


Def server_main () : 
Print (' Tornado, Tornado. Version, 'server start! ') 
Application=tornado. Web application (

(r/index, IndexHandler), 
(r/test ", "TestHandler), 
], 
The debug=True, 
) 
Application. The executor=ThreadPoolExecutor (10) 
Http_server=tornado. Httpserver. Httpserver (application, max_header_size=104857600) 
Http_server. Listen (9999) 
Http_server. Start (1) 
Tornado. Ioloop. Ioloop. Current (). The start () 


If __name__=="__main__ ': 
Server_main () 

(note: under Linux, more CPU processes (http_server. Start (2)), is still blocked)

Congestion: