Non-blocking Python

1. Non-Blocking Python
By Tao Zhu

2. Tao
Near 10 years exp as
“full-stack”
!
Lead Developer, Perform
Group Plc

3. Repeated Stories
PM: Why slow?
System Admin: Seems
only slow during peak
hour?
Developer: Seems
only slow for login?
DevOps: It is slow in
the login process as
there are many
concurrent write ops
into db and db starts
lock row.

4. “DevOps” is killing
Developers?
Rise of “full-stack”?
How to think like a
“full-stack”?

5. Developing beyond big O
Developer: I have
implemented a binary-
tree algo that is O(log
n)
System Admin: I have
implemented B+ tree
index that is better
than O(log n)
DevOps:
1. The single table is
just too big. Time to
break down into
smaller tables?
2. Is your web server
blocking

6. Blocking? What is that?
A blocking web-server is similar to a
phone call.
!
You need to wait on-line to get a response
and continue

7. A blocking server
Django Server Process
Django Server Process
Django Server Process
Django Server Process
DB
Django Server Process
= context switching (via kernel)
O(logn)

8. Non-blocking server
Tornado Server Process DB
= epoll (via kernel)
O(1)
Event loop

9. How to write Non-block
server?
Call Backs
Coroutine (Decorator)
Yield (Lazy Eval)
def wait_for_messages(self, callback, cursor=None):
if cursor:
new_count = 0
for msg in reversed(self.cache):
if msg["id"] == cursor:
break
new_count += 1
if new_count:
callback(self.cache[-new_count:])
return
self.waiters.add(callback)
!
def cancel_wait(self, callback):
self.waiters.remove(callback)
!
class MessageNewHandler(BaseHandler):
@tornado.web.authenticated
@gen.coroutine
def post(self):
message = {
"id": str(uuid.uuid4()),
"from": self.current_user["first_name"],
"body": self.get_argument("body"),
}
!
cursor = collection.find({'$or': [{'teamA': self.get_argument("body")},{'teamB'
new_message = [self.get_argument("body"),"Matches:"]
withMatch = False
while (yield cursor.fetch_next):
document = cursor.next_object()
withMatch = True
try:
matchDatetime = document.get('data').get('prematch').get('match').get('
except:
try:
matchDatetime = document.get('data').get('match').get('start_time')
except:
pass
!
print matchDatetime
msg_str = matchDatetime+':'+document.get('teamA','')+' v '+ document.get('t
if isinstance(document.get('goalA'), int ):
msg_str = msg_str+' '+str(document.get('goalA',''))+' : '+ str(document
new_message.append(msg_str)
!

10. Non-blocking DB Driver
Non-blocking through out the “Full Stack”
PyMongo? No, it is blocking
Use Motor

11. Demo - World Cup Genie

12. Take-aways
How to think like a “Full-stack”?
Look beyond coding and big(O)
Blocking vs Non-Blocking
Tornado Programming Essentials
Callbacks,Coroutines, Yield
Non-blocking Full Stack - Motor

13. Contact
Blog: Tzu’s {Code of Geeks}
http://geektzu.wordpress.com/author/geektzu/
Email: software-engineer@outlook.com
Github: https://github.com/geektzu/worldcupgenie