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What Is Async, How Does It Work, And When Should I Use It?
- 1. What Is Async, HowDoes It Work, A. Jesse Jiryu Davis @jessejiryudavis MongoDB When Should I Use It? &
- 2. Food in NYC •Subs • Pizza • Omakase
- 3.
- 4. CPU-bound web app ClientServerClients • Throughput bound by computation • No async
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- 6. Normal web app ClientServer • Throughput bound by memory • Async Backend Database, OAuth service, etc. Clients
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- 8. Websocket application Client Server sockets Events sockets Clients •Number of clients bound by memory • Async
- 9. What’s async for? Minimizesresources per connection.
- 10.
- 11. Why is asynchard to code? BackendClient Server request response store state request response time
- 12. Why is asynchard to code? BackendClient Server websocket event store state register for events event time
- 13. Ways to storestate: Coding difficulty Threads Callbacks Memoryperconnection
- 14. Ways to storestate: • Threads • Callbacks ! ... and: ! • Coroutines • Greenlets ! and so on....
- 15. So, what isasync? • Single-threaded • I/O concurrency • Non-blocking sockets • epoll / kqueue • Event loop
- 16. asyncio • AKA “Tulip” •Python 3.4 standard library • Implements PEP 3156 • Standard event loop • Coroutines
- 17.
- 18. Layers 18 Application Protocol Transport Event Loop Selectors asyncio { autobahnwebsockets example.py
- 19. from autobahn import(WebSocketServerProtocol,! WebSocketServerFactory)! example.py
- 20. clients = set()! ! classChatProtocol(WebSocketServerProtocol):! def onConnect(self):! clients.add(self)! ! def onMessage(self, msg):! for c in clients:! if c is not self:! c.sendMessage(msg)! ! def onClose(self):! clients.remove(self)! example.py How is this called?
- 21. Let’s look atthis example.py factory = WebSocketServerFactory(! "ws://localhost:8888")! ! factory.protocol = ChatProtocol! ! loop = asyncio.get_event_loop()! asyncio.Task(! loop.create_server(factory, '127.0.0.1', 8888))! ! loop.run_forever()!
- 22. class BaseEventLoop(events.AbstractEventLoop):! def create_server(! self,protocol_factory, host, port):! ! sock = socket.socket(...)! sock.bind(...)! sock.listen()! sock.setblocking(False)! ! fd = sock.fileno()! self._selector.register(! fd,! selectors.EVENT_READ,! (self._accept_connection, None))! Magic Let’s look at this asyncio reader, writer
- 23. asyncio class BaseEventLoop(events.AbstractEventLoop):! def _accept_connection(! self,protocol_factory, sock):! conn, addr = sock.accept()! conn.setblocking(False)! ! protocol = protocol_factory()! _SelectorSocketTransport(! self, conn, protocol)! class _SelectorSocketTransport(_SelectorTransport):! def __init__(self, loop, sock, protocol):! super().__init__(loop, sock, protocol)! self._protocol.connection_made(self)! ChatProtocol This was our goal
- 24. asyncio class BaseEventLoop(events.AbstractEventLoop):! def _accept_connection(! self,protocol_factory, sock):! conn, addr = sock.accept()! conn.setblocking(False)! ! protocol = protocol_factory()! _SelectorSocketTransport(! self, conn, protocol)! But how exactly is this called?
- 25. Let’s look atthis example.py factory = WebSocketServerFactory(! "ws://localhost:8888")! ! factory.protocol = ChatProtocol! ! loop = asyncio.get_event_loop()! asyncio.Task(! loop.create_server(factory, '127.0.0.1', 8888))! ! loop.run_forever()!
- 26. asyncio magic class BaseEventLoop(events.AbstractEventLoop):! def run_forever(self):! whileTrue:! event_list = self._selector.select()! ! for fd, mask, data in event_list:! reader, writer = data! ! if reader and mask & EVENT_READ:! self._ready.append(reader)! ! if writer and mask & EVENT_WRITE:! self._ready.append(writer)! ! ntodo = len(self._ready)! for i in range(ntodo):! callback = self._ready.popleft()! callback()! accept_connection
- 27. Application asyncio’s eventloop start_server() register(fd,! accept_connection) accept_connection() run_forever() onConnect()
- 28. Review • asyncio usesnon-blocking sockets. ! • Event loop tracks sockets, and the callbacks waiting for them. ! • selectors: wait for network events. ! • Event loop runs callbacks.
- 29. Should I UseIt? Yes: • Slow backend • Websockets • Many connections 29 No: • CPU-bound • No async driver • No async expertise 🍕
- 30. A. Jesse JiryuDavis @jessejiryudavis MongoDB