asyncio: it's all about the cancellation by Bruce Merry

Lightning Talk at PyConZA 2017

1. ASYNCIO: IT’S ALL ABOUT THE CANCELLATION PyConZA 2017 Bruce Merry Bruce Merry asyncio: it’s all about the cancellation PyConZA 2017 1 / 5
2. Simple Server Example async def do_connection(reader, writer): try: while True: line = await reader.readline() if not line: break # Connection was closed writer.write(await process(line)) finally: writer.close() Bruce Merry asyncio: it’s all about the cancellation PyConZA 2017 2 / 5
3. Simple Server Example async def do_connection(reader, writer): try: while True: line = await reader.readline() if not line: break # Connection was closed writer.write(await process(line)) finally: writer.close() loop = asyncio.get_event_loop() task = loop.create_task(do_connection(reader, writer)) ... await task Bruce Merry asyncio: it’s all about the cancellation PyConZA 2017 2 / 5
4. Server Shutdown async def do_connection(reader, writer): try: while True: line = await reader.readline() if not line: break # Connection was closed writer.write(await process(line)) finally: writer.close() Bruce Merry asyncio: it’s all about the cancellation PyConZA 2017 3 / 5
5. Server Shutdown async def do_connection(reader, writer): try: while True: line = await reader.readline() if not line: break # Connection was closed writer.write(await process(line)) finally: writer.close() task.cancel() Bruce Merry asyncio: it’s all about the cancellation PyConZA 2017 3 / 5
6. Server Shutdown async def do_connection(reader, writer): try: while True: line = await reader.readline() if not line: break # Connection was closed writer.write(await process(line)) finally: writer.close() task.cancel() CancelledError Bruce Merry asyncio: it’s all about the cancellation PyConZA 2017 3 / 5
7. Catching Cancellation async def do_connection(reader, writer): try: while True: line = await reader.readline() if not line: break # Connection was closed writer.write(await process(line)) except asyncio.CancelledError: writer.write(b Server shutting down\n ) raise finally: writer.close() Bruce Merry asyncio: it’s all about the cancellation PyConZA 2017 4 / 5
8. Wait With Timeout try await asyncio.wait_for(task, timeout) except TimeoutError: ... Bruce Merry asyncio: it’s all about the cancellation PyConZA 2017 5 / 5