gevent network library Denis Bilenko gevent org Problem

gevent network library Denis Bilenko gevent. org

Problem statement from urllib 2 import urlopen response = urlopen('http: //gevent. org') body = response. read() How to manage concurrent connections?

Problem statement Possible answer: Async framework (Twisted, asyncore, . . . ) def on_response_read(response): d = response. read() d. add. Callbacks(on_body_read, on_error) def on_error(error): . . . def on_body_read(body): . . . d = read. URL('http: //gevent. org'). d. add. Callbacks(on_response_read, on_error) reactor. run()

simplicity is lost

Problem statement Possible answer: Threads from threading import Thread def read_url(url): response = urllib 2. urlopen(url) body = response. read() t 1=Thread(target=read_url, args=('http: //gevent. org', )) t 1. start() t 2=Thread(target=read_url, args=('http: //python. org', )) t 2. start() t 1. join() t 2. join()

resource hog

Memory required for 10 k connections threading 400 MB twisted 55 MB

gevent (greenlet + libevent) from gevent import monkey; monkey. patch_all() def read_url(url): response = urllib 2. urlopen(url) body = response. read() a = gevent. spawn(read_url, 'http: //gevent. org') b = gevent. spawn(read_url, 'http: //python. org') gevent. joinall([a, b])

concurrent fetch

Memory required for 10 k connections threading 400 MB twisted 55 MB gevent 70 MB

greenlet

from greenlet import greenlet >>> def myfunction(arg): . . . return arg + 1 >>> g = greenlet(myfunction) >>> g. switch(2) 3

from greenlet import greenlet >>> MAIN = greenlet. getcurrent() >>> def myfunction(arg): . . . MAIN. switch('hello'). . . return arg + 1 >>> g = greenlet(myfunction) >>> g. switch(2) 'hello' >>> g. switch('hello to you') 3

switching deep down the stack >>> def myfunction(arg): . . . MAIN. switch('hello'). . . return arg + 1 >>> def top_function(arg): . . . return myfunction(arg) >>> g = greenlet(top_function) >>> g. switch(2) 'hello'

from greenlet import greenlet • • primitive pseudothreads, share same OS thread switched explicitly via switch() and throw() organized in a tree, each has. parent except MAIN switch(), throw() and. parent reserved for gevent http: //codespeak. net/py/0. 9. 2/greenlet. html

How gevent uses greenlet MAIN HUB spawned greenlets

Hub: greenlet that runs event loop from gevent import core class Hub(greenlet): def run(self): core. dispatch() # wrapper for event_dispatch() def get_hub(): # return the global Hub instance # creating one if does not exist gevent/hub. py

Event loop • libevent 1. 4. x or 2. 0. 5 -beta • gevent. core: wraps libevent API (like pyevent) >>> def print_hello(): . . . print 'hello' >>> gevent. core. timer(1, print_hello) <timer. . . > >>> gevent. core. dispatch() hello 1 # return value (no more events)

Implementation of gevent. sleep() def sleep(seconds=0): """Put the current greenlet to sleep""“ switch = getcurrent(). switch timer = core. timer(seconds, switch) try: get_hub(). switch() finally: timer. cancel()

Cooperative socket • gevent. socket: compatible synchronous interface • wraps a non-blocking socket def recv(self, size): while True: try: return self. _sock. recv(size) except error, ex: if ex[0] == EWOULDBLOCK: wait_read(self. fileno()) else: raise

Cooperative socket • gevent. socket: compatible synchronous interface • wraps a non-blocking socket def wait_read(fileno): switch = getcurrent(). switch event = core. read_event(fileno, switch) try: get_hub(). switch() finally: event. cancel() gevent/socket. py

Cooperative socket • gevent. socket • dns queries are resolved through libevent-dns (getaddrinfo, gethostbyname) • gevent. ssl

Monkey patching from gevent import monkey; monkey. patch_all() def read_url(url): response = urllib 2. urlopen(url) body = response. read() a = gevent. spawn(read_url, 'http: //gevent. org') b = gevent. spawn(read_url, 'http: //python. org') gevent. joinall([a, b])

Monkey patching Patches: • socket and ssl modules • time. sleep, select • thread and threading Beware: • libraries that wrap C libraries (e. g. My. SQLdb) • Disk I/O • things not yet patched: subprocess, os. system, sys. stdin Tested with httplib, urllib 2, mechanize, mysql-connector, SQLAlchemy, . . .

Greenlet objects from gevent import monkey; monkey. patch_all() def read_url(url): response = urllib 2. urlopen(url) body = response. read() a = gevent. spawn(read_url, 'http: //gevent. org') b = gevent. spawn(read_url, 'http: //python. org') gevent. joinall([a, b])

Greenlet objects def read_url(url): response = urllib 2. urlopen(url) body = response. read() g = Greenlet(read_url, url) g. start() = spawn # wait for it to complete g. join() # or raise an exception and wait to exit g. kill()

Greenlet objects def read_url(url): response = urllib 2. urlopen(url) body = response. read() g = Greenlet(read_url, url) g. start() = spawn # wait for it to complete (or timeout expires) g. join(timeout=2) # or raise and wait to exit (or timeout expires) g. kill(timeout=2)

Timeouts with gevent. Timeout(5): response = urllib 2. urlopen(url) for line in response: print line # raises Timeout if not done after 5 seconds with gevent. Timeout(5, False): response = urllib 2. urlopen(url) for line in response: print line # exits block if not done after 5 seconds Beware: catch-all “except: ”, non-yielding code

API • socket, ssl • Greenlet • Timeout • Event, Async. Result • Queue (also Joinable. Queue, Priority. Queue, Lifo. Queue) – Queue(0) is a synchronous channel • Pool • Stream. Server: TCP and SSL servers • WSGI servers

WSGI servers • gevent. wsgi – uses libevent-http – efficient, but lacks important features • gevent. pywsgi – uses gevent sockets • green unicorn (gunicorn. org) – its own parser or gevent’s server – pre-fork workers

Caveat emptor • Reduced portability – no Jython, Iron. Python – not all platforms supported by CPython • Py. Thread. State is shared – exc_info (saved/restored by gevent) – tracing, profiling info

Future plans • http: //code. google. com/p/gevent/issues/list • alternative coroutine libraries – Stackless – swapcontext • more libevent: – http client – buffered socket operations – priorities • process handling (gevent. subprocess) • even more stable API with 1. 0

Examples • • bitbucket. org/denis/gevent/src/tip/examples/ chat. gevent. org omegle. com Projects. Using. Gevent – gevent-mysql – psycopg 2 • bit. ly/use-gevent – websockets, web crawlers, facebook apps

Summary • • • coroutines are easy-to-use threads as efficient as async libraries works well if app is I/O bound simple API, many things familiar works with unsuspecting 3 rd party modules

Thank you! gevent. org @gevent