Using Twisted + Cyclone + PyPy to handle POST requests cause a memory leak?

Question

After a lot of investigating, I found out that after serving hundreds of thousands of HTTP POST requests, there's a memory leak. The strange part is that the memory leak only occurs when using PyPy.

Here's an example code:

from twisted.internet import reactor
import tornado.ioloop

do_tornado = False
port = 8888

if do_tornado:
    from tornado.web import RequestHandler, Application
else:
    from cyclone.web import RequestHandler, Application

class MainHandler(RequestHandler):
    def get(self):
        self.write("Hello, world")

    def post(self):
        self.write("Hello, world")

if __name__ == "__main__":
    routes = [(r"/", MainHandler)]
    application = Application(routes)

    print port
    if do_tornado:
        application.listen(port)
        tornado.ioloop.IOLoop.instance().start()
    else:
        reactor.listenTCP(port, application)
        reactor.run()

Here is the test code I am using to generate requests:

from twisted.internet import reactor, defer
from twisted.internet.task import LoopingCall

from twisted.web.client import Agent, HTTPConnectionPool
from twisted.web.iweb import IBodyProducer

from zope.interface import implements

pool = HTTPConnectionPool(reactor, persistent=True)
pool.retryAutomatically = False
pool.maxPersistentPerHost = 10
agent = Agent(reactor, pool=pool)

bid_url = 'http://localhost:8888'

class StringProducer(object):
    implements(IBodyProducer)

    def __init__(self, body):
        self.body = body
        self.length = len(body)

    def startProducing(self, consumer):
        consumer.write(self.body)
        return defer.succeed(None)

    def pauseProducing(self):
        pass

    def stopProducing(self):
        pass


def callback(a):
    pass

def error_callback(error):
    pass

def loop():
    d = agent.request('POST', bid_url, None, StringProducer("Hello, world"))
    #d = agent.request('GET', bid_url)
    d.addCallback(callback).addErrback(error_callback)


def main():
    exchange = LoopingCall(loop)
    exchange.start(0.02)

    #log.startLogging(sys.stdout)
    reactor.run()

main()

Note that this code does not leak with CPython nor with Tornado and Pypy! The code leaks only when using Twisted and Pypy together, and ONLY when using a POST request.

To see the leak, you have to send hundreds of thousands of requests.

Note that when setting PYPY_GC_MAX, the process eventually crashes.

What's going on?

Answer 1

Turns out that the cause of the leak is the BytesIO module.

Here's how to simulate the leak on Pypy.

from io import BytesIO
while True: a = BytesIO()

Here's the fix: https://bitbucket.org/pypy/pypy/commits/40fa4f3a0740e3aac77862fe8a853259c07cb00b