龙卷风发生器引擎中的内存泄漏,当连接关闭时使用try/finally块

Question

这个很棒的代码,显示龙卷风gen模块中的内存泄漏,当连接关闭而不读取响应时:

import gc
from tornado import web, ioloop, gen

class MainHandler(web.RequestHandler):
    @web.asynchronous
    @gen.engine
    def get(self):
        gc.collect()
        print len(gc.garbage)  # print zombie objects count
        self.a = '*' * 500000000  # ~500MB data
        CHUNK_COUNT = 100
        try:
            for i in xrange(CHUNK_COUNT):
                self.write('*' * 10000)  # write ~10KB of data
                yield gen.Task(self.flush)  # wait for reciever to recieve
            print 'finished'
        finally:
            print 'finally'

application = web.Application([
    (r"/", MainHandler),
    ])

application.listen(8888)
ioloop.IOLoop.instance().start()

现在,多次运行一个简单的测试客户端

#!/usr/bin/python
import urllib
urlopen('http://127.0.0.1:8888/')  # exit without reading response

现在,服务器输出显示增量内存使用情况:

0
WARNING:root:Write error on 8: [Errno 104] Connection reset by peer
1
WARNING:root:Read error on 8: [Errno 104] Connection reset by peer
WARNING:root:error on read
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/iostream.py", line 361, in _handle_read
    if self._read_to_buffer() == 0:
  File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/iostream.py", line 428, in _read_to_buffer
    chunk = self._read_from_socket()
  File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/iostream.py", line 409, in _read_from_socket
    chunk = self.socket.recv(self.read_chunk_size)
error: [Errno 104] Connection reset by peer
2
ERROR:root:Uncaught exception GET / (127.0.0.1)
HTTPRequest(protocol='http', host='127.0.0.1:8888', method='GET', uri='/', version='HTTP/1.0', remote_ip='127.0.0.1', body='', headers={'Host': '127.0.0.1:8888', 'User-Agent': 'Python-urllib/1.17'})
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/web.py", line 1021, in _stack_context_handle_exception
    raise_exc_info((type, value, traceback))
  File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/web.py", line 1139, in wrapper
    return method(self, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/gen.py", line 120, in wrapper
    runner.run()
  File "/usr/local/lib/python2.7/dist-packages/tornado-2.4.1-py2.7.egg/tornado/gen.py", line 345, in run
    yielded = self.gen.send(next)
  File "test.py", line 10, in get
    self.a = '*' * 500000000
MemoryError
ERROR:root:500 GET / (127.0.0.1) 3.91ms

如果设置CHUNK_COUNT为1,则可将10KB数据写入OS连接缓冲区,并将"完成"和"最终"文本打印到控制台,并且由于生成器已完成,因此不会发生内存泄漏.

但奇怪的是,如果你删除try/finally块,问题就会消失!(即使CHUNK_COUNT设置为100)

这是CPython或龙卷风上的错误还是......？!

Answer 1

该错误使用 Tornado 2.4.1（提出此问题时的最新版本）进行了测试，并在https://github.com/facebook/tornado/issues/660上报告。

该问题已在提交https://github.com/facebook/tornado/commit/769bc52e11656788782a6e7a922ef646503f9ab0中修复，并包含在 Tornado 3.0 中。