New submission from Eric Hohenstein <ehohenst...@imvu.com>:
This error is unfortunately difficult to reproduce. I've only seen it happen on
Windows XP running on a dual core VMWare VM. I haven't been able to reproduce
it on a non-VM system running Windows 7. The only way I've been able to
reproduce it is to run the following unit test repeatedly on the XP VM
repeatedly until it fails:
import unittest
import urllib2
class DownloadUrlTest(unittest.TestCase):
def testDownloadUrl(self):
opener = urllib2.build_opener()
handle = opener.open('http://localhost/', timeout=60)
handle.info()
data = handle.read()
self.assertNotEqual(data, '')
if __name__ == "__main__":
unittest.main()
This unit test obviously depends on a web server running on localhost. In the
test environment where I was able to reproduce this problem the web server is
Win32 Apache 2.0.54 with mod_php. When the test fails, it fails with Windows
error code 10035 (WSAEWOULDBLOCK) being generated by the call to the recv()
method rougly once every 50-100 times the test is run. The following is a the
final entry in the stack when the error occurs:
File "c:\slave\h05b15\build\Ext\Python26\lib\socket.py", line 353, in read
(self=<socket._fileobject ...03B78170>, size=1027091)
data = self._sock.recv(left)
The thing to note is that the socket is being created with a timeout of 60. The
implementation of the socket.recv() method in socketmodule.c in the _socket
import module is to use select() to wait for a socket to become readable for
socket objects with a timeout and then to call recv() on the socket only if
select() did not return indicating that the timeout period elapsed without the
socket becoming readable. The fact that Windows error code 10035
(WSAEWOULDBLOCK) is being generated in the sock_recv_guts() method in
socketmodule.c indicates that select() returned without timing out which means
that Windows must have indicated that the socket is readable when in fact it
wasn't. It appears that there is a known issue with Windows sockets where this
type of problem may occur with non-blocking sockets. It is described in the
msdn documentation for WSAAsyncSelect()
(http://msdn.microsoft.com/en-us/library/ms741540%28VS.85%29.aspx). The code
for socketmodule.c doesn't seem to hand
le this type of situation correctly. The patch I've included with this issue
report retries the select() if the recv() call fails with WSAWOULDBLOCK (only
if MS_WINDOWS is defined). With the patch in place the test ran approximately
23000 times without failure on the system where it was failing without the
patch.
----------
components: IO, Windows
files: sock_recv.patch
keywords: patch
messages: 108770
nosy: ehohenstein
priority: normal
severity: normal
status: open
title: Error code 10035 calling socket.recv() on a socket with a timeout
(WSAEWOULDBLOCK - A non-blocking socket operation could not be completed
immediately)
type: behavior
versions: Python 2.6
Added file: http://bugs.python.org/file17780/sock_recv.patch
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue9090>
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