Bugs item #1759997, was opened at 2007-07-24 17:58 Message generated for change (Comment added) made by nnorwitz You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1759997&group_id=5470
Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: Extension Modules Group: Python 2.5 Status: Open Resolution: None Priority: 5 Private: No Submitted By: Brian Warner (warner) Assigned to: Nobody/Anonymous (nobody) Summary: poll() on cygwin sometimes fails [PATCH] Initial Comment: While trying to track down a problem with our application (http://allmydata.org) running under cygwin, I discovered that the select.poll() object sometimes returns completely bogus data. poll() returns a list of tuples of (fd, revent), but fds are supposed to be small integers, and revents are a bitmask of POLLIN/POLLOUT flags. In my tests, I saw poll() return a list that started out looking normal, but the last half of the list contained fds and revents values like fd=0x7672a646, revent=0xd819. It turns out that under cygwin-1.5.24 (which I believe is a pretty recent version), the poll() call sometimes violates the POSIX specification, and provides a return value which is different than the number of pollfd structures that have non-zero .revents fields (generally larger). This causes the implementation of poll_poll() (in Modules/selectmodule.c) to read beyond the end of the pollfd array, copying random memory into the python list it is building, causing the bogus values I observed during my tests. These bogus values were mostly ignored, because the Twisted pollreactor that I was using noticed that the fd didn't correspond to any previously-registered file descriptor. It was only when the bogus fd happened to coincide with a real one (and when that indicated that a TCP listening socket became writable, which should never happen) that an exception was raised. The attached patch (against 2.5.1) works around the problem by manually counting the number of non-zero .revents, rather than relying upon the return value from poll(). This version passes test_poll on both linux and cygwin. cheers, -Brian Warner ---------------------------------------------------------------------- >Comment By: Neal Norwitz (nnorwitz) Date: 2007-07-24 22:53 Message: Logged In: YES user_id=33168 Originator: NO Has this problem been reported to cygwin? Have they fixed the problem? ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1759997&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
