[Python-Dev] Socket timeout and completion based sockets

Glyph glyph at twistedmatrix.com
Mon Nov 26 20:23:55 CET 2012

On Nov 26, 2012, at 11:05 AM, Richard Oudkerk <shibturn at gmail.com> wrote:

> Using CancelIo()/CancelIoEx() to abort an operation started with WSARecv() does not seem to cause a problem

(emphasis mine)

Little command-line experiments are not the right way to verify the behavior of high-performance I/O APIs.  You need to do careful reading of the documentation, significant testing under load and experiments on a huge variety of platforms.  Windows runs in _lots_ of horrible, horrible places.

I think that the safest option would really be to better document the somewhat mangled state that a timeout may leave a socket in.  I don't believe the feature was intended for pipelined protocols; if you receive a timeout by using the stdlib timeout functionality you have generally burned the socket.

And, generally, things that care enough about performance or scalability enough to use IOCP operations should never use timeout-sockets anyway; it may do a select() internally (and on Windows, where poll() is never available, it _will_ do a select() internally), which limits the number of file descriptors you might even have in your process before you start encountering spurious errors.  The use case it supports is when you have a little tool that just needs to fetch a URL or something really simple, but wants to be able to get on with things if that doesn't work or takes too long.


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