[Qt-interest] QTcpSockets on Windows

[David Boosalis]

A problem keep showing up with QTcpSocket on Windows (Windows 7, Vista, and
XP).  And that is is that it starts to slow down.  I verify this in several
ways

1) I compare two laptops that are basically the same HP style laptop only
one has slightly more memory. One runs Kubuntu 10.4 the other WIndows
Vista.  They both are using a wired ethernet connection.    Given enough
time, the Windows machine will be from three seconds to a minute behind  the
Linux machine.

2)  We have a third party client application that we run on the same Windows
machine mentioned above it stays current.  The third party application does
not use Qt.


I am using Qt 4.6.2 now and have seen the same behavior with Qt 4.6.1.  I
did not see any changes in the release notes on 4.6.3 to QTcpSocket to lead
me to assume a Qt upgrade would fix the problem.  The server code also
written with QT and using QTcpServer send out a 100 byte packet every
second.  I have check the cpu usage and network levels both of which are
very low on all clients and server, so I know I am not bound by either of
those.

I have started to try and get some diagnostics using WireShark.  I noted
that on the Windows machine I get a lot more red "TCP RST" messages, at
least twice(more like three times)  as much then what I see on Linux  I am
in the process of trying to decipher it. Wireshark on windows also reports a
"TCP Port numbers reused" quite often.

The only flag I have set thus far is the NODELAY.  Does anyone know of
another flag I can set to improve performance on Windows.   Any info on
QTcpSocket improvements in QT4.6.3 or even what will be 4.7 also welcomed.

Thank you
David
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