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List:       kde-devel
Subject:    Race Condition Issue with KJob and QNetworkAccessManager
From:       Adrián_Chaves_Fernández <adriyetichaves () gmail ! com>
Date:       2013-03-04 21:29:24
Message-ID: 1840940.J3BGlcHquk () afonso
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Hi,

There is not much I can add to what I already posted here: \
https://forum.kde.org/viewtopic.php?f=64&t=110250

Last Saturday I was trying to fix a test in libmediawiki. After several hours (12, \
I'm ashamed to admit) the only thing I could come up is with a simple 6-file \
compilable example to reproduce the issue (see the forums post).

To sum things up, the test starts a thread that runs a QTcpServer on a certain port, \
and then executes (exec()) a KJob. The job sends a request to the server, and after \
processing the reply, it finishes. This procedure is repeated in the tests several \
times, with different data, to check the results. And it fails from time to time, \
with different combinations of data. The error, as it runs out, is not the server \
reply; it's that the server ocasionally gets a connection from the KJob twice — \
while the connection is requested from the job only once.

In my simplified example, I just create the job and the server thread in a loop, get \
the job to call the server, finally count the requests the server got, and start \
again. When the server gets more than one request in a loop, I print "WTF!". With \
10000 loops, I bet you get some WTF! just like I did.

I'm not too experienced in Qt/C++/KDE, so I actually don't know if the reason is a \
bug in Qt, a bug in KJob, a bad implementation of the FakeServer class, or that I \
just got it all wrong. I just hope any of you guys know or can figure it out from the \
example provided in the forums post, and can help me get past this.

Thanks,
Adrian

PS: I've considered not counting the server request in the test, or using a "sleep()" \
function (which might solve the problem), but we all now dirty solutions like these \
will eventually come back, hiding an actual bug that does not get tested properly, or \
increasing the time needed to run the batery of tests for no reason. Not to mention \
that those dirty solutions would likely hunt me in my dreams!

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