[Qt-interest] sockets and threads on linux

[Jason H]

Thiago and I respectfully disagree on our philosophy to use threads when using 
sockets.
He says never, and I say anything above the trivial.

The fully async behavior of Qt's implementation means you don't have to use 
threads. You can do just fine without them... in most cases. And you can do just 
fine when having a GUI in the same thread too.

I use threads anytime the request could take substantial CPU. For most types of 
network traffic, when there is significant I/O delay or trivial computation 
involved in the network data. There won't be a scalability issue. (Serving a 
file will wait on disks for the most part, or it'll all be in cache, either way, 
single thread is fine)

I however prefer to offer SSL/TLS everywhere, and having it multithreaded will 
help distribute the encryption load over all cores. My computations were lengthy 
in nature, could use compression if the client requested it. For light loads (< 
50 clients) I could serve at 80% to full speed. After that, it dropped off. My 
specs required I be able to service within specific time frames at higher loads, 
so I went multithreaded.

It's not much harder to make it multithreaded, so if I think I might want it, 
then I do it from the start. If you're new and want to just get it working, then 
it's not a mistake to keep it single threaded and cross that bridge when you 
come to it. 













________________________________
From: pmqt71 <pmqt71 at gmail.com>
To: Thiago Macieira <thiago at kde.org>; qt-interest at trolltech.com
Sent: Sun, February 13, 2011 6:24:32 PM
Subject: Re: [Qt-interest] sockets and threads on linux


 
Hi Thiago,
I'd like to make the thread solution working in order to better understand the 
related concepts with Qt.
It actually works on XP: threads, sockets, events... it's working very well with 
hundreds of clients.
 
Are you suggesting me to avoid threads with sockets for a 
performance/optimization issue? or do you know about a possible problem?
 
thanks
pm

 
2011/2/13 Thiago Macieira <thiago at kde.org>

On Sunday, 13 de February de 2011 17:42:06 pmqt71 wrote:
>> Hi all,
>> Hi Qt people, I hope the best for Qt and you!
>>
>> I have a tcp client server program working well on WinXP, but not on linux.
>>
>> MyTcpServer inherits from QTcpServer. the incomingConnection method creates
>> a new socket and moves it to a new thread. The socket is handled by
>> MyTcpSocket that inherits from QTcpSocket and implements the slots to manage
>> client's incoming data:
>
>Why? Why do you insist in using threads for networking I/O after I told you
>last week that you don't need to?
>
>Use the thread to do the actual processing of the data. Not for the
>networking.
>
>
>> On linux (Ubuntu 9.04 64bit) the readyRead signal is not fired. The
>> incomingConnection is completed with no error, the pSocket objects gets the
>> event ThreadChange related to the moveToThread operation. Nothing else.
>> How can I debug?
>> Qt 4.6.2
>
>First of all, upgrade.
>
>Second, debug the moveToThread call and check if the socket notifiers and the
>socket engine got moved to the other thread. While debugging moveToThread, you
>should be able to identify any children that got moved along with it.
>
>Alternatively, or in addition, you can also put some breakpoints or debugging
>information in the register and unregisterSocketNotifier functions in the event
>dispatcher classes (QEventDispatcherUNIX or QEventDispatcherGlib). You should
>see the socket notifier be registered for the main thread, unregistered, then
>re-registered in the other thread.
>
>--
>Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
> Senior Product Manager - Nokia, Qt Development Frameworks
>     PGP/GPG: 0x6EF45358; fingerprint:
>     E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4 5358
>
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>



      
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