Qt-interest Archive, April 2007
Qt 4.2.2 and memory problems
Message 1 in thread
Hi,
I am writing a small serverless chat and file sharing application for my
local lan. Im this application, obviously I need to open a lot of windows
and sockets, etc. In such a situation, handling the deletion of all such
objects when their job is over is a very difficult task for me. Is there a
way to specify automatic deletion of QTcpSocket, QWidget, QStringList,
etc. when some event occurs?
I also ran into problems when the destructor gets called while in some
other thread, execution of a member function is going on. I just put an
'integer' variable called 'lock' to stop the destructor call till we're
executing in a function, is there a better way of locking?
Even QPixmaps use up a lot of memory if constructed every time you need an
icon. Finally I had to include a data member as a QPixmap in order to
avoid frequent creation. Is there a way to ensure that the memory used by
the pixmap gets cleared once its no longer in use?
In short, I just want to understand how can I manage my memory more
efficiently for my application.
Regards,
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Message 2 in thread
> I also ran into problems when the destructor gets called while in some
> other thread, execution of a member function is going on. I just put an
> 'integer' variable called 'lock' to stop the destructor call till we're
> executing in a function, is there a better way of locking?
YES! Use QThread::wait() in the destructors of your threads. That way the
destructor will finish whenever QThread::run() comes to an end. Of course
you have to come up with a way to quit the run() method. This way you can
smoothly terminate your thread doing everything that needs to be done
first ;-)
Hope I got your question right :)
Regards,
Malte
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Message 3 in thread
> YES! Use QThread::wait() in the destructors of your threads. That way the
> destructor will finish whenever QThread::run() comes to an end. Of course
> you have to come up with a way to quit the run() method. This way you can
> smoothly terminate your thread doing everything that needs to be done
> first ;-)
I didn't create any explicit threads in the code. I have a QTimer to a
function for remove all sockets that are done with their job.
Unfortunately, even after completion of the job, the socket class does
some cleanup activities. When it is doing so, the cleanup function calls
delete for that object, and causes segmentation faults. Now, I do a
locked++ in the beginning of every member function and locked-- before
exiting. So, I avoid calling delete for objects which have locked>0. Is
there a better way?
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Message 4 in thread
> I didn't create any explicit threads in the code. I have a QTimer to a
> function for remove all sockets that are done with their job.
> Unfortunately, even after completion of the job, the socket class does
> some cleanup activities. When it is doing so, the cleanup function calls
> delete for that object, and causes segmentation faults. Now, I do a
> locked++ in the beginning of every member function and locked-- before
> exiting. So, I avoid calling delete for objects which have locked>0. Is
> there a better way?
I have a hard time understanding what you are doing exactly. Is it
possible for you to post some code snipplets or some pseudo-code?
Regards,
Malte
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Message 5 in thread
> I have a hard time understanding what you are doing exactly. Is it
> possible for you to post some code snipplets or some pseudo-code?
Ok, its like this. There are two classes, Communicator and ClientHandler.
Communicator is like a central controlling thing. It has a QTimer that
calles 'refreshCommunication' function. Communicator is derived from
QTcpServer. It listens for new clients, when a new one connects, it
creates a 'ClientHandler' object to handle it. All these ClientHandler
objects are appeneded to a QList in Communicator.
Now, the 'refreshCommunication' function goes through the QList of
ClientHandler objects and calls 'delete' for those which have status as
'H_DONE' or 'H_ERROR'.
In ClientHandler, if the job is done successfully, it sets status as
H_DONE and for error, H_ERROR. Now, when ClientHandler is carrying out
exection of some member function (after it has set the status to be
'done' or 'error'), the 'refreshCommunication' function calls destructor
and then all subsequent operations in ClientHandler's currently executing
member function fail/seg fault.
I added a data member 'locked' in ClientHandler (init to 0). While
entering any member function, I do locked++ and on returning locked--.
This way, in 'refreshCommunication' I don't delete those ClientHandler
objects having locked>0.
Is there a better way to lock ClientHandler, to somehow determine if any
of its member functions are currently under execution?
Hope now its clearer.
Regards,
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Message 6 in thread
> Is there a better way to lock ClientHandler, to somehow determine if any
> of its member functions are currently under execution?
The one thing that comes to mind is if your ClientHandlers are QObjects, you could
use "deleteLater()" on them to defer their deletion until after the event queue
clears up.
Caleb
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