QApplication::exec crashing while running a multithreaded application

[psadhukhan]

Thanks.
Can you please tell me what I need to check corresponding to threads.
Since the product was working perfectly fine in Qt3.x( I have verified that) I am at a loss as to what I need to check.
Sometimes I get in Qt4 (which I did not get in Qt3]
QPixmap:it is not safe to use pixmap outside GUI thread, so it probably points to some threading issue

One thing I wanted to notify is, we were also using QApplication::lock() in our code but since Qt4 has made QApplication::lock() obsolete, I used QMutex mutex(QMutex::Recursive) [lock/unlock] function
The reason for using Recursive was sometimes the code has a lock inside a lock [and as told was working in Qt3]

LOCK: //QApplication::lock
funcA();
UNLOCK;

funcA(){
LOCK:
...
UNLOCK:

[high_flyer]

Unfortunately its not something anyone who does not know the code can answer.
You have to read the Qt documentation in respect to the changes done between Qt3 and Qt4.
Threading was redone extensively in Qt4, and you really should read the threading section in Qt4 docs.
When you know how threading in Qt4 works, you might attempt to rewrite the old Qt3 code so that it will conform to Qt4.
http://doc.trolltech.com/4.4/threads.html

I also would think, you should not hope to finish such a task in one afternoon, for a "real" application.

[psadhukhan]

I have taken a look at the threading tutorial but I don't think I am doing anything that is prohibited.
Since the product follows a Java multithreaded AWT model, whereby the main AWT Java thread [actually linux posix thread as I am testing in linux-x86] is what will be making GUI calls and then there is an eventThread [another Java thread] which will initialize [create QApplication, does show() and exec()]. The main AWT thread will draw in the QImage backbuffer and the paintEvent() call will flush the QImage into QPaintDevice. This is the logic that I wanted to follow in Qt4
But, in Qt4 calls I am not sure why I am getting the crash as described above as soon as I call exec(). sm_performSaveYourself is a QT function which I don't have control on and so I am not sure why it will create a QString with wrong address [thereby creating segv]. Also, libSM.so and libICE.so are system lib I presume so there also I do not have a control

I also have checked my mutex logic. I am using QMutex and I have seen that if I use it wrongly, it shows deadlock from QMutex class. But I am not seeing any such problem in our product. Is there anyone who has seen this kind of crash and know about a possible solution or an area where to investigate?
I can send the code to anyone who is interested.
I am really stuck with this crash. PLease suggest some remedy