Crash in QDateTime::currentDateTime().toString()

marcus.fr

Hi

I use QDateTime::currentDateTime() function in multiple threads. In each thread I create new QDateTime object on which I call currentDateTime().toString(). A crash happened and debbuger pointed to globalQDateTime.currentDateTime().toString(). I tried hundreds times but cannot reproduce the crash again. I cannot stop thinking what was the cause of the crash. QDateTime.currentDateTime is a static function and documentation says all functions in the QDateTime class are reentrant. As far as I know it is safe to use static function in secondary threads as long as it is a part of a new object instantiated in those threads. Any help please.

@//Main Thread:
QDateTime globalQDateTime;
globalQDateTime.currentDateTime().toString(); // crash here

//Thread 1:
QDateTime tQDateTime; tQDateTime.daysTo(tQSslCertificate.expiryDate());

//Thread 2:
QDateTime tQDateTime;
if (mQDateTime.addSec(3000) > tQDateTime.currentDateTime() ) ...@

tucnak

What signal does it throw? SIGSEGV?

marcus.fr

[quote author="tucnak" date="1339400575"]What signal does it throw? SIGSEGV?[/quote]

I didn't saved the debug log. The problem is I cannot replicate it now. I'll do my best to cause the crash again and will post back complete results.

Jeroentjehome

Hi, the toString returns a QString so maybe you didn't handle the QString returned properly. That might also cause the segment error?
The threads may not be the problem.
greetz

soundar

Try to use this link.It gives the solution for problem
http://qt-project.org/doc/qt-4.8/qdatetime.html

tucnak

[quote author="Jeroentje@home" date="1339426002"]Hi, the toString returns a QString so maybe you didn't handle the QString returned properly. That might also cause the segment error?
The threads may not be the problem.
greetz[/quote]

What are you talking about?! Ignoring return value of member function is legal! Absolutely legal in C++ meaning.

miroslav

ENEEDMOREINFO. Could you post a stack trace of the crash? The code looks fine.

What I am not sure about is whether currentDateTime() is thread safe. If it uses a static object on QDateTime, it probably is not. You would need to serialize access to it then.

shanek

currentDateTime is thread safe if your system has localtime_r (or is windows)
localtime is used if localtime_r is not available, and that may not be thread safe (depending on libc implementation)

miroslav

That is really good to know. Is it actually documented somewhere? If not, we can add it to a doc note.

shanek

QDateTime is documented as being re-entrant.
It requires the C library to be re-entrant to achieve that though.
(either by providing the posix thread safe functions or by implementing the standard functions in a thread safe manner)