can I use MyClass& in Qt signal and slots?

Mozzie

I am curious, if I emit a signal with parameter MyClass& which is a stack variable from one thread and I receive this signal from another thread and use Qt::QueuedConnection, is there any problem? would it crash by memory access? if not , how did this work?

thank you very much!

JKSH

@Mozzie said in can I use MyClass& in Qt signal and slots?:

I am curious, if I emit a signal with parameter MyClass& which is a stack variable from one thread and I receive this signal from another thread and use Qt::QueuedConnection, is there any problem? would it crash by memory access? if not , how did this work?

If you emit const MyClass&, then Qt will copy the variable so that it can be safely used by the other thread. (You need to register your class first, using qRegisterMetaType(): https://doc.qt.io/qt-5/qmetatype.html#qRegisterMetaType )

Don't use a non-const reference between threads.

Mozzie

@JKSH said in can I use MyClass& in Qt signal and slots?:

@Mozzie said in can I use MyClass& in Qt signal and slots?:

I am curious, if I emit a signal with parameter MyClass& which is a stack variable from one thread and I receive this signal from another thread and use Qt::QueuedConnection, is there any problem? would it crash by memory access? if not , how did this work?

If you emit const MyClass&, then Qt will copy the variable so that it can be safely used by the other thread. (You need to register your class first, using qRegisterMetaType(): https://doc.qt.io/qt-5/qmetatype.html#qRegisterMetaType )

Don't use a non-const reference between threads.

thank you. So, if I use const MyClass& as paremeter, I can use it between threads?

JKSH

@Mozzie said in can I use MyClass& in Qt signal and slots?:

So, if I use const MyClass& as paremeter, I can use it between threads?

Yes (assuming that your class is allowed to be copied between threads).

JKSH

[Side discussion forked to https://forum.qt.io/topic/125858/passing-qobjects-across-threads-via-signals-and-slots ]