QT plugins memory footprint and the debugger

[schouwen]

Hi,
I am (trying) to upgrade a qtquick application from qt 5.2 to qt 5.7. Now I am running in a bit unexpected problem. The application is quite large and contains 10+ modules that use the QTPluginLoader mechanism to load its functionality. It worked fine under 5.2 but under 5.7 I get memory issues when loading the plugins. Smaller plugins load fine, bigger ones bug out with a bad_alloc. Now I am using the MingGW compiler and this generates debug plugins which can grow quite big, 50+ Mb. Note that the problem disappears when I shrink the size of a plugin (removing functionality) and is happening purely in the qt code. I traced it down to the attempt of the pluginloader to read the whole plugin at once in one chunck of memory at which point it (can) generates a bad_alloc.
Of course I can split up my plugins but I was wondering if this is a real limitation or that I have to search elsewhere for the cause of this problem

[SGaist]

Hi and welcome to devnet,

Interesting question. Since it's bit lower level, I'd recommend bringing this to the interest mailing list. You'll find there Qt's developers/maintainers. This forum is more user oriented.

[schouwen]

@SGaist I will do that

[kshegunov]

@schouwen said in QT plugins memory footprint and the debugger:

which can grow quite big, 50+ Mb

I'd bet my head you have tons of resources inside those. That is enormous, the whole of the QtCore or the QtGui is that size. My advice - reduce the plugins' size. Compile the resources as external files and not into the binary.

[schouwen]

Its the way MIngw creates its debug code. It puts it inside the the dll making it 20 times(or more) bigger then a release version. The relevant dll's (that causes a problem) have in fact no resources. It is pure algorithms. MS puts the bulk of debug stuff outside the dll making its size more managable.