Why is moc slow for some classes?
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@artwaw I have not measured, but the files that are slow are all similar and there are a few thousands other files on the project, which mostly take about 0.5-0.6 sec to parse, so it seems unlikely to be caused by I/O. (and obviously this is reproducible, it's not one time measurement)
@J.Hilk It is a possibility I'm considering, but we still use some other features of metaObject(), so it would require a little more effort.
@Dan-Princ Thanks for clarifying that. My next check would be internal includes, maybe there is a loop somewhere?
Please note though that I never experienced that kind of problems before and perform a logical guess here. -
Since I haven't figured out much more about this problem, I removed the Q_OBJECT macro from these classes. Not the best solution, but the only one I know of...
Hi
moc does not expand templates. its not a compiler.I tried a few combinations but I could not make moc hang/be slow on any files.
Do you have a concrete example that compiles and is known to take extra time?
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Hi
moc does not expand templates. its not a compiler.I tried a few combinations but I could not make moc hang/be slow on any files.
Do you have a concrete example that compiles and is known to take extra time?
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@mrjj Unfortunately not, I can't share the code that does it and it's not happening if I try to create some minimal example...
@Dan-Princ
ok, i understand.I did try with some class with lots of base classes but saw no effect.
Only by make extremely large .h file i could get time up but it sounds your case
is different. -
@mrjj Unfortunately not, I can't share the code that does it and it's not happening if I try to create some minimal example...
@Dan-Princ Just an idea: do you include many header files which include other header files and so on?
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@Dan-Princ Just an idea: do you include many header files which include other header files and so on?
@jsulm Well if I compile the file with /showIncludes, it prints ~3800 includes (mostly from libraries - 2600 from boost, 500 from Qt). If I run preprocessor on the header file, it has about 780000 lines. But I don't know how relevant it is as these numbers will be similar for most of the files I think...
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@jsulm Well if I compile the file with /showIncludes, it prints ~3800 includes (mostly from libraries - 2600 from boost, 500 from Qt). If I run preprocessor on the header file, it has about 780000 lines. But I don't know how relevant it is as these numbers will be similar for most of the files I think...
@Dan-Princ said in Why is moc slow for some classes?:
- 2600 from boost
Boost is a template library (mostly) and as any template library is notorious for terrible compilation times, which is a consequence of how templates work.
it has about 780000 lines
And you have your answer. That's a huge file to parse.
And by the way, as @mrjj already said, you can't mix templates andQObject. -
@Dan-Princ said in Why is moc slow for some classes?:
- 2600 from boost
Boost is a template library (mostly) and as any template library is notorious for terrible compilation times, which is a consequence of how templates work.
it has about 780000 lines
And you have your answer. That's a huge file to parse.
And by the way, as @mrjj already said, you can't mix templates andQObject.@kshegunov That's a huge file to parse, true, but there are many other files that have similar (500000) number of lines after preprocessor and moc takes 0.6sec. So I'm not sure this is the main factor.
You can't put Q_OBJECT inside a template, but AFAIK you can have templated base class.
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@kshegunov That's a huge file to parse, true, but there are many other files that have similar (500000) number of lines after preprocessor and moc takes 0.6sec. So I'm not sure this is the main factor.
You can't put Q_OBJECT inside a template, but AFAIK you can have templated base class.
@Dan-Princ said in Why is moc slow for some classes?:
You can't put Q_OBJECT inside a template, but AFAIK you can have templated base class.
Yes if it doesn't derive from
QObjectyou can do something like:class A : public QObject, public MyTemplatedClass< ... > //< QObject derived class always goes first! { };But even then it's rather clumsy.
QObjectdoesn't play well with templates.
