[Interest] QtCreator annoying message

Adam Light aclight at gmail.com
Tue Feb 16 19:33:07 CET 2021

On Tue, Feb 16, 2021 at 7:12 AM Alexander Dyagilev <alervdvcw at gmail.com>

> I always appears after i had to restart Qt Creator.
> I had to restrt it due to the following reasons:
> 1) It stops parsing c++ code for opened files so i can't use IDE's C++
> support
> 2)
> ...
> I can't think of another reason. It's always 1st one.
I see this all the time on Windows with our application's project (hundreds
of files, several million lines of code, likely very poorly organized with
regards to headers). When the "Parsing C/C++ Files" step starts (eg.
after switching between debug and release configurations), it typically
takes 10+ minutes (if it even finishes at all), and I think the message you
described will show up if I kill Creator while it's parsing C/C++ files.
For reference, a complete build of our project from scratch takes about 2
minutes on the same machine, so clearly the files can be parsed much more
quickly by the actual compiler.

My machine has 16 cores/32 threads. If I collect ETW data while Creator is
parsing files, the parsing is happening in around 20 threads but the total
CPU utilization during the entire time is typically about 5%, suggesting
that there may be a lot of thread contention. If I dive deeper into the
traces, for a 21.4 s sampling period (which represents 25.1 s of
qtcreator.exe CPU time), 18.2 seconds of CPU time are spent in either
RtlpAllocateHeap or RtlpHeapFindListLookupEntry. These are Windows API
functions that are indirectly called by QVector::realloc. In this case,
most of that is due to <CPlusPlus::Internal::PPToken>::realloc. Note that
this 21.4 s sampling period is just a small part of the ~10 minutes it took
to complete the Parsing C/C++ Files step.

My guess is that Creator's CppTools and CPlusPlus plugins are not able to
efficiently handle deep #include trees. For what it's worth, our project
uses precompiled headers and in Creator's Code Model settings tab, "Ignore
precompiled headers" is unchecked.

I can't provide our project since our application is not open source. If
there is any sort of debugging mode I can enable that might shed more light
on what is happening I'm happy to help there.

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