Trying to use C++17 parallel algorithms with Qt

Eukaryote

Hi
I'm trying to use C++17 parallel algorithms with Qt5.15. I'm using GCC9.3 on CentOS 7.0
I've installed oneapi-tbb-2021.1.1,
added

export CPATH=<tbb_install_path>/oneapi-tbb-2021.1.1/include:<tbb_install_path>/oneapi-tbb-2021.1.1/include/oneapi:<tbb_install_path>/oneapi-tbb-2021.1.1/include/oneapi/tbb
export LD_LIBRARY_PATH=<tbb_install_path>/oneapi-tbb-2021.1.1/lib/intel64/gcc4.8:$LD_LIBRARY_PATH

When I'm trying to compile cpp file with #include <execution> has error:

<tbb_install_path>/oneapi-tbb-2021.1.1/include/oneapi/tbb/profiling.h:231:22: error: expected unqualified-id before 'const'
  231 |     static void emit(const std::string &) { }
      |                      ^~~~~
<tbb_install_path>/oneapi-tbb-2021.1.1/include/oneapi/tbb/profiling.h:231:22: error: expected ')' before 'const'
  231 |     static void emit(const std::string &) { }
      |                     ~^~~~~
      |                      )

I suspect this is caused by "emit" name clashing with Qt emit. How can I solve this issue?
Thank you.

sierdzio

Use CONFIG+=no_keywords in your qmake file: doc.

Eukaryote

@sierdzio said in Trying to use C++17 parallel algorithms with Qt:

no_keywords

Thank you very much for your reply.
From my understanding, this will require to change occurrences of signals to Q_SIGNALS and slots to Q_SLOTS in all of Qt code?
Is there a way to have some sort of "ignore list" for specific files?

I'll try this "fix-it" https://github.com/KDE/clazy/blob/master/docs/checks/README-qt-keywords.md see how that goes.

Thank you again

sierdzio

Yes, no_keywords will work globally for the whole project.

Locally I think you can just remove emit per file like this:

// in c++ code:
#undef emit

Eukaryote

Thank you very much again

Our build system doesn't use qmake and calls "moc" directly. I don't know where I can add CONFIG += no_keywords. How can I add this switch to "moc" without make?
I added indef as you suggested.
Now I'm getting the following error:

In file included from <install_dir>/gcc/v9.3.0/include/c++/9.3.0/pstl/parallel_backend.h:14,
                 from  <install_dir>/gcc/v9.3.0/include/c++/9.3.0/pstl/algorithm_impl.h:25,
                 from  <install_dir>/gcc/v9.3.0/include/c++/9.3.0/pstl/glue_execution_defs.h:52,
                 from  <install_dir>//gcc/v9.3.0/include/c++/9.3.0/execution:32,
                 from policies.hpp:21,
                 from bench_t.cpp:27:
 <install_dir>/gcc/v9.3.0/include/c++/9.3.0/pstl/parallel_backend_tbb.h: In function 'void __pstl::__par_backend::__cancel_execution()':
 <install_dir>/gcc/v9.3.0/include/c++/9.3.0/pstl/parallel_backend_tbb.h:70:10: error: 'tbb::task' has not been declared
   70 |     tbb::task::self().group()->cancel_group_execution();
      |          ^~~~
In file included from  <install_dir>/gcc/v9.3.0/include/c++/9.3.0/pstl/parallel_backend.h:14,
                 from  <install_dir>/gcc/v9.3.0/include/c++/9.3.0/pstl/algorithm_impl.h:25,
                 from  <install_dir>/gcc/v9.3.0/include/c++/9.3.0/pstl/glue_execution_defs.h:52,
                 from  <install_dir>/gcc/v9.3.0/include/c++/9.3.0/execution:32,

Is "task" some sort of special keyword too or it can't find correct headers?

sierdzio

I don't think task is a keyword.

Our build system doesn't use qmake and calls "moc" directly. I don't know where I can add CONFIG += no_keywords. How can I add this switch to "moc" without make?

Add QT_NO_KEYWORDS to compiler defines (-DQT_NO_KEYWORDS). This has nothing to do with moc.

Eukaryote

@sierdzio said in Trying to use C++17 parallel algorithms with Qt:

QT_NO_KEYWORDS

From your link to the docs: "CONFIG += no_keywords tells Qt not to define the moc keywords signals, slots, and emit, because these names will be used by a 3rd party library," so I assumed it's moc command.
Isn't it moc that translates all connection/slot related logic to C++ ?

Christian Ehrlicher

@Eukaryote said in Trying to use C++17 parallel algorithms with Qt:

Isn't it moc that translates all connection/slot related logic to C++ ?

It is, but the compiler generates the machine code.

Eukaryote

Just to summerise the issue in case anyone else will be encounter something similar.

I want to use <execution> header from C++17 with GCC9
That requires Intel's TBB library and includes
Both Qt and TBB use emit that is replaced by Qt. To solve this locally, I've undefined "emit" before using <execution> header. The general solution is to use -DQT_NO_KEYWORDS and replace emit/signal with Q_SIGNALS/ Q_SLOTS
gcc9 uses task class from TBB that was deprecated in 2020. The solution is to use TBB 2019 or a newer GCC.