FindTBB does not work for 2021 and later versions.

[pnookala]

FindTBB.cmake fails with the below error for oneAPI versions later than 2021.

-- /opt/intel/oneapi/tbb/2021.6.0/env/..
CMake Error at cmake/modules/FindTBB.cmake:358 (file):
  file failed to open for reading (No such file or directory):

    /opt/intel/oneapi/tbb/2021.6.0/include/tbb/tbb_stddef.h
Call Stack (most recent call first):
  cmake/modules/FindCXXStdExecution.cmake:97 (find_package)
  CMakeLists.txt:114 (find_package)

Name of the version file has changed from tbb_stddef.h to version.h and the cmake module needs to be updated.

[devreal]

Maybe we should remove TBB from TTG. Or is any of our dependencies using that?

[pnookala]

MADNESS can be run using TBB or Parsec backends. May be it can be made optional?

[evaleev]

the only reason FindTBB is used in TTG is to implement parallel C++ algorithms on Linux, hence for examples only. We can get rid of it but we'd need to get rid of these examples ... I have an updated FindTBB that can handle OneAPI but some changes in TTG will be needed also...

[devreal]

Can we replace the use of tbb with the forall @evaleev wrote?

[evaleev]

the only use is in the ge_df example, but can't use forall there since the parallel std::for_each is used within the task. In fact it's probably a bad idea to use std::execution in such context anyway since its implementation details are not guaranteed by the standard. So I think we can remove this last use of std::execution and get rid of the need for TBB.