Description
Summary
We are trying to use tbb::parallel_for_each within a project compiled with gcc 9.4.0 within an Ubuntu 20.04 environment. We have been using C++17 and are moving to C++20. tbb was compiling correctly with C++17. However with C++20 we see build errors relating to missing std::random_access_iterator. I think this is due to a mistake in dealing with collections in development versions of C++20.
Specifically I think the problem is with an if-def in parallel_for_each.h:
#if __TBB_CPP20_PRESENT
...
#endif // __TBB_CPP20_PRESENT
I believe this should be:
#if __TBB_CPP20_CONCEPTS_PRESENT
...
#endif // __TBB_CPP20_CONCEPTS_PRESENT
Other if-def in this file use the second form to cope with the absence of concepts in development versions of C++20 for gcc 9.4.0. The first form is sufficient for non-development versions of C++20 but not early versions. Making this change fixes the build for me.
Version
#define TBB_VERSION_MAJOR 2021
#define TBB_VERSION_MINOR 13
#define TBB_VERSION_PATCH 0
Environment
Ubuntu 20.04 (within WSL)
gcc 9.4.0
It's probably just gcc that's important.
Observed Behavior
Trying to compile:
std::vector<SampleStruct> tasks;
...
tbb::parallel_for_each(tasks.begin(), tasks.end(), Invoker<SampleStruct>());
Build error:
.../vcpkg_installed/x64-ubuntu-20-04-release/include/oneapi/tbb/parallel_for_each.h:427:29: error: no member named 'random_access_iterator' in namespace 'std' [clang-diagnostic-error]
std::conditional_t<std::random_access_iterator<It>,
^
.../vcpkg_installed/x64-ubuntu-20-04-release/include/oneapi/tbb/parallel_for_each.h:427:52: error: 'It' does not refer to a value [clang-diagnostic-error]
std::conditional_t<std::random_access_iterator<It>,
^
.../vcpkg_installed/x64-ubuntu-20-04-release/include/oneapi/tbb/parallel_for_each.h:425:20: note: declared here
template <typename It>
^
.../vcpkg_installed/x64-ubuntu-20-04-release/include/oneapi/tbb/parallel_for_each.h:427:55: error: expected ';' after alias declaration [clang-diagnostic-error]
std::conditional_t<std::random_access_iterator<It>,
^
.../vcpkg_installed/x64-ubuntu-20-04-release/include/oneapi/tbb/parallel_for_each.h:428:55: error: expected unqualified-id [clang-diagnostic-error]
std::random_access_iterator_tag,
^
.../vcpkg_installed/x64-ubuntu-20-04-release/include/oneapi/tbb/parallel_for_each.h:435:5: error: no template named 'iterator_tag_dispatch_impl' [clang-diagnostic-error]
iterator_tag_dispatch_impl<typename move_iterator_dispatch_helper<It>::type>;
^
.../vcpkg_installed/x64-ubuntu-20-04-release/include/oneapi/tbb/parallel_for_each.h:501:83: error: no template named 'iterator_tag_dispatch' [clang-diagnostic-error]
template <typename Iterator, typename Body, typename Item, typename IteratorTag = iterator_tag_dispatch<Iterator>>
^
.../vcpkg_installed/x64-ubuntu-20-04-release/include/oneapi/tbb/parallel_for_each.h:629:9: error: too few template arguments for class template 'for_each_root_task' [clang-diagnostic-error]
for_each_root_task<Iterator, Body, ItemType> root_task(first, last, body, w_context, context);
^
.../vcpkg_installed/x64-ubuntu-20-04-release/include/oneapi/tbb/parallel_for_each.h:502:7: note: template is declared here
class for_each_root_task : public for_each_root_task_base<Iterator, Body, Item>
^
Expected Behavior
Clean build.
Steps To Reproduce
Sorry. I haven't checked this as vcpkg isn't supplying the latest version. It should be visible with the correct compiler gcc 9.4.0 with a simple test program:
#include <tbb/parallel_for_each.h>
void ParallelApplyFooToList( const std::vector<Item>& list ) {
parallel_for_each( list.begin(), list.end(), ApplyFoo() );
}