How to implement a TBB input_node? - tbb

Question

Apparently in tbb::flow the source_node has been deprecated, and starting in the 2021.1 version we are only supposed to use input_node. Simply replacing the class does not seem to work, though. I have a working code using source_node in version 2020.3. If I try using input_node I get a cryptic message.
It seems input_node expects Body to implement a function that takes a flow_control object. Is this the case? Otherwise what is wrong here?
I cannot seem to be able to run any example codes with input_body.
====================[ Build | capybara | Debug-System ]==========================
/home/nicolau/bin/clion-2020.1.1/bin/cmake/linux/bin/cmake --build /home/nicolau/src/capybara/cmake-build-debug-system --target capybara -- -j 9
Scanning dependencies of target capybara
[ 50%] Building CXX object CMakeFiles/capybara.dir/main.cpp.o
In file included from /home/nicolau/src/oneapi-tbb-2021.1-beta08/include/tbb/flow_graph.h:345:0,
from /home/nicolau/src/capybara/main.cpp:9:
/home/nicolau/src/oneapi-tbb-2021.1-beta08/include/tbb/detail/_flow_graph_body_impl.h: In instantiation of ‘Output tbb::detail::d1::input_body_leaf<Output, Body>::operator()(tbb::detail::d1::flow_control&) [with Output = std::tuple<cv::Mat, std::chrono::time_point<std::chrono::_V2::system_clock, std::chrono::duration<long int, std::ratio<1, 1000000000> > > >; Body = main(int, char**)::<lambda(imgtv&)>]’:
/home/nicolau/src/capybara/main.cpp:424:1: required from here
/home/nicolau/src/oneapi-tbb-2021.1-beta08/include/tbb/detail/_flow_graph_body_impl.h:88:66: error: no match for call to ‘(main(int, char**)::<lambda(imgtv&)>) (tbb::detail::d1::flow_control&)’
Output operator()(flow_control& fc) override { return body(fc); }
^
/home/nicolau/src/capybara/main.cpp:350:58: note: candidate: main(int, char**)::<lambda(imgtv&)>
tbb::flow::input_node<imgtv> src(g, [&](imgtv &v) -> bool {
^~~~
/home/nicolau/src/capybara/main.cpp:350:58: note: no known conversion for argument 1 from ‘tbb::detail::d1::flow_control’ to ‘imgtv& {aka std::tuple<cv::Mat, std::chrono::time_point<std::chrono::_V2::system_clock, std::chrono::duration<long int, std::ratio<1, 1000000000> > > >&}’
CMakeFiles/capybara.dir/build.make:82: recipe for target 'CMakeFiles/capybara.dir/main.cpp.o' failed
make[3]: *** [CMakeFiles/capybara.dir/main.cpp.o] Error 1
CMakeFiles/Makefile2:95: recipe for target 'CMakeFiles/capybara.dir/all' failed
make[2]: *** [CMakeFiles/capybara.dir/all] Error 2
CMakeFiles/Makefile2:102: recipe for target 'CMakeFiles/capybara.dir/rule' failed
make[1]: *** [CMakeFiles/capybara.dir/rule] Error 2
Makefile:138: recipe for target 'capybara' failed
make: *** [capybara] Error 2

Answer 1

Apparently the interface has changed compared to source_node, and the function is now supposed to take a flow_control reference and return the new input object as output.
https://github.com/oneapi-src/oneTBB/issues/270#issuecomment-683645172