error: multiple definitions of sycl::helpers::negative_distance

[domantasjurkus]

I am trying to import <sycl/execution_policy> into my main.cpp file as well as a separate lib.cpp file, however I keep getting an internal SyclParallelSTL naming clash:

[ 80%] Building CXX object CMakeFiles/main.dir/main.cpp.o
[100%] Linking CXX executable main
liblib.a(lib.cpp.o):(.bss+0x0): multiple definition of `sycl::helpers::negative_distance'
CMakeFiles/main.dir/main.cpp.o:(.bss+0x0): first defined here
collect2: error: ld returned 1 exit status
CMakeFiles/main.dir/build.make:97: recipe for target 'main' failed
make[2]: *** [main] Error 1
CMakeFiles/Makefile2:100: recipe for target 'CMakeFiles/main.dir/all' failed
make[1]: *** [CMakeFiles/main.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2

The execution policy source code has a #ifndef __SYCL_EXECUTION_POLICY__ import guard, so I assume I can #include <sycl/execution_policy> in multiple files? The basic setup to reproduce the problem is below.

CMakeLists.txt:

# ...
# SYCL setup
#...
add_executable(main ${CMAKE_CURRENT_SOURCE_DIR}/main.cpp)
add_library (lib lib.cpp)
target_link_libraries(main PRIVATE lib)
add_sycl_to_target(main ${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/main.cpp)

main.cpp:

#include <vector>

#include <sycl/execution_policy>
#include <experimental/algorithm>

#include "lib.h"

int main() {
    std::vector<int> v = {3, 1, 5, 6};
    sycl::sycl_execution_policy<class sort> par;
    std::experimental::parallel::sort(par, v.begin(), v.end());

    reduction();

    return 0;
}

lib.cpp:

#include <sycl/execution_policy>
#include <experimental/algorithm>

void reduction() {
    std::vector<int> v = {3, 1, 5, 6};
    sycl::sycl_execution_policy<class reduce> par;
    int result = std::experimental::parallel::reduce(par, v.begin(), v.end(), 0, [](int acc, int e) { return acc + e; });
    std::cout << result << std::endl;
}

The corresponding problem can be found on this line. What I've tried is to add extern in front of the class definition, but that leads to negative_distance being undefined.

Any advice?