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# Ideas come from
#
# https://gitlab.kitware.com/cmake/cmake/-/issues/17834
#
# But applied to the use of libatomic instead of libstdc++fs.
# The need to do this was highlighted as part of:
# https://github.com/PelicanPlatform/xrootd-s3-http/pull/81
# The original driving use case was 32-bit builds; if we
# decide to drop those, we can rip out the target
include(CheckSourceCompiles)
function( check_working_cxx_atomics varname )
CHECK_SOURCE_COMPILES( CXX "
#include <cstdlib>
#include <atomic>
#include <cstdint>
int main() {
std::atomic<uint8_t> a1;
std::atomic<uint16_t> a2;
std::atomic<uint32_t> a3;
std::atomic<uint64_t> a4;
return a1++ + a2++ + a3++ + a4++;
}" ${varname}
)
endfunction( check_working_cxx_atomics varname )
check_working_cxx_atomics( CXX_ATOMIC_NO_LINK_NEEDED )
set( _found FALSE )
if( CXX_ATOMIC_NO_LINK_NEEDED )
set( _found TRUE )
else()
check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
if (HAVE_LIBATOMIC)
set( OLD_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} )
list( APPEND CMAKE_REQUIRED_LIBRARIES "atomic" )
check_working_cxx_atomics( HAVE_CXX_ATOMICS_WITH_LIB )
set( CMAKE_REQUIRED_LIBRARIES ${OLD_CMAKE_REQUIRED_LIBRARIES} )
set( HAVE_CXX_ATOMICS_WITH_LIB TRUE )
set( _found TRUE )
endif()
endif()
add_library( std::atomic INTERFACE IMPORTED )
if( HAVE_CXX_ATOMICS_WITH_LIB )
set_property( TARGET std::atomic APPEND PROPERTY INTERFACE_LINK_LIBRARIES atomic )
endif()
set( Atomic_FOUND ${_found} CACHE BOOL "TRUE if we can run a program using std::atomic" FORCE )
if( Atomic_FIND_REQUIRED AND NOT Atomic_FOUND )
message( FATAL_ERROR "Cannot run simple program using std::atomic" )
endif()
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