fails to link external OpenMP library

[hmoffatt]

On macOS, the clang/LLVM compiler does not include OpenMP support but it is available as an external library via brew:

brew install libomp

When this library is installed, it is correctly detected by the cmake scripts, but then the compile fails because src/CMakeLists.txt fails to include the include directory and fails to link the library.

I was able to get this to work by adding

if ( HAVE_OPENMP )
  include_directories ( ${OpenMP_C_INCLUDE_DIR} )
endif ( HAVE_OPENMP )

and to target_link_libraries

    ${OpenMP_libomp_LIBRARY}

This last one doesn't look 100% correct although it does work; the cmake script has not calculated a nice linker flag (-lomp).

[derselbst]

This last one doesn't look 100% correct although it does work; the cmake script has not calculated a nice linker flag (-lomp).

Could you please uncomment those two lines and try again?

fluidsynth/CMakeLists.txt

Lines 709 to 710 in 15bd824

	# set ( CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${OpenMP_EXE_LINKER_FLAGS}" )
	# set ( LIBFLUID_LIBS "${OpenMP_C_LIBRARIES};${LIBFLUID_LIBS}" )

[derselbst]

Also, which version of clang are you using? Because I tried to reproduce this in our Mac CI Build, but it keeps reporting that only openMP 201107 is supported, which in insufficient. No matter if libomp is installed or not.

[hmoffatt]

Uncommenting those lines fixes the linking, but it doesn't find the include file (/usr/local/include/omp.h) without also adding ${OpenMP_C_INCLUDE_DIR} to the include directories.

My clang is 12.0.5 as provided by Xcode 12.5 (currently the latest):

$ clang --version
Apple clang version 12.0.5 (clang-1205.0.22.9)
Target: x86_64-apple-darwin20.5.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

The parallel sound font loading does work nicely on macOS with these changes.

[hmoffatt]

By the way, the latest MSVC does support OpenMP 4.0 for 64-bit Windows applications. I haven't tested it yet as 32-bit support (which I need) is coming later.

[derselbst]

A PR is ready for this, feel free to test. Unfortunately, Mac11 is still not publicly available for Github Actions and AzureDevOps (actions/runner-images#2486), so I cannot see whether it actually works.

[hmoffatt]

That's working perfectly for me. Thanks.