Make buildextension for for macos with OpenMP

Author: giuliabaldini

README.md

@@ -19,16 +19,18 @@ Although the last two algorithms are not specifically designed for the k-Min-Sum
 
 ## Installation
 
-We **highly recommend** to install OpenMP. Parts of the code are parallelized and will be much faster. However, the code should run even without it. If that is not the case, open an issue!
+We **highly recommend** to install OpenMP. Parts of the code are parallelized and will be much faster. However, on Windows and MacOS the code also works without OpenMP. Nonetheless, the code was written for Linux and will achieve the best performance there.
 
 On Linux, you can use the following command:
 ```bash
 sudo apt-get install libomp-dev
 ```
+
 On MacOS, you can use the following command:
 ```bash
- brew install clang-omp
+ brew install llvm libomp
 ```
+However, it might be that MacOS does not find the installed library. In [`build_extension.py`](./build_extension.py), the paths are set manually. If it does not work for you, please clone the repository and run `poetry build`. You you see a message in red if your OpenMP is not found.
 
 Then, you can install the package via pip:
 ```bash

build_extension.py

@@ -1,7 +1,8 @@
 import os
+import platform
 import subprocess
 import warnings
-from typing import Any, Dict
+from typing import Any, Dict, List
 
 from setuptools import Extension
 from setuptools.command.build_ext import build_ext
@@ -25,7 +26,10 @@
 )
 
 
-def check_openmp_support() -> bool:
+def check_openmp_support() -> List[str]:
+    if platform.system() == "Windows":
+        return []
+
     openmp_test_code = """
     #include <omp.h>
     #include <stdio.h>
@@ -44,23 +48,33 @@ def check_openmp_support() -> bool:
         f.write(openmp_test_code)
 
     try:
+        if platform.system() == "Darwin":
+            cmd_params = [
+                "-Xclang",
+                "-fopenmp",
+                "-I/usr/local/opt/libomp/include",
+                "-L/usr/local/opt/libomp/lib",
+                "-lomp",
+            ]
+        else:
+            cmd_params = ["-fopenmp"]
         # Try to compile the code with OpenMP support
         result = subprocess.run(
-            ["gcc", "-fopenmp", "test_openmp.c", "-o", "test_openmp"],
+            ["gcc"] + cmd_params + ["test_openmp.c", "-o", "test_openmp"],
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
         )
         if result.returncode != 0:
-            return False
+            return []
 
         # Run the compiled program
         result = subprocess.run(
             ["./test_openmp"], stdout=subprocess.PIPE, stderr=subprocess.PIPE
         )
         if result.returncode == 0:
-            return True
+            return cmd_params
         else:
-            return False
+            return []
     finally:
         os.remove("test_openmp.c")
         if os.path.exists("test_openmp"):
@@ -71,24 +85,23 @@ class BuildExt(build_ext):
     """A custom build extension for adding -stdlib arguments for clang++."""
 
     def build_extensions(self) -> None:
-        if os.name == "nt":
-            support = True
-        else:
-            support = check_openmp_support()
+        openmp_params = check_openmp_support()
 
         # '-std=c++11' is added to `extra_compile_args` so the code can compile
         # with clang++. This works across compilers (ignored by MSVC).
         for extension in self.extensions:
             extension.extra_compile_args.append("-std=c++11")
-            if support:
-                extension.extra_compile_args.append("-fopenmp")
-                extension.extra_link_args.append("-lgomp")
-            else:
+            if len(openmp_params) == 0:
                 warnings.warn(
                     "\x1b[31;20m OpenMP is not installed on this system. "
                     "Please install it to have all the benefits from the program.\x1b[0m"
                 )
+            else:
+                for param in openmp_params:
+                    extension.extra_compile_args.append(param)
 
+                if platform.system() == "Linux":
+                    extension.extra_link_args.append("-lgomp")
         try:
             build_ext.build_extensions(self)
         except CompileError: