Use llvm-openmp package for conda builds to avoid conflicts

- Other packages (e.g., numba 0.62+, openblas) may require llvm-openmp and
bundling our own creates conflicst.

Author: ggeorgakoudis

buildscripts/conda-recipes/pyomp/meta.yaml

@@ -19,6 +19,7 @@ build:
     - export CXX=${PREFIX}/bin/clang++
     - export VERBOSE=1
     - export CPPFLAGS="-mmacosx-version-min=${MACOSX_DEPLOYMENT_TARGET} -isystem ${PREFIX}/include -D_FORTIFY_SOURCE=2" # [osx]
+    - export DISABLE_BUNDLED_LIBOMP=1
     - rm -rf build dist src/*.egg-info
     - {{ PYTHON }} -m pip install -v .
 
@@ -48,19 +49,23 @@ requirements:
     - clang-tools {{ LLVM_VERSION }}
     - llvmdev {{ LLVM_VERSION }}
     - zlib
+    # require llvm-openmp for the openmp cpu runtime.
+    - llvm-openmp
     - elfutils # [linux]
     - libffi # [linux]
   run:
     - python
     - setuptools
     - numba >=0.62, <0.64
+    # require llvm-openmp for the openmp cpu runtime.
+    - llvm-openmp
     - lark
     - cffi
 
 test:
   commands:
-    - test -f $SP_DIR/numba/openmp/libs/libomp/lib/libomp.dylib                        # [osx]
-    - test -f $SP_DIR/numba/openmp/libs/libomp/lib/libomp.so                           # [linux]
+    - test -f $SP_DIR/numba/openmp/libs/pass/libIntrinsicsOpenMP.dylib                 # [osx]
+    - test -f $SP_DIR/numba/openmp/libs/pass/libIntrinsicsOpenMP.so                    # [linux]
     - test -f $SP_DIR/numba/openmp/libs/libomp/lib/libomptarget-amdgpu.bc              # [linux]
     - test -f $SP_DIR/numba/openmp/libs/libomp/lib/libomptarget-nvptx.bc               # [linux]
     - test -f $SP_DIR/numba/openmp/libs/libomp/lib/libomptarget.so                     # [linux]

setup.py

@@ -205,9 +205,20 @@ def _prepare_source_openmp(sha256=None):
     return f"{sourcedir}/runtimes"
 
 
-setup(
-    ext_modules=[
-        CMakeExtension("pass", sourcedir="src/numba/openmp/libs/pass"),
+# Optionally disable bundled libomp build via DISABLE_BUNDLED_LIBOMP=1.  Used on
+# conda builds to avoid duplicate OpenMP runtime conflicts (e.g., numba 0.62+
+# and libopenblas already require llvm-openmp).
+def _should_bundle_libomp():
+    """Check if we should build and bundle the libomp runtime."""
+    disable = os.environ.get("DISABLE_BUNDLED_LIBOMP", "0")
+    return disable.lower() not in ("1", "true", "yes")
+
+
+# Build extensions: always include 'pass', conditionally include 'openmp'
+ext_modules = [CMakeExtension("pass", sourcedir="src/numba/openmp/libs/pass")]
+
+if _should_bundle_libomp():
+    ext_modules.append(
         CMakeExtension(
             "libomp",
             sourcedir=_prepare_source_openmp(),
@@ -219,8 +230,11 @@ def _prepare_source_openmp(sha256=None):
                 # under /usr/include and its gcc-toolset provided header files.
                 "-DCMAKE_NO_SYSTEM_FROM_IMPORTED=ON",
             ],
-        ),
-    ],
+        )
+    )
+
+setup(
+    ext_modules=ext_modules,
     cmdclass={
         "clean": CleanCommand,
         "build_ext": BuildCMakeExt,

src/numba/openmp/__init__.py

@@ -60,25 +60,45 @@
 
 def _init():
     sys_platform = sys.platform
+    from ctypes.util import find_library
 
     omplib = (
         libpath
         / "libomp"
         / "lib"
         / f"libomp{'.dylib' if sys_platform == 'darwin' else '.so'}"
     )
-    if DEBUG_OPENMP >= 1:
-        print("Found OpenMP runtime library at", omplib)
-    ll.load_library_permanently(str(omplib))
+
+    # Prefer bundled libomp if it exists.
+    if omplib.exists():
+        if DEBUG_OPENMP >= 1:
+            print("Found bundled OpenMP runtime library at", omplib)
+        ll.load_library_permanently(str(omplib))
+    else:
+        # There is no bundled libomp, try to find it in standard library paths.
+        system_omplib = find_library("omp")
+        if system_omplib:
+            if DEBUG_OPENMP >= 1:
+                print(f"Found system OpenMP runtime library: {system_omplib}")
+            ll.load_library_permanently(system_omplib)
+        else:
+            raise RuntimeError(
+                f"OpenMP runtime not found. Bundled library missing at {omplib} "
+                "and no system libomp found via ctypes.util.find_library('omp'). "
+                "Ensure libomp is available in library paths."
+            )
 
     # libomptarget is unavailable on apple, windows, so return.
     if sys_platform.startswith("darwin") or sys_platform.startswith("win32"):
         return
 
     omptargetlib = libpath / "libomp" / "lib" / "libomptarget.so"
-    if DEBUG_OPENMP >= 1:
-        print("Found OpenMP target runtime library at", omptargetlib)
-    ll.load_library_permanently(str(omptargetlib))
+    if omptargetlib.exists():
+        if DEBUG_OPENMP >= 1:
+            print("Found OpenMP target runtime library at", omptargetlib)
+        ll.load_library_permanently(str(omptargetlib))
+    elif DEBUG_OPENMP >= 1:
+        print(f"OpenMP target runtime not found at {omptargetlib}")
 
 
 _init()