Detect, contain, and warn about the OpenMP issue of having multiple O…

…penMP runtimes that occurs in conda environments containing numpy and pip-installed galpy

galpy/util/_load_extension_libs.py

@@ -1,5 +1,7 @@
 # _load_extension_libs.py: centralized place to load the C extensions
 import ctypes
+import re
+import subprocess
 import sys
 import sysconfig
 import warnings
@@ -19,12 +21,55 @@
 _libgalpy_actionAngleTorus = None
 _libgalpy_actionAngleTorus_loaded = None
 
+_checked_openmp_issue = False
 
-def load_libgalpy():
+
+def _detect_openmp_issue():
+    # Check whether we get an error of the type "OMP: Error #15: Initializing libomp.dylib, but found libomp.dylib already initialized.", which occurs, e.g., when using pip-installed galpy with conda-installed numpy and causes segmentation faults and general issues
+    # This is a known issue with OpenMP and is not galpy's fault (GitHub Copilot suggested this comment!)
+
+    # Check this by running a subprocess that tries to import the C library without this check
+    try:
+        subprocess.run(
+            [
+                sys.executable,
+                "-c",
+                "from galpy.util._load_extension_libs import load_libgalpy; load_libgalpy(check_openmp_issue=False)",
+            ],
+            check=True,
+            capture_output=True,
+        )
+    except subprocess.CalledProcessError as e:  # pragma: no cover
+        if re.match(
+            r"OMP: Error #15: Initializing libomp[0-9]*.dylib, but found libomp[0-9]*.dylib already initialized",
+            e.stderr.decode("utf-8"),
+        ):
+            warnings.warn(
+                "Encountered OpenMP issue with multiple OpenMP runtimes causing conflicts and segmentation faults (similar to https://github.com/pytorch/pytorch/issues/78490). "
+                "This generally happens when you combine a pip-installed galpy with a conda-installed numpy. "
+                "If you are using conda, your best bet is to install galpy with conda-forge, because there is little advantage to using pip. "
+                "If you insist on using pip, you can try installing galpy with the --no-binary galpy flag, but note that you have to have the GSL and OpenMP installed and available for linking (e.g., using 'brew install gsl libomp' on a Mac, but make sure to add the OpenMP library to your CFLAGS/LDFLAGS/LD_LIBRARY_PATH as it is keg-only; please refer to galpy's installation page for more info). "
+                "Please open an Issue or Discussion on the galpy GitHub repository if you require further assistance.\n"
+                "For now, we will disable the libgalpy C extension module to avoid segmentation faults and other issues, but be aware that this significantly slows down the code.",
+                galpyWarning,
+            )
+            return True
+    else:
+        return False
+    finally:
+        global _checked_openmp_issue
+        _checked_openmp_issue = True
+
+
+def load_libgalpy(check_openmp_issue=True):
     global _libgalpy
     global _libgalpy_loaded
     if _libgalpy_loaded is False or not _libgalpy is None:
         return (_libgalpy, _libgalpy_loaded)
+    if check_openmp_issue and not _checked_openmp_issue:
+        if _detect_openmp_issue():  # pragma: no cover
+            _libgalpy_loaded = False
+            return (_libgalpy, _libgalpy_loaded)
     outerr = None
     # Add top-level galpy repository directory for pip install (-e) .,
     # just becomes site-packages for regular install