fix: avoid using openmp for pyodide

Author: gangula-karthik

meson.build

@@ -106,4 +106,5 @@ endif
 # Needed by pandas.test() when it looks for the pytest ini options
 py.install_sources('pyproject.toml', subdir: 'pandas')
 
+# Pass build flags to subdirectories
 subdir('pandas')

pandas/_libs/algos.pyx

@@ -398,6 +398,7 @@ def nancorr(
                 ssqds[j] = ssqd
 
     if use_parallel:
+        # Use parallel execution with prange (only works if OpenMP is available)
         for xi in prange(K, schedule="dynamic", nogil=True):
             for yi in range(xi + 1):
                 covxy = 0
@@ -446,6 +447,7 @@ def nancorr(
                     else:
                         result[xi, yi] = result[yi, xi] = NaN
     else:
+        # Use sequential execution with regular range
         with nogil:
             for xi in range(K):
                 for yi in range(xi + 1):

pandas/_libs/meson.build

@@ -1,15 +1,3 @@
-# Add OpenMP dependency detection at the top of the file
-openmp_dep = dependency('openmp', required: false)
-if not openmp_dep.found()
-    cc = meson.get_compiler('c')
-    if cc.has_argument('-fopenmp')
-        openmp_dep = declare_dependency(
-            compile_args: ['-fopenmp'],
-            link_args: ['-fopenmp'],
-        )
-    endif
-endif
-
 _algos_take_helper = custom_target(
     'algos_take_helper_pxi',
     output: 'algos_take_helper.pxi',
@@ -62,6 +50,15 @@ _khash_primitive_helper_dep = declare_dependency(
     sources: _khash_primitive_helper,
 )
 
+# Use the parent's WebAssembly detection and OpenMP configuration
+# (is_pyodide_build and openmp_dep are inherited from parent meson.build)
+
+# Conditional dependencies for algos module
+algos_deps = [_khash_primitive_helper_dep]
+if openmp_dep.found() and not is_pyodide_build
+    algos_deps += [openmp_dep]
+endif
+
 cdata = configuration_data()
 if cy.version().version_compare('>=3.1.0')
     cdata.set('freethreading_compatible', '1')
@@ -82,7 +79,7 @@ libs_sources = {
     # numpy include dir is implicitly included
     'algos': {
         'sources': ['algos.pyx', _algos_common_helper, _algos_take_helper],
-        'deps': [_khash_primitive_helper_dep, openmp_dep],
+        'deps': algos_deps,
     },
     'arrays': {'sources': ['arrays.pyx']},
     'groupby': {'sources': ['groupby.pyx']},

setup.py

@@ -28,6 +28,16 @@
 cmdclass = versioneer.get_cmdclass()
 
 
+# Check for WebAssembly/Emscripten build environment
+def is_platform_emscripten():
+    """Check if we're building for WebAssembly/Emscripten (Pyodide)."""
+    return (
+        sys.platform == "emscripten"
+        or os.environ.get("EMSCRIPTEN", "").lower() in ("1", "true", "yes")
+        or os.environ.get("PYODIDE", "").lower() in ("1", "true", "yes")
+    )
+
+
 def is_platform_windows():
     return sys.platform in ("win32", "cygwin")
 
@@ -439,9 +449,17 @@ def srcpath(name=None, suffix=".pyx", subdir="src"):
         "pyxfile": "_libs/algos",
         "depends": _pxi_dep["algos"],
         "extra_compile_args": extra_compile_args
-        + (["-fopenmp"] if not is_platform_windows() else ["/openmp"]),
+        + (
+            (["-fopenmp"] if not is_platform_windows() else ["/openmp"])
+            if not is_platform_emscripten()
+            else []
+        ),
         "extra_link_args": extra_link_args
-        + (["-fopenmp"] if not is_platform_windows() else []),
+        + (
+            (["-fopenmp"] if not is_platform_windows() else [])
+            if not is_platform_emscripten()
+            else []
+        ),
     },
     "_libs.arrays": {"pyxfile": "_libs/arrays"},
     "_libs.groupby": {"pyxfile": "_libs/groupby"},