MAINT: Fix OpenMP runtime error on mac (#13294)

jeremiedbb · glemaitre · commit ffd27c8594fa · 2019-02-27T17:25:46.000+01:00
diff --git a/build_tools/azure/install.sh b/build_tools/azure/install.sh
@@ -16,9 +16,6 @@ if [[ "$UNAMESTR" == "Darwin" ]]; then
     export CXXFLAGS="$CXXFLAGS -I/usr/local/opt/libomp/include"
     export LDFLAGS="$LDFLAGS -L/usr/local/opt/libomp/lib -lomp"
     export DYLD_LIBRARY_PATH=/usr/local/opt/libomp/lib
-
-    # avoid error due to multiple OpenMP libraries loaded simultaneously
-    export KMP_DUPLICATE_LIB_OK=TRUE
 fi
 
 make_conda() {
diff --git a/build_tools/travis/install.sh b/build_tools/travis/install.sh
@@ -38,9 +38,6 @@ then
     export CXXFLAGS="$CXXFLAGS -I/usr/local/opt/libomp/include"
     export LDFLAGS="$LDFLAGS -L/usr/local/opt/libomp/lib -lomp"
     export DYLD_LIBRARY_PATH=/usr/local/opt/libomp/lib
-
-    # avoid error due to multiple OpenMP libraries loaded simultaneously
-    export KMP_DUPLICATE_LIB_OK=TRUE
 fi
 
 make_conda() {
diff --git a/sklearn/__init__.py b/sklearn/__init__.py
@@ -16,6 +16,7 @@
 import re
 import warnings
 import logging
+import os
 
 from ._config import get_config, set_config, config_context
 
@@ -47,6 +48,17 @@
 __version__ = '0.21.dev0'
 
 
+# On OSX, we can get a runtime error due to multiple OpenMP libraries loaded
+# simultaneously. This can happen for instance when calling BLAS inside a
+# prange. Setting the following environment variable allows multiple OpenMP
+# libraries to be loaded. It should not degrade performances since we manually
+# take care of potential over-subcription performance issues, in sections of
+# the code where nested OpenMP loops can happen, by dynamically reconfiguring
+# the inner OpenMP runtime to temporarily disable it while under the scope of
+# the outer OpenMP parallel section.
+os.environ.setdefault("KMP_DUPLICATE_LIB_OK", "True")
+
+
 try:
     # This variable is injected in the __builtins__ by the build
     # process. It is used to enable importing subpackages of sklearn when
