disable openmp (GNU openmp not fork safe; causing hangs)

recipe/build.sh

@@ -20,7 +20,9 @@ if [[ ${target_platform} == osx-64 ]]; then
     export LAPACK_FFLAGS="$LAPACK_FFLAGS -Wl,-rpath,$PREFIX/lib"
     export FFLAGS="$FFLAGS -Wl,-rpath,$PREFIX/lib"
 else
-    USE_OPENMP="1"
+    # Gnu OpenMP is not fork-safe.  We disable openmp right now, so that downstream packages don't hang as a result of this.
+    # USE_OPENMP="1"
+    USE_OPENMP="0"
 fi
 
 # Build all CPU targets and allow dynamic configuration
@@ -29,8 +31,14 @@ fi
 # setting OPENBLAS_NUM_THREADS before loading the library.
 # Because -Wno-missing-include-dirs does not work with gfortran:
 [[ -d "${PREFIX}"/include ]] || mkdir "${PREFIX}"/include
+
+# USE_SIMPLE_THREADED_LEVEL3 is necessary to avoid hangs when more than one process uses blas:
+#    https://github.com/xianyi/OpenBLAS/issues/1456
+#    https://github.com/xianyi/OpenBLAS/issues/294
+#    https://github.com/scikit-learn/scikit-learn/issues/636
+
 make DYNAMIC_ARCH=1 BINARY=${ARCH} NO_LAPACK=0 NO_AFFINITY=1 USE_THREAD=1 NUM_THREADS=128 \
-     USE_OPENMP="${USE_OPENMP}" CFLAGS="${CF}" FFLAGS="${FFLAGS}"
+     USE_OPENMP="${USE_OPENMP}" USE_SIMPLE_THREADED_LEVEL3=1 CFLAGS="${CF}" FFLAGS="${FFLAGS}"
 OPENBLAS_NUM_THREADS=${CPU_COUNT} CFLAGS="${CF}" FFLAGS="${FFLAGS}" make test
 OPENBLAS_NUM_THREADS=${CPU_COUNT} CFLAGS="${CF}" FFLAGS="${FFLAGS}" make lapack-test
 CFLAGS="${CF}" FFLAGS="${FFLAGS}" make install PREFIX="${PREFIX}"

recipe/meta.yaml

@@ -18,7 +18,7 @@ source:
     - 0003-turn-TLS-off.patch
 
 build:
-  number: 2
+  number: 3
   skip: true  # [win and vc<14]
 
 requirements: