From 488bba4768c034c741fa7e929168d354a5a86306 Mon Sep 17 00:00:00 2001
From: Dima Pasechnik <dima@pasechnik.info>
Date: Sun, 23 Aug 2020 19:41:17 +0100
Subject: [PATCH 1/2] on macOS set OMP_NUM_THREADS to 1 for docbuild and tests

---
 build/bin/sage-site   | 7 +++++++
 src/bin/sage-runtests | 9 ++++++---
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/build/bin/sage-site b/build/bin/sage-site
index 44d8e3acff9..ef5762d3cdc 100755
--- a/build/bin/sage-site
+++ b/build/bin/sage-site
@@ -157,6 +157,13 @@ if [ "$1" = "-docbuild" -o "$1" = "--docbuild" ]; then
     # cause the build to hang. If stdin is /dev/null, TeX just aborts.
     shift
     export LANG=C # to ensure it is possible to scrape out non-EN locale warnings
+
+    # See #30351: bugs in macOS implementations of openblas/libgopm can cause
+    # docbuild to hang if multiple OpenMP threads are allowed.
+    if [ `uname` = 'Darwin' ]; then
+        export OMP_NUM_THREADS=1
+    fi
+
     exec sage-python -m sage_setup.docbuild "$@" </dev/null
 fi
 
diff --git a/src/bin/sage-runtests b/src/bin/sage-runtests
index 32d3fddc778..be4e52f5701 100755
--- a/src/bin/sage-runtests
+++ b/src/bin/sage-runtests
@@ -168,10 +168,13 @@ if __name__ == "__main__":
                     # cause us to run out of physical memory, leading to system
                     # instability (as opposed to virtual memory allocs failing)
                     options.memlimit = -1
-
     # Limit the number of threads to 2 to save system resources.
-    # See Trac #23713 and #23892
-    os.environ["OMP_NUM_THREADS"] = "2"
+    # See Trac #23713, #23892, #30351
+    if sys.platform == 'darwin':  
+        os.environ["OMP_NUM_THREADS"] = "1"
+    else:
+        os.environ["OMP_NUM_THREADS"] = "2"
+
     os.environ["SAGE_NUM_THREADS"] = "2"
 
     from sage.doctest.control import DocTestController

From 4b11a706e1267b385099d8691b4468efd974f94d Mon Sep 17 00:00:00 2001
From: Dima Pasechnik <dima@pasechnik.info>
Date: Mon, 24 Aug 2020 10:57:33 +0100
Subject: [PATCH 2/2] use the correct import location, not six.*

---
 src/sage_setup/docbuild/utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/sage_setup/docbuild/utils.py b/src/sage_setup/docbuild/utils.py
index 272f7e2d0f3..9fce8e4edae 100644
--- a/src/sage_setup/docbuild/utils.py
+++ b/src/sage_setup/docbuild/utils.py
@@ -113,7 +113,7 @@ def build_many(target, args, processes=None):
         WorkerDiedException: worker for 4 died with non-zero exit code -9
     """
     from multiprocessing import Process, Queue, cpu_count
-    from six.moves.queue import Empty
+    from queue import Empty
 
     if processes is None:
         processes = cpu_count()