Trac #30351: Fix building html documentation on macOS

Building html documentation fails on macOS for Sage 9.2.beta8.

Initial report:

- [https://groups.google.com/d/msg/sage-release/spalYgXKr-4/gXp_2tsNBwAJ
sage-release, 2020-08-13]

URL: https://trac.sagemath.org/30351
Reported by: slelievre
Ticket author(s): Dima Pasechnik
Reviewer(s): John Palmieri

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
 

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

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()