Merge pull request #4194 from larsmans/openblas-docs

juliantaylor · juliantaylor · commit a724c93d071d · 2014-01-14T11:35:11.000-08:00
DOC: site.cfg: warn against OpenBLAS and multiprocessing
diff --git a/site.cfg.example b/site.cfg.example
@@ -83,6 +83,17 @@
 # for your configuration (in the following example we installed OpenBLAS with
 # ``make install PREFIX=/opt/OpenBLAS``.
 #
+# **Warning**: OpenBLAS, by default, is built in multithreaded mode. Due to the
+# way Python's multiprocessing is implemented, a multithreaded OpenBLAS can
+# cause programs using both to hang as soon as a worker process is forked on
+# POSIX systems (Linux, Mac). Python 3.4 will introduce a new feature in
+# multiprocessing, called the "forkserver", which solves this problem. For
+# older versions, either compile OpenBLAS with multithreading turned off or
+# use Python threads instead of multiprocessing.
+# (This problem does not exist with multithreaded ATLAS.)
+#
+# http://docs.python.org/3.4/library/multiprocessing.html#contexts-and-start-methods
+#
 # [openblas]
 # libraries = openblas
 # library_dirs = /opt/OpenBLAS/lib
