From: David Wells <drwells@email.unc.edu>
Date: Sat, 27 Aug 2022 17:07:52 +0000 (-0400)
Subject: Set another OMP environment variable.
X-Git-Tag: v9.5.0-rc1~1010^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0e5b95765ed04784321f6530aa6ba2dec4fa647f;p=dealii.git

Set another OMP environment variable.

Both of these environment variables control the number of threads - if we set
one we should set the other.

In my shell I always set OMP_THREAD_LIMIT=1 since I don't want to use OpenMP.
For whatever reason stopped working recently, resulting in OpenBLAS trying to
yield execution to nonexistent other threads since some functions expect one
thread to exist and others expect two.
---

diff --git a/cmake/scripts/run_test.sh b/cmake/scripts/run_test.sh
index bb016c67db..c347497997 100644
--- a/cmake/scripts/run_test.sh
+++ b/cmake/scripts/run_test.sh
@@ -58,8 +58,18 @@ case $STAGE in
       export TEST_N_THREADS
     fi
 
-    # Limit the OpenMP pool to two threads.
+    # Limit the OpenMP pool to two threads. Set both variables in case the
+    # caller has either one set.
+    #
+    # These variables do different things and are interpreted by, e.g., GOMP and
+    # openBLAS in slightly different ways so it is best to set both to avoid
+    # inconsistencies. For reference:
+    # 1. OMP_NUM_THREADS permits nesting, e.g., if we were using OpenMP we could
+    #    set it to 4,2,1 to set parallelization levels inside parallelized blocks
+    # 2. OMP_THREAD_LIMIT limits the total number of threads, independent of
+    #    nesting
     export OMP_NUM_THREADS="2"
+    export OMP_THREAD_LIMIT="2"
 
     # Allow oversubscription for MPI (needed for Openmpi@3.0)
     export OMPI_MCA_rmaps_base_oversubscribe=1