Switch to single threaded default, resolving possible race condition

Author: hughcars

src/solidmodels/render.jl

@@ -924,7 +924,8 @@ function render!(
 
     # With the setting below, Gmsh will look for OMP_NUM_THREADS environment variables;
     # this needs to be >1 for HXT algorithm to use parallelism.
-    set_gmsh_option("General.NumThreads", gmsh_options, 0)
+    # Default to no threads, as there appear to be race conditions within gmsh.
+    set_gmsh_option("General.NumThreads", gmsh_options, 1)
 
     # Always save meshes in binary for faster disk I/O
     set_gmsh_option("Mesh.Binary", gmsh_options, 1)