[IFC] force single-threading to avoid crashes

added test case for multi thread problem

src/Aardvark.Data.Ifc/IFCParser.cs

@@ -32,6 +32,7 @@ public static IFCData PreprocessIFC(string filePath, XbimEditorCredentials edito
             if (model.GeometryStore.IsEmpty)
             {
                 var context = new Xbim3DModelContext(model);
+                context.MaxThreads = 1;
                 //upgrade to new geometry representation, uses the default 3D model
                 context.CreateContext(null, true, false);    // THIS IS COSTLY!
             }

src/Tests/IfcTests/IfcTests.cs

@@ -66,5 +66,19 @@ public static void LoadSlab()
                 Assert.AreEqual(2, parsed.Materials.Count);
             });
         }
+
+        [Test]
+        public static void MultiThreadKiller()
+        {
+            // NOTE: In IFCParser -> change MaxThreads!
+            //  var context = new Xbim3DModelContext(model);
+            //  context.MaxThreads = 1; <- SINGLE-Thread works!
+            //  context.CreateContext(null, true, false);
+
+            LoadEmbeddedData(@"data\simple_scene.ifc", (filePath) => {
+                var parsed = IFCParser.PreprocessIFC(filePath);
+                Assert.AreEqual(5, parsed.Materials.Count);
+            });
+        }
     }
 }

src/Tests/IfcTests/IfcTests.csproj

@@ -17,6 +17,7 @@
   <ItemGroup>
     <EmbeddedResource Include="data\slab.ifc" />
     <EmbeddedResource Include="data\surface-model.ifc" />
+    <EmbeddedResource Include="data\simple_scene.ifc" />
     <EmbeddedResource Include="data\wall.ifc" />
   </ItemGroup>
   <Import Project="..\..\..\.paket\Paket.Restore.targets" />