Update README.md

henon · web-flow · commit 6c35195995d1 · 2019-06-08T11:03:32.000+02:00
diff --git a/README.md b/README.md
@@ -57,6 +57,27 @@ var result = np.cos(m);
 // get the floating point data of the result NDarray back to C#
 var data = result.GetData<double>(); // double[] { 0.54030231, -0.41614684, -0.9899925 , -0.65364362 }
 ```
+## Multi-threading considerations
+Python/NumPy doesn't have real multi-threading support. There is no advantage to calling `numpy` functions from different threads because `pythonnet` requires you to use the Global Interpreter Lock (GIL) when doing so: 
+
+```csharp
+var a = np.arange(1000);
+var b = np.arange(1000);
+Task.Run(()=> {
+  // when running on different threads you must lock!
+  using (Py.GIL())
+  {
+    np.matmul(a, b);
+  }
+});
+Task.Run(()=> {
+  // when running on different threads at the same time you must lock or you will get an exception!
+  using (Py.GIL())
+  {
+    np.matmul(a, b);
+  }
+});
+```
 
 ## Numpy.NET vs NumSharp
 
