Update MemoryManagement.md

Author: Roberto De Ioris

docs/MemoryManagement.md

@@ -45,3 +45,34 @@ Traceback (most recent call last):
   File "<string>", line XX, in <module>
 Exception: PyUObject is in invalid state
 ```
+
+Very long scripts, that do lot of stuff, often triggering UE4 GC, could be blocked in the middle of their execution by this kind of errors. In such a case (like you would do in C++) you need to inform the UE GC on how to deal with them (for avoiding their destruction).
+
+Pay attention, as once you tell the UE GC to not destroy a UObject, that UObject (and its python mapping) will stay in memory (so you will end with a leak)
+
+## Strategy 1: Setting UObject flags to govern the GC
+
+When you create a UObject (from the C++ side, via the NewObject<T> api call) you can specify a bitmask of flags. By default the python api only use the RF_Public flag:
+  
+https://api.unrealengine.com/INT/API/Runtime/CoreUObject/UObject/EObjectFlags/index.html
+
+You can change this bitmask with the set_obj_flags() python function:
+
+```python
+import unreal_engine as ue
+
+from unreal_engine.classes import BlueprintFactory
+
+factory = BlueprintFactory()
+# assign mask 0x00000001|0x00000002
+factory.set_obj_flags(ue.RF_PUBLIC|ue.RF_STANDALONE)
+# run GC
+ue.console_exec('obj gc')
+# this will normally print the UObject repr
+print(factory)
+```
+
+The RF_Standalone flag (RF_STANDALONE in python api) will marks a UObject as 'standalone' so it will remain resident in memory forever.
+This is a pretty raw approach (unless you are sure that you need a resident object). For having more control the second strategy will be way more better...
+
+## Strategy 2: The Root Set