Question

Suppose you’re calling a Win32 function that will fill in your byte array. You create an array of size 32, empty. Then pass it in to the Win32 function to be filled int, and use it later in your managed code. Does there exist the chance that the byte array might be moved or overwritten in between the time it was allocated and it is filled in by the Win32 function?

Answer 1

Short Answer: No, pinning is not necessary in this case

Longer Answer:

The CLR will automatically pin references to managed objects when they cross the PInvoke boundary. As soon as the PInvoke function exits the reference will be unpinned. So in situations like having a native function fill a byte[] no manually pinning is necessary because the object is only used by native code during the function call.

Manually pinning of the array becomes necessary if the native code caches the managed pointer. When this happens you must manually pin the array until the native code no longer needs the pointer. In this case I presume the pointer is not cached hence it’s not necessary to pin

Reference – http://msdn.microsoft.com/en-us/magazine/cc163910.aspx#S2