You can't modify the data during the kernel execution, if that's what you're trying to achieve.
The API wont even allow you do to it:
e.g. you can only write to a mapped buffer when it's mapped, and you can't pass a mapped buffer to enqueuendrangekernel.
Even with zero-copy buffers there are things like caches to flush and synchronise and so forth, mmu tables, etc.
Your example is invalid api use as you cannot access Pointer after calling unmap. unmap should be considered the same way free() is: once you've called it that pointer cannot be re-used.
So, you can transfer memory whilst another kenel is in process, but you cannot modify the memory that the executing one is using. And this is a good thing.
