Unmap of NumPy memmap
Yes, it's only closed when the object is garbage-collected; memmap.close method does nothing.
You can call x._mmap.close(), but keep in mind that any further access to the x object will crash python.
I can't find any documentation on how numpy handles unmapping of previously memory mapped regions: munmap for numpy.memmap() and numpy.load(mmap_mode).
My guess is it's done only at garbage collection time, is that correct?