On Tue, May 21, 2019, 8:43 AM Antoine Pitrou <anto...@python.org> wrote:
> > Le 21/05/2019 à 13:42, Wes McKinney a écrit : > > hi Antoine, > > > > On Tue, May 21, 2019 at 5:48 AM Antoine Pitrou <anto...@python.org> > wrote: > >> > >> > >> Hi Wes, > >> > >> How does copy-on-write play together with memory-mapped data? It seems > >> that, depending on whether the memory map has several concurrent users > >> (a condition which may be timing-dependent), we will either persist > >> changes on disk or make them ephemeral in memory. That doesn't sound > >> very user-friendly, IMHO. > > > > With memory-mapping, any Buffer is sliced from the parent MemoryMap > > [1] so mutating the data on disk using this interface wouldn't be > > possible with the way that I've framed it. > > Hmm... I always forget that SliceBuffer returns a read-only view. > The more important issue is that parent_ is non-null. The idea is that no mutation is allowed if we reason that another Buffer object has access to the address space of interest. I think this style of copy-on-write is a reasonable compromise that prevents most kinds of defensive copying. > Regards > > Antoine. >
