On 2014-12-10 19:08, Matt wrote:
Sorry if this has been covered before, and also that I'm a complete noob, but
I'm thinking about trying a first project in Rust, and trying to learn enough
to get started.
My plan is for an on-disk key-value store. I'm going to end up writing arrays
of numbers to disk, and then needing to efficiently read them out of a mmap-ed
file. So I'm wondering how in Rust you efficiently/zero-copy-ly take some slice
of a read-only mmap and treat it as e.g. a vector of ints?
I see Vec.from_raw_parts() and Vec.from_raw_buf(), but I don't really
understand the difference between them, and also they seem like they just give
you a vector of the pointer's type, so I don't know how you use them convert
the u8s you get from MemoryMap.data() into a vector of a different type, e.g.
32 bit ints.
It seems like there should be a higher level API for this kind of thing, where
"casting" a slice of a read-only memory buffer into an immutable vector is not
an unsafe operation (I mean, you can do that in Python ;) Either I don't see it in the
docs, or it doesn't exist yet; just wondering which :)
Maybe this function will help you:
http://doc.rust-lang.org/std/os/struct.MemoryMap.html
At least on Linux you should be able to open a file, get its fd using
as_raw_fd() and pass that into the call to MemoryMap::new (see
MapOption::MapFd()).
// David
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