[Python-3000] patch: bytes object PyBUF_LOCKDATA read-only and immutable support

[Gregory P. Smith]

I'm inclined to let this one wait for 3.0a2, I'm out of python time for the
week and will be out of town (but online) until next Thursday. Pairing up to
finish it later on would be nice if needed.  I'm happy if the immutable
support is dropped, I just figured I'd include it as an example once I
realized how easy it was.  I don't want hashable bytes objects either (let
someone implement that using a subclass in python :).

As for the _getbuffer() stuff I left it as a comment because I hadn't looked
into it in enough detail yet, you're right about the GIL.

-gps

On 8/29/07, Guido van Rossum <guido at python.org> wrote:
>
> That's a huge patch to land so close before a release. I'm not sure I
> like the immutability API -- it won't be useful unless we add a hash
> method, and then we have all sorts of difficulties again -- the
> distinction between a hashable and an unhashable object should be made
> by type, not by value (tuples containing unhashable values
> notwithstanding).
>
> I don't understand the comment about using PyBUF_WRITABLE in
> _getbuffer() -- this is only used for data we're *reading* and I don't
> think the GIL is even released while we're reading such things.
>
> If you think it's important to get this in the 3.0a1 release, we
> should pair-program on it ASAP, preferable tomorrow morning.
> Otherwise, let's do a review next week.
>
> --Guido
>
> On 8/29/07, Gregory P. Smith <greg at krypto.org> wrote:
> > Attached is what I've come up with so far.  Only a single field is
> > added to the PyBytesObject struct.  This adds support to the bytes
> > object for PyBUF_LOCKDATA buffer API operation.  bytes objects can be
> > marked temporarily read-only for use while the buffer api has handed
> > them off to something which may run without the GIL (think IO).  Any
> > attempt to modify them during that time will raise an exception as I
> > believe Martin suggested earlier.
> >
> > As an added bonus because its been discussed here, support for setting
> > a bytes object immutable has been added since its pretty trivial once
> > the read only export support was in place.  Thats not required but was
> > trivial to include.
> >
> > I'd appreciate any feedback.
> >
> > My TODO list for this patch:
> >
> >  0. Get feedback and make adjustments as necessary.
> >
> >  1. Deciding between PyBUF_SIMPLE and PyBUF_WRITEABLE for the internal
> >     uses of the _getbuffer() function.  bytesobject.c contains both
> readonly
> >     and read-write uses of the buffers, i'll add boolean parameter for
> >     that.
> >
> >  2. More testing: a few tests in the test suite fail after this but the
> >     number was low and I haven't had time to look at why or what the
> >     failures were.
> >
> >  3. Exporting methods suggested in the TODO at the top of the file.
> >
> >  4. Unit tests for all of the functionality this adds.
> >
> > NOTE: after these changes I had to make clean and rm -rf build before
> > things would not segfault on import.  I suspect some things (modules?)
> > were not properly recompiled after the bytesobject.h struct change
> > otherwise.
> >
> > -gps
> >
> >
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> >
> >
>
>
> --
> --Guido van Rossum (home page: http://www.python.org/~guido/)
>
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