What if thread safety wasn't an issue?
-dave
On Dec 3, 2:41 pm, Kenton Varda <[EMAIL PROTECTED]> wrote:
> Ehhh... Reference counting is slow (assuming it needs to be thread-safe),
> and I think even adding it as an option would add an excessive amount of
> complication to the system.
>
> On Wed, Dec 3, 2008 at 2:04 PM, Dave Bailey <[EMAIL PROTECTED]> wrote:
>
> > On Dec 3, 2:00 pm, Dave Bailey <[EMAIL PROTECTED]> wrote:
> > > On Dec 2, 10:49 pm, Kenton Varda <[EMAIL PROTECTED]> wrote:
>
> > > > C++ compatibility matters because eventually we want to be able to
> > generate
> > > > Python code which just wraps C++ code for efficiency. C++ isn't
> > garbage
> > > > collected, so append() can't easily be implemented in this case without
> > > > having ownership problems. Slice assignment has the same problem.
> > > > Also note that even pure-python protocol buffers have a sort of
> > "ownership"
> > > > issue: Sub-messages all contain pointers back to their parents, so
> > that
> > > > when a sub-message is modified, the parent's cached size can be marked
> > > > dirty. (Also, singular sub-messages have to inform their parents when
> > the
> > > > first field within them is set, but that doesn't apply here.)
>
> > (Here is my post without all of the ridiculous formatting):
>
> > While you're on this topic, I ran into this ownership issue while
> > implementing the Perl/XS wrapper around the generated C++ code. I
> > think it is the same issue that would face the author of a Python or
> > Ruby C++ extension of the generated C++. I ended up having to new() a
> > copy of every message that I transferred from C++ to Perl or vice
> > versa. So, for example, a statement like
>
> > $team->member($i)->set_first_name('Dave');
>
> > won't have the same effect as (C++)
>
> > team.mutable_member(i)->set_first_name("Dave");
>
> > because $team->member($i) will generate a copy of the underlying C++
> > object, so that it can be managed by Perl's reference counting without
> > any concern as to whether or not the underlying C++ object has been
> > deleted because the containing message went out of scope.
>
> > Anyway, I thought it might be possible to allow for shared ownership
> > of a message object if there were a reference counted variant of
> > RepeatedPtrField<T> (something like RepeatedSharedPtrField<T> or
> > whatever), which would provide incref() and decref() methods such that
> > Perl and C++ could use the same underlying C++ objects in the
> > generated code. This would really help the performance of the Perl/XS
> > code if all of that copy construction could be avoided somehow. The C+
> > + code generator would need an option that would instruct it to
> > generate RepeatedSharedPtrField<T> members (and incref and decref
> > calls, where appropriate) for repeated messages (instead of using the
> > default RepeatedPtrField<T>).
>
> > What do you think? Is something like this possible, even though it
> > would require a change to protobuf? It is an issue for all {Python,
> > Perl, Ruby, ...}/C++ extension wrappers for Protocol Buffers. I have
> > found that protobuf is a faster Perl data serialization mechanism that
> > the (generic) Storable module, but I think it can be even faster.
>
> > -dave
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