Re: [Openexr-devel] Patch-compatibilty with versioned namespaces

[Peter Hillman]

Hi Ollie!

> Am I right in saying that, without versioned namespaces, patches are always 
> binary compatible and minor versions always incompatible?
Yes, this should be the case
> Is there a patch-compatible namespacing method already provided (and if so, 
> what is it)?

The existing method is patch-compatible: patches will still be released 
with the _2_0_0 namespace. We will only move from on from _2_0_0 and 
.so.20 if binary compatibility has to be broken.
So, v2.0.X releases would all use the _2_0_0 namespace for all classes.

If binary compatibility needs to be broken, we will most likely update 
the effected libraries to namespace _2_1_0, at which time the .so 
version number will be bumped up to .so.21. This way, a large 
application can safely load both old and new libraries. Indeed, this 
ability is one of the reasons for switching to this versioned namespace 
scheme.


> What's the soname version number based on?
The soname version number (probably) tracks the first two digits of the 
namespace version number.

(the last digit in the namespace version is somewhat misleading, as it 
doesn't imply patch level: it's there only for an edge case of providing 
multiple versions of an object within the same .so but in different 
namespaces, which we're really hoping we don't need to do in official 
releases, but for internal builds might be the easiest way out of a hole)

At least, that's my understanding of the plan!

Peter

On 09/01/13 03:10, Ollie Harding wrote:
> Hi,
>
> I wonder if somebody could clarify some versioning info for me, or point me at 
> the bits of the docs which I've skimmed over too quickly?
>
> I'm building v2.0.0 using the --enable-namespaceversioning flag for 
> ./configure, which gives me e.g.
>
>      Imath_2_0_0::SingMatrixExc::~SingMatrixExc()
>
> This will of course mean that I cannot drop in a future v2.0.1 library since 
> the Imath_2_0_0 symbols will no longer exist, although the library will 
> presumably still share the .so.20 soname. I suspect I'm using the wrong method 
> of making a unique namespace, as I in fact want a namespace which retains patch 
> compatibility, e.g. maybe Imath_2_0.
>
> So my questions are:
>
>      * Am I right in saying that, without versioned namespaces, patches are 
> always binary compatible and minor versions always incompatible?
>      * Is there a patch-compatible namespacing method already provided (and if 
> so, what is it)?
>      * What's the soname version number based on?
>
> Many thanks,
>
> Ollie
>
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