[jira] [Commented] (DISPATCH-2270) Do not rely on long type being large enough to transfer C pointer values from C to Python

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DISPATCH-2270?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17446881#comment-17446881 ] 

ASF GitHub Bot commented on DISPATCH-2270:
------------------------------------------

jiridanek commented on pull request #1409:
URL: https://github.com/apache/qpid-dispatch/pull/1409#issuecomment-974717940


   This is IMO useful on all platforms, so it can be merged even if Windows is to remain unsupported.


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> Do not rely on long type being large enough to transfer C pointer values from C to Python
> -----------------------------------------------------------------------------------------
>
>                 Key: DISPATCH-2270
>                 URL: https://issues.apache.org/jira/browse/DISPATCH-2270
>             Project: Qpid Dispatch
>          Issue Type: Sub-task
>    Affects Versions: 1.17.0
>            Reporter: Jiri Daněk
>            Priority: Major
>
> {code}
> // We pass pointers as longs via the python interface, make sure this is safe.
> STATIC_ASSERT(sizeof(long) >= sizeof(void*), pointer_is_bigger_than_long);
> {code}
> This is wrong on Win64, where long is 4 bytes. There is multiple possible solutions:
> # use {{long long}}, trivial workaround
> ** https://docs.python.org/3/c-api/arg.html#c.Py_BuildValue
> # construct the python value explicitly, probably the nicest solution, and should not even add extra overhead
> ** https://docs.python.org/3/c-api/long.html#c.PyLong_FromVoidPtr
> # use PyCapsules, not a good fit for existing code, requires changing signature in C on the callee side
> ** https://docs.python.org/3/c-api/capsule.html
> ** https://docs.python.org/3/extending/extending.html?highlight=capsule#providing-a-c-api-for-an-extension-module
> and maybe even more possibilities. I am inclined to go with the PyLong_FromVoidPtr value constructor.



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