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Note C API incompatibilities

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Andrew M. Kuchling 2006-04-12 12:27:50 +00:00
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Doc/whatsnew/whatsnew25.tex
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@ -1453,6 +1453,23 @@ actually drop when you delete them, and the memory may be returned to
the operating system. (Implemented by Evan Jones, and reworked by Tim the operating system. (Implemented by Evan Jones, and reworked by Tim
Peters.) Peters.)
Note that this change means extension modules need to be more careful
with how they allocate memory. Python's API has a number of different
functions for allocating memory that are grouped into families. For
example, \cfunction{PyMem_Malloc()}, \cfunction{PyMem_Realloc()}, and
\cfunction{PyMem_Free()} are one family that allocates raw memory,
while \cfunction{PyObject_Malloc()}, \cfunction{PyObject_Realloc()},
and \cfunction{PyObject_Free()} are another family that's supposed to
be used for creating Python objects.
Previously these different families all reduced to the platform's
\cfunction{malloc()} and \cfunction{free()} functions. This meant
it didn't matter if you got things wrong and allocated memory with the
\cfunction{PyMem} function but freed it with the \cfunction{PyObject}
function. With the obmalloc change, these families now do different
things, and mismatches will probably result in a segfault. You should
carefully test your C extension modules with Python 2.5.
\item Coverity, a company that markets a source code analysis tool \item Coverity, a company that markets a source code analysis tool
called Prevent, provided the results of their examination of the Python called Prevent, provided the results of their examination of the Python
source code. The analysis found a number of refcounting bugs, often source code. The analysis found a number of refcounting bugs, often
@ -1472,6 +1489,21 @@ changes to your code:
\item The \module{pickle} module no longer uses the deprecated \var{bin} parameter. \item The \module{pickle} module no longer uses the deprecated \var{bin} parameter.
\item C API: Many functions now use \ctype{Py_ssize_t}
instead of \ctype{int} to allow processing more data
on 64-bit machines. Extension code may need to make
the same change to avoid warnings and to support 64-bit machines.
See the earlier
section~ref{section-353} for a discussion of this change.
\item C API:
The obmalloc changes mean that
you must be careful to not mix usage
of the \cfunction{PyMem_*()} and \cfunction{PyObject_*()}
families of functions. Memory allocated with
one family's \cfunction{*_Malloc()} must be
freed with the corresponding family's \cfunction{*_Free()} function.
\end{itemize} \end{itemize}