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Tweak the description of pymalloc. Mention pymemcompat.h.

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Michael W. Hudson 2002-06-10 13:19:42 +00:00
parent b3bfa7f9dc
commit 497bdd69f2
1 changed files with 32 additions and 22 deletions
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54
Doc/whatsnew/whatsnew23.tex
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@ -357,9 +357,10 @@ or warnings.filterwarnings().
An experimental feature added to Python 2.1 was a specialized object
allocator called pymalloc, written by Vladimir Marangozov. Pymalloc
was intended to be faster than the system \function{malloc()} and have
less memory overhead. The allocator uses C's \function{malloc()}
function to get large pools of memory, and then fulfills smaller
memory requests from these pools.
less memory overhead for typical allocation patterns of Python
programs. The allocator uses C's \function{malloc()} function to get
large pools of memory, and then fulfills smaller memory requests from
these pools.
In 2.1 and 2.2, pymalloc was an experimental feature and wasn't
enabled by default; you had to explicitly turn it on by providing the
@ -378,32 +379,34 @@ and \function{free()}, meaning that if you accidentally called
mismatched functions, the error wouldn't be noticeable. When the
object allocator is enabled, these functions aren't aliases of
\function{malloc()} and \function{free()} any more, and calling the
wrong function to free memory will get you a core dump. For example,
if memory was allocated using \function{PyMem_New()}, it has to be
freed using \function{PyMem_Del()}, not \function{free()}. A few
modules included with Python fell afoul of this and had to be fixed;
doubtless there are more third-party modules that will have the same
problem.
wrong function to free memory may get you a core dump. For example,
if memory was allocated using \function{PyObject_Malloc()}, it has to
be freed using \function{PyObject_Free()}, not \function{free()}. A
few modules included with Python fell afoul of this and had to be
fixed; doubtless there are more third-party modules that will have the
same problem.
As part of this change, the confusing multiple interfaces for
allocating memory have been consolidated down into two APIs.
Memory allocated with one API must not be freed with the other API.
allocating memory have been consolidated down into two API families.
Memory allocated with one family must not be manipulated with
functions from the other family.
There is another family of functions specifically for allocating
Python \emph{objects} (as opposed to memory).
\begin{itemize}
\item To allocate and free an undistinguished chunk of memory using
Python's allocator, use
\cfunction{PyMem_Malloc()}, \cfunction{PyMem_Realloc()}, and
\cfunction{PyMem_Free()}.
\item To allocate and free an undistinguished chunk of memory use
the ``raw memory'' family: \cfunction{PyMem_Malloc()},
\cfunction{PyMem_Realloc()}, and \cfunction{PyMem_Free()}.
\item In rare cases you may want to avoid using Python's allocator
in order to allocate a chunk of memory;
use \cfunction{PyObject_Malloc}, \cfunction{PyObject_Realloc},
and \cfunction{PyObject_Free}.
\item The ``object memory'' family is the interface to the pymalloc
facility described above and is biased towards a large number of
``small'' allocations: \cfunction{PyObject_Malloc},
\cfunction{PyObject_Realloc}, and \cfunction{PyObject_Free}.
\item To allocate and free Python objects,
use \cfunction{PyObject_New()}, \cfunction{PyObject_NewVar()}, and
\item To allocate and free Python objects, use the ``object'' family
\cfunction{PyObject_New()}, \cfunction{PyObject_NewVar()}, and
\cfunction{PyObject_Del()}.
\end{itemize}
Thanks to lots of work by Tim Peters, pymalloc in 2.3 also provides
@ -412,6 +415,13 @@ both extension modules and in the interpreter itself. To enable this
support, turn on the Python interpreter's debugging code by running
\program{configure} with \longprogramopt{with-pydebug}.
To aid extension writers, a header file \file{Misc/pymemcompat.h} is
distributed with the source to Python 2.3 that allows Python
extensions to use the 2.3 interfaces to memory allocation and compile
against any version of Python since 1.5.2. (The idea is that you take
the file from Python's source distribution and bundle it with the
source of you extension).
\begin{seealso}
\seeurl{http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/python/python/dist/src/Objects/obmalloc.c}