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[Bug #580462] Mention changes to GC API 

Mention portable strptime()
Move C-level sections farther down in the file
This commit is contained in:
Andrew M. Kuchling 2002-07-22 19:21:06 +00:00
parent a982eb1eb5
commit ef5d06bd3f
1 changed files with 116 additions and 84 deletions
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Doc/whatsnew/whatsnew23.tex
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@ -17,8 +17,6 @@
%
% Bug #580462: changes to GC API
%
% Pure Python strptime implementation by Brett Cannon. See SF patch 474274.
%
%\section{Introduction \label{intro}}
@ -602,88 +600,6 @@ In 2.3, you get this:
\end{itemize}
%======================================================================
\section{Specialized Object Allocator (pymalloc)\label{section-pymalloc}}
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 \cfunction{malloc()} and have
less memory overhead for typical allocation patterns of Python
programs. The allocator uses C's \cfunction{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
\longprogramopt{with-pymalloc} option to the \program{configure}
script. In 2.3, pymalloc has had further enhancements and is now
enabled by default; you'll have to supply
\longprogramopt{without-pymalloc} to disable it.
This change is transparent to code written in Python; however,
pymalloc may expose bugs in C extensions. Authors of C extension
modules should test their code with the object allocator enabled,
because some incorrect code may cause core dumps at runtime. There
are a bunch of memory allocation functions in Python's C API that have
previously been just aliases for the C library's \cfunction{malloc()}
and \cfunction{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
\cfunction{malloc()} and \cfunction{free()} any more, and calling the
wrong function to free memory may get you a core dump. For example,
if memory was allocated using \cfunction{PyObject_Malloc()}, it has to
be freed using \cfunction{PyObject_Free()}, not \cfunction{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 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 use
the ``raw memory'' family: \cfunction{PyMem_Malloc()},
\cfunction{PyMem_Realloc()}, and \cfunction{PyMem_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 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
debugging features to catch memory overwrites and doubled frees in
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. You would copy the file
from Python's source distribution and bundle it with the source of
your extension.
\begin{seealso}
\seeurl{http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/python/python/dist/src/Objects/obmalloc.c}
{For the full details of the pymalloc implementation, see
the comments at the top of the file \file{Objects/obmalloc.c} in the
Python source code. The above link points to the file within the
SourceForge CVS browser.}
\end{seealso}
%======================================================================
\section{New and Improved Modules}
@ -831,6 +747,13 @@ documentation for details.
% XXX add a link to the module docs?
(Contributed by Greg Ward.)
\item The \module{time} module's \function{strptime()} function has
long been an annoyance because it uses the platform C library's
\function{strptime()} implementation, and different platforms
sometimes have odd bugs. Brett Cannon contributed a portable
implementation that's written in pure Python, which should behave
identically on all platforms.
\item The DOM implementation
in \module{xml.dom.minidom} can now generate XML output in a
particular encoding, by specifying an optional encoding argument to
@ -839,6 +762,88 @@ the \method{toxml()} and \method{toprettyxml()} methods of DOM nodes.
\end{itemize}
%======================================================================
\section{Specialized Object Allocator (pymalloc)\label{section-pymalloc}}
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 \cfunction{malloc()} and have
less memory overhead for typical allocation patterns of Python
programs. The allocator uses C's \cfunction{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
\longprogramopt{with-pymalloc} option to the \program{configure}
script. In 2.3, pymalloc has had further enhancements and is now
enabled by default; you'll have to supply
\longprogramopt{without-pymalloc} to disable it.
This change is transparent to code written in Python; however,
pymalloc may expose bugs in C extensions. Authors of C extension
modules should test their code with the object allocator enabled,
because some incorrect code may cause core dumps at runtime. There
are a bunch of memory allocation functions in Python's C API that have
previously been just aliases for the C library's \cfunction{malloc()}
and \cfunction{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
\cfunction{malloc()} and \cfunction{free()} any more, and calling the
wrong function to free memory may get you a core dump. For example,
if memory was allocated using \cfunction{PyObject_Malloc()}, it has to
be freed using \cfunction{PyObject_Free()}, not \cfunction{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 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 use
the ``raw memory'' family: \cfunction{PyMem_Malloc()},
\cfunction{PyMem_Realloc()}, and \cfunction{PyMem_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 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
debugging features to catch memory overwrites and doubled frees in
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. You would copy the file
from Python's source distribution and bundle it with the source of
your extension.
\begin{seealso}
\seeurl{http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/python/python/dist/src/Objects/obmalloc.c}
{For the full details of the pymalloc implementation, see
the comments at the top of the file \file{Objects/obmalloc.c} in the
Python source code. The above link points to the file within the
SourceForge CVS browser.}
\end{seealso}
% ======================================================================
\section{Build and C API Changes}
@ -846,6 +851,33 @@ Changes to Python's build process and to the C API include:
\begin{itemize}
\item The C-level interface to the garbage collector has been changed,
to make it easier to write extension types that support garbage
collection, and to make it easier to debug misuses of the functions.
Various functions have slightly different semantics, so a bunch of
functions had to be renamed. Extensions that use the old API will
still compile but will \emph{not} participate in garbage collection,
so updating them for 2.3 should be considered fairly high priority.
To upgrade an extension module to the new API, perform the following
steps:
\begin{itemize}
\item Rename \cfunction{Py_TPFLAGS_GC} to \cfunction{PyTPFLAGS_HAVE_GC}.
\item Use \cfunction{PyObject_GC_New} or \cfunction{PyObject_GC_NewVar} to
allocate objects, and \cfunction{PyObject_GC_Del} to deallocate them.
\item Rename \cfunction{PyObject_GC_Init} to \cfunction{PyObject_GC_Track} and
\cfunction{PyObject_GC_Fini} to \cfunction{PyObject_GC_UnTrack}.
\item Remove \cfunction{PyGC_HEAD_SIZE} from object size calculations.
\item Remove calls to \cfunction{PyObject_AS_GC} and \cfunction{PyObject_FROM_GC}.
\end{itemize}
\item Python can now optionally be built as a shared library
(\file{libpython2.3.so}) by supplying \longprogramopt{enable-shared}
when running Python's \file{configure} script. (Contributed by Ondrej