cpython/Include/pymem.h

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/* Lowest-level memory allocation interface */
#ifndef Py_PYMEM_H
#define Py_PYMEM_H
#include "pyport.h"
#ifdef __cplusplus
extern "C" {
#endif
/* BEWARE:
Each interface exports both functions and macros. Extension modules
should normally use the functions for ensuring binary compatibility
of the user's code across Python versions. Subsequently, if the
Python runtime switches to its own malloc (different from standard
malloc), no recompilation is required for the extensions.
The macro versions are free to trade compatibility for speed, although
there's no guarantee they're ever faster. Extensions shouldn't use the
macro versions, as they don't gurantee binary compatibility across
releases.
Do not mix calls to PyMem_xyz with calls to platform
malloc/realloc/calloc/free. */
/*
* Raw memory interface
* ====================
*/
/* Functions */
/* Functions supplying platform-independent semantics for malloc/realloc/
free; useful if you need to be sure you're using the same memory
allocator as Python (this can be especially important on Windows, if
you need to make sure you're using the same MS malloc/free, and out of
the same heap, as the main Python DLL uses).
These functions make sure that allocating 0 bytes returns a distinct
non-NULL pointer (whenever possible -- if we're flat out of memory, NULL
may be returned), even if the platform malloc and realloc don't.
Returned pointers must be checked for NULL explicitly. No action is
performed on failure (no exception is set, no warning is printed, etc).` */
extern DL_IMPORT(void *) PyMem_Malloc(size_t);
extern DL_IMPORT(void *) PyMem_Realloc(void *, size_t);
extern DL_IMPORT(void) PyMem_Free(void *);
/* Starting from Python 1.6, the wrappers Py_{Malloc,Realloc,Free} are
no longer supported. They used to call PyErr_NoMemory() on failure. */
/* Macros. */
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#ifndef PyMem_MALLOC
#ifdef MALLOC_ZERO_RETURNS_NULL
#define PyMem_MALLOC(n) malloc((n) ? (n) : 1)
#else
#define PyMem_MALLOC malloc
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#endif
/* Caution: whether MALLOC_ZERO_RETURNS_NULL is #defined has nothing to
do with whether platform realloc(non-NULL, 0) normally frees the memory
or returns NULL. Rather than introduce yet another config variation,
just make a realloc to 0 bytes act as if to 1 instead. */
#define PyMem_REALLOC(p, n) realloc((p), (n) ? (n) : 1)
#define PyMem_FREE free
#endif /* PyMem_MALLOC */
/*
* Type-oriented memory interface
* ==============================
*
* These are carried along for historical reasons. There's rarely a good
* reason to use them anymore.
*/
/* Functions */
#define PyMem_New(type, n) \
( (type *) PyMem_Malloc((n) * sizeof(type)) )
#define PyMem_Resize(p, type, n) \
( (p) = (type *) PyMem_Realloc((p), (n) * sizeof(type)) )
/* In order to avoid breaking old code mixing PyObject_{New, NEW} with
PyMem_{Del, DEL} (there was no choice about this in 1.5.2), the latter
have to be redirected to the object allocator. */
/* XXX The parser module needs rework before this can be enabled. */
#if 0
#define PyMem_Del PyObject_Free
#else
#define PyMem_Del PyMem_Free
#endif
/* Macros */
#define PyMem_NEW(type, n) \
( (type *) PyMem_MALLOC((n) * sizeof(type)) )
#define PyMem_RESIZE(p, type, n) \
( (p) = (type *) PyMem_REALLOC((p), (n) * sizeof(type)) )
/* XXX The parser module needs rework before this can be enabled. */
#if 0
#define PyMem_DEL PyObject_FREE
#else
#define PyMem_DEL PyMem_FREE
#endif
Give Python a debug-mode pymalloc, much as sketched on Python-Dev. When WITH_PYMALLOC is defined, define PYMALLOC_DEBUG to enable the debug allocator. This can be done independent of build type (release or debug). A debug build automatically defines PYMALLOC_DEBUG when pymalloc is enabled. It's a detected error to define PYMALLOC_DEBUG when pymalloc isn't enabled. Two debugging entry points defined only under PYMALLOC_DEBUG: + _PyMalloc_DebugCheckAddress(const void *p) can be used (e.g., from gdb) to sanity-check a memory block obtained from pymalloc. It sprays info to stderr (see next) and dies via Py_FatalError if the block is detectably damaged. + _PyMalloc_DebugDumpAddress(const void *p) can be used to spray info about a debug memory block to stderr. A tiny start at implementing "API family" checks isn't good for anything yet. _PyMalloc_DebugRealloc() has been optimized to do little when the new size is <= old size. However, if the new size is larger, it really can't call the underlying realloc() routine without either violating its contract, or knowing something non-trivial about how the underlying realloc() works. A memcpy is always done in this case. This was a disaster for (and only) one of the std tests: test_bufio creates single text file lines up to a million characters long. On Windows, fileobject.c's get_line() uses the horridly funky getline_via_fgets(), which keeps growing and growing a string object hoping to find a newline. It grew the string object 1000 bytes each time, so for a million-character string it took approximately forever (I gave up after a few minutes). So, also: fileobject.c, getline_via_fgets(): When a single line is outrageously long, grow the string object at a mildly exponential rate, instead of just 1000 bytes at a time. That's enough so that a debug-build test_bufio finishes in about 5 seconds on my Win98SE box. I'm curious to try this on Win2K, because it has very different memory behavior than Win9X, and test_bufio always took a factor of 10 longer to complete on Win2K. It *could* be that the endless reallocs were simply killing it on Win2K even in the release build.
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#ifdef __cplusplus
}
#endif
#endif /* !Py_PYMEM_H */