cpython/Include/pymem.h

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/* The PyMem_ family: low-level memory allocation interfaces.
See objimpl.h for the PyObject_ memory family.
*/
#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
use the functions, to ensure binary compatibility across Python versions.
Because the Python implementation is free to change internal details, and
the macros may (or may not) expose details for speed, if you do use the
macros you must recompile your extensions with each Python release.
Never mix calls to PyMem_ with calls to the platform malloc/realloc/
calloc/free. For example, on Windows different DLLs may end up using
different heaps, and if you use PyMem_Malloc you'll get the memory from the
heap used by the Python DLL; it could be a disaster if you free()'ed that
directly in your own extension. Using PyMem_Free instead ensures Python
can return the memory to the proper heap. As another example, in
PYMALLOC_DEBUG mode, Python wraps all calls to all PyMem_ and PyObject_
memory functions in special debugging wrappers that add additional
debugging info to dynamic memory blocks. The system routines have no idea
what to do with that stuff, and the Python wrappers have no idea what to do
with raw blocks obtained directly by the system routines then.
The GIL must be held when using these APIs.
*/
/*
* Raw memory interface
* ====================
*/
/* Functions
Functions supplying platform-independent semantics for malloc/realloc/
free. 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).
*/
PyAPI_FUNC(void *) PyMem_Malloc(size_t);
PyAPI_FUNC(void *) PyMem_Realloc(void *, size_t);
PyAPI_FUNC(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. */
#ifdef PYMALLOC_DEBUG
/* Redirect all memory operations to Python's debugging allocator. */
#define PyMem_MALLOC PyObject_MALLOC
#define PyMem_REALLOC PyObject_REALLOC
#define PyMem_FREE PyObject_FREE
#else /* ! PYMALLOC_DEBUG */
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/* PyMem_MALLOC(0) means malloc(1). Some systems would return NULL
for malloc(0), which would be treated as an error. Some platforms
would return a pointer with no memory behind it, which would break
pymalloc. To solve these problems, allocate an extra byte. */
/* Returns NULL to indicate error if a negative size or size larger than
Py_ssize_t can represent is supplied. Helps prevents security holes. */
#define PyMem_MALLOC(n) (((n) < 0 || (n) > PY_SSIZE_T_MAX) ? NULL \
: malloc((n) ? (n) : 1))
#define PyMem_REALLOC(p, n) (((n) < 0 || (n) > PY_SSIZE_T_MAX) ? NULL \
: realloc((p), (n) ? (n) : 1))
#define PyMem_FREE free
#endif /* PYMALLOC_DEBUG */
/*
* Type-oriented memory interface
* ==============================
*
* Allocate memory for n objects of the given type. Returns a new pointer
* or NULL if the request was too large or memory allocation failed. Use
* these macros rather than doing the multiplication yourself so that proper
* overflow checking is always done.
*/
#define PyMem_New(type, n) \
( ((size_t)(n) > PY_SSIZE_T_MAX / sizeof(type)) ? NULL : \
( (type *) PyMem_Malloc((n) * sizeof(type)) ) )
#define PyMem_NEW(type, n) \
( ((size_t)(n) > PY_SSIZE_T_MAX / sizeof(type)) ? NULL : \
( (type *) PyMem_MALLOC((n) * sizeof(type)) ) )
/*
* The value of (p) is always clobbered by this macro regardless of success.
* The caller MUST check if (p) is NULL afterwards and deal with the memory
* error if so. This means the original value of (p) MUST be saved for the
* caller's memory error handler to not lose track of it.
*/
#define PyMem_Resize(p, type, n) \
( (p) = ((size_t)(n) > PY_SSIZE_T_MAX / sizeof(type)) ? NULL : \
(type *) PyMem_Realloc((p), (n) * sizeof(type)) )
#define PyMem_RESIZE(p, type, n) \
( (p) = ((size_t)(n) > PY_SSIZE_T_MAX / sizeof(type)) ? NULL : \
(type *) PyMem_REALLOC((p), (n) * sizeof(type)) )
/* PyMem{Del,DEL} are left over from ancient days, and shouldn't be used
* anymore. They're just confusing aliases for PyMem_{Free,FREE} now.
*/
#define PyMem_Del PyMem_Free
#define PyMem_DEL PyMem_FREE
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 */