Include/pymem.h

   1 /* The PyMem_ family:  low-level memory allocation interfaces.
   2    See objimpl.h for the PyObject_ memory family.
   3 */
   4
   5 #ifndef Py_PYMEM_H
   6 #define Py_PYMEM_H
   7
   8 #include "pyport.h"
   9
  10 #ifdef __cplusplus
  11 extern "C" {
  12 #endif
  13
  14 /* BEWARE:
  15
  16    Each interface exports both functions and macros.  Extension modules should
  17    use the functions, to ensure binary compatibility across Python versions.
  18    Because the Python implementation is free to change internal details, and
  19    the macros may (or may not) expose details for speed, if you do use the
  20    macros you must recompile your extensions with each Python release.
  21
  22    Never mix calls to PyMem_ with calls to the platform malloc/realloc/
  23    calloc/free.  For example, on Windows different DLLs may end up using
  24    different heaps, and if you use PyMem_Malloc you'll get the memory from the
  25    heap used by the Python DLL; it could be a disaster if you free()'ed that
  26    directly in your own extension.  Using PyMem_Free instead ensures Python
  27    can return the memory to the proper heap.  As another example, in
  28    PYMALLOC_DEBUG mode, Python wraps all calls to all PyMem_ and PyObject_
  29    memory functions in special debugging wrappers that add additional
  30    debugging info to dynamic memory blocks.  The system routines have no idea
  31    what to do with that stuff, and the Python wrappers have no idea what to do
  32    with raw blocks obtained directly by the system routines then.
  33
  34    The GIL must be held when using these APIs.
  35 */
  36
  37 /*
  38  * Raw memory interface
  39  * ====================
  40  */
  41
  42 /* Functions
  43
  44    Functions supplying platform-independent semantics for malloc/realloc/
  45    free.  These functions make sure that allocating 0 bytes returns a distinct
  46    non-NULL pointer (whenever possible -- if we're flat out of memory, NULL
  47    may be returned), even if the platform malloc and realloc don't.
  48    Returned pointers must be checked for NULL explicitly.  No action is
  49    performed on failure (no exception is set, no warning is printed, etc).
  50 */
  51
  52 PyAPI_FUNC(void *) PyMem_Malloc(size_t);
  53 PyAPI_FUNC(void *) PyMem_Realloc(void *, size_t);
  54 PyAPI_FUNC(void) PyMem_Free(void *);
  55
  56 /* Starting from Python 1.6, the wrappers Py_{Malloc,Realloc,Free} are
  57    no longer supported. They used to call PyErr_NoMemory() on failure. */
  58
  59 /* Macros. */
  60 #ifdef PYMALLOC_DEBUG
  61 /* Redirect all memory operations to Python's debugging allocator. */
  62 #define PyMem_MALLOC            _PyMem_DebugMalloc
  63 #define PyMem_REALLOC           _PyMem_DebugRealloc
  64 #define PyMem_FREE              _PyMem_DebugFree
  65
  66 #else   /* ! PYMALLOC_DEBUG */
  67
  68 /* PyMem_MALLOC(0) means malloc(1). Some systems would return NULL
  69    for malloc(0), which would be treated as an error. Some platforms
  70    would return a pointer with no memory behind it, which would break
  71    pymalloc. To solve these problems, allocate an extra byte. */
  72 /* Returns NULL to indicate error if a negative size or size larger than
  73    Py_ssize_t can represent is supplied.  Helps prevents security holes. */
  74 #define PyMem_MALLOC(n)         (((n) < 0 || (n) > PY_SSIZE_T_MAX) ? NULL \
  75                                 : malloc((n) ? (n) : 1))
  76 #define PyMem_REALLOC(p, n)     (((n) < 0 || (n) > PY_SSIZE_T_MAX) ? NULL \
  77                                 : realloc((p), (n) ? (n) : 1))
  78 #define PyMem_FREE              free
  79
  80 #endif  /* PYMALLOC_DEBUG */
  81
  82 /*
  83  * Type-oriented memory interface
  84  * ==============================
  85  *
  86  * Allocate memory for n objects of the given type.  Returns a new pointer
  87  * or NULL if the request was too large or memory allocation failed.  Use
  88  * these macros rather than doing the multiplication yourself so that proper
  89  * overflow checking is always done.
  90  */
  91
  92 #define PyMem_New(type, n) \
  93   ( ((n) > PY_SSIZE_T_MAX / sizeof(type)) ? NULL : \
  94         ( (type *) PyMem_Malloc((n) * sizeof(type)) ) )
  95 #define PyMem_NEW(type, n) \
  96   ( ((n) > PY_SSIZE_T_MAX / sizeof(type)) ? NULL : \
  97         ( (type *) PyMem_MALLOC((n) * sizeof(type)) ) )
  98
  99 /*
 100  * The value of (p) is always clobbered by this macro regardless of success.
 101  * The caller MUST check if (p) is NULL afterwards and deal with the memory
 102  * error if so.  This means the original value of (p) MUST be saved for the
 103  * caller's memory error handler to not lose track of it.
 104  */
 105 #define PyMem_Resize(p, type, n) \
 106   ( (p) = ((n) > PY_SSIZE_T_MAX / sizeof(type)) ? NULL : \
 107         (type *) PyMem_Realloc((p), (n) * sizeof(type)) )
 108 #define PyMem_RESIZE(p, type, n) \
 109   ( (p) = ((n) > PY_SSIZE_T_MAX / sizeof(type)) ? NULL : \
 110         (type *) PyMem_REALLOC((p), (n) * sizeof(type)) )
 111
 112 /* PyMem{Del,DEL} are left over from ancient days, and shouldn't be used
 113  * anymore.  They're just confusing aliases for PyMem_{Free,FREE} now.
 114  */
 115 #define PyMem_Del               PyMem_Free
 116 #define PyMem_DEL               PyMem_FREE
 117
 118 #ifdef __cplusplus
 119 }
 120 #endif
 121
 122 #endif /* !Py_PYMEM_H */