Zarządzanie Pamięcią
********************


Skorowidz
=========

Zarządzanie pamięcią w Pythonie zakłada prywatną stertę zawierającą
wszystkie obiekty i struktury danych Pythona. Zarządzanie tą prywatną
stertą jest zapewniane wewnętrznie przez *zarządcę pamięci Pythona*.
Zarządca pamięci Pythona ma różne komponenty które radzą sobie z
różnymi aspektami dynamicznego przechowywania, jak współdzielenie,
segmentacja, alokacja wstępna i kieszeniowanie.

Na najniższym poziomie, przedmiot przydzielający pamięć "na-surowo"
zapewnia że będzie dość pamięci na prywatnej stercie dla przechowania
wszystkich związanych-z-językiem-pytonowskim danych przez
współdziałanie z zarządcą pamięci systemu operacyjnego. Ponad zarządcą
surowej pamięci, kilka szczególnych dla danych typów przedmiotów
zarządców operuje na tej samej stercie i wypełnia szczególne zasady
zarządzania pamięcią dostosowane do szczególnych własności każdego
rodzaju przedmiotu. Dla przykładu przedmioty liczb całkowitych są
zarządzane inaczej wewnątrz sterty niż ciągi znaków, krotki czy
słowniki gdyż liczby całkowite zakładają inne wymagania przechowywania
i wady i zalety prędkości/zajętej przestrzeni. Zarządca pamięcią
Pythona zatem odprawia pewną ilość nakładów pracy dla szczególnych dla
przedmiotów różnych typów zarządców, ale zapewnia że te drugie będą
operować wewnątrz ograniczeń prywatnej sterty.

It is important to understand that the management of the Python heap
is performed by the interpreter itself and that the user has no
control over it, even if they regularly manipulate object pointers to
memory blocks inside that heap.  The allocation of heap space for
Python objects and other internal buffers is performed on demand by
the Python memory manager through the Python/C API functions listed in
this document.

To avoid memory corruption, extension writers should never try to
operate on Python objects with the functions exported by the C
library: "malloc()", "calloc()", "realloc()" and "free()".  This will
result in  mixed calls between the C allocator and the Python memory
manager with fatal consequences, because they implement different
algorithms and operate on different heaps.  However, one may safely
allocate and release memory blocks with the C library allocator for
individual purposes, as shown in the following example:

   PyObject *res;
   char *buf = (char *) malloc(BUFSIZ); /* for I/O */

   if (buf == NULL)
       return PyErr_NoMemory();
   ...Do some I/O operation involving buf...
   res = PyBytes_FromString(buf);
   free(buf); /* malloc'ed */
   return res;

In this example, the memory request for the I/O buffer is handled by
the C library allocator. The Python memory manager is involved only in
the allocation of the bytes object returned as a result.

W większości przypadków, jednakże, zalecane jest umieszczanie w
pamięci ze sterty Pythona szczególnie ponieważ ta ostatnia jest pod
kontrolą zarządcy pamięci języka Pytonowskiego. Na przykład, jest to
wymagane gdy program interpretujący polecenia Pythona jest rozszerzany
nowymi typami obiektów napisanych w języku C. Inną przyczyną użycia
sterty Pythona jest chęć *poinformowania* zarządcy pamięci Pythona o
potrzebach pamięciowych modułu rozszerzającego. Nawet gdy żądana
pamięć jest używana wyłącznie dla wewnętrznych wysoko-
wyspecjalizowanych potrzeb, oddelegowanie wszystkich zapytań o pamięć
do zarządcy pamięci Pythona spowoduje że program interpretujący
polecenia Pythona będzie  miał  bardziej trafny obraz podstawowego
rozmiaru potrzeb pamięciowych jako całości. Konsekwentnie, w pewnych
warunkach zarządca pamięci Pythona może lub może nie uruchomić
właściwych działań, jak zbiórki śmieci, porządkowania pamięci lub
innych zapobiegawczych działań. Zauważ, że używając programu
bibliotecznego lokującego pamięć z języka C jak pokazano w poprzednim
przykładzie zarezerwowana pamięć dla obszaru wymiany wejścia/wyjścia
całkowicie umyka uwadze zarządcy pamięci Pythona.

Zobacz także:

  The "PYTHONMALLOC" environment variable can be used to configure the
  memory allocators used by Python.

  The "PYTHONMALLOCSTATS" environment variable can be used to print
  statistics of the pymalloc memory allocator every time a new
  pymalloc object arena is created, and on shutdown.


Raw Memory Interface
====================

The following function sets are wrappers to the system allocator.
These functions are thread-safe, the *GIL* does not need to be held.

The default raw memory allocator uses the following functions:
"malloc()", "calloc()", "realloc()" and "free()"; call "malloc(1)" (or
"calloc(1, 1)") when requesting zero bytes.

Nowe w wersji 3.4.

void* PyMem_RawMalloc(size_t n)

   Allocates *n* bytes and returns a pointer of type "void*" to the
   allocated memory, or "NULL" if the request fails.

   Requesting zero bytes returns a distinct non-"NULL" pointer if
   possible, as if "PyMem_RawMalloc(1)" had been called instead. The
   memory will not have been initialized in any way.

void* PyMem_RawCalloc(size_t nelem, size_t elsize)

   Allocates *nelem* elements each whose size in bytes is *elsize* and
   returns a pointer of type "void*" to the allocated memory, or
   "NULL" if the request fails. The memory is initialized to zeros.

   Requesting zero elements or elements of size zero bytes returns a
   distinct non-"NULL" pointer if possible, as if "PyMem_RawCalloc(1,
   1)" had been called instead.

   Nowe w wersji 3.5.

void* PyMem_RawRealloc(void *p, size_t n)

   Resizes the memory block pointed to by *p* to *n* bytes. The
   contents will be unchanged to the minimum of the old and the new
   sizes.

   If *p* is "NULL", the call is equivalent to "PyMem_RawMalloc(n)";
   else if *n* is equal to zero, the memory block is resized but is
   not freed, and the returned pointer is non-"NULL".

   Unless *p* is "NULL", it must have been returned by a previous call
   to "PyMem_RawMalloc()", "PyMem_RawRealloc()" or
   "PyMem_RawCalloc()".

   If the request fails, "PyMem_RawRealloc()" returns "NULL" and *p*
   remains a valid pointer to the previous memory area.

void PyMem_RawFree(void *p)

   Frees the memory block pointed to by *p*, which must have been
   returned by a previous call to "PyMem_RawMalloc()",
   "PyMem_RawRealloc()" or "PyMem_RawCalloc()".  Otherwise, or if
   "PyMem_RawFree(p)" has been called before, undefined behavior
   occurs.

   If *p* is "NULL", no operation is performed.


Sprzęg Pamięci
==============

The following function sets, modeled after the ANSI C standard, but
specifying behavior when requesting zero bytes, are available for
allocating and releasing memory from the Python heap.

The default memory allocator uses the pymalloc memory allocator.

Ostrzeżenie:

  The *GIL* must be held when using these functions.

Zmienione w wersji 3.6: The default allocator is now pymalloc instead
of system "malloc()".

void* PyMem_Malloc(size_t n)

   Allocates *n* bytes and returns a pointer of type "void*" to the
   allocated memory, or "NULL" if the request fails.

   Requesting zero bytes returns a distinct non-"NULL" pointer if
   possible, as if "PyMem_Malloc(1)" had been called instead. The
   memory will not have been initialized in any way.

void* PyMem_Calloc(size_t nelem, size_t elsize)

   Allocates *nelem* elements each whose size in bytes is *elsize* and
   returns a pointer of type "void*" to the allocated memory, or
   "NULL" if the request fails. The memory is initialized to zeros.

   Requesting zero elements or elements of size zero bytes returns a
   distinct non-"NULL" pointer if possible, as if "PyMem_Calloc(1, 1)"
   had been called instead.

   Nowe w wersji 3.5.

void* PyMem_Realloc(void *p, size_t n)

   Resizes the memory block pointed to by *p* to *n* bytes. The
   contents will be unchanged to the minimum of the old and the new
   sizes.

   If *p* is "NULL", the call is equivalent to "PyMem_Malloc(n)"; else
   if *n* is equal to zero, the memory block is resized but is not
   freed, and the returned pointer is non-"NULL".

   Unless *p* is "NULL", it must have been returned by a previous call
   to "PyMem_Malloc()", "PyMem_Realloc()" or "PyMem_Calloc()".

   If the request fails, "PyMem_Realloc()" returns "NULL" and *p*
   remains a valid pointer to the previous memory area.

void PyMem_Free(void *p)

   Frees the memory block pointed to by *p*, which must have been
   returned by a previous call to "PyMem_Malloc()", "PyMem_Realloc()"
   or "PyMem_Calloc()".  Otherwise, or if "PyMem_Free(p)" has been
   called before, undefined behavior occurs.

   If *p* is "NULL", no operation is performed.

Następujące makropolecenia zorientowane-według-typu dostarczone są dla
wygody. Zauważ że *TYP* odnosi się do dowolnego typu C.

TYPE* PyMem_New(TYPE, size_t n)

   Same as "PyMem_Malloc()", but allocates "(n * sizeof(TYPE))" bytes
   of memory.  Returns a pointer cast to "TYPE*".  The memory will not
   have been initialized in any way.

TYPE* PyMem_Resize(void *p, TYPE, size_t n)

   Same as "PyMem_Realloc()", but the memory block is resized to "(n *
   sizeof(TYPE))" bytes.  Returns a pointer cast to "TYPE*". On
   return, *p* will be a pointer to the new memory area, or "NULL" in
   the event of failure.

   This is a C preprocessor macro; *p* is always reassigned.  Save the
   original value of *p* to avoid losing memory when handling errors.

void PyMem_Del(void *p)

   Same as "PyMem_Free()".

Dodać należy, że następujący zbiór makropoleceń dostarczony jest aby
odwoływać się do programu przydzielającego pamięć w języku pytonowskim
bezpośrednio, bez udziału zadań sprzęgu C wymienionych powyżej.
Jednakże, zauważ, że ich użycie nie zachowuje wzajemnej zgodności
binarnej pomiędzy wersjami Pythona i z tego też powodu ich użycie jest
niewskazane w modułach rozszerzających.

* "PyMem_MALLOC(size)"

* "PyMem_NEW(type, size)"

* "PyMem_REALLOC(ptr, size)"

* "PyMem_RESIZE(ptr, type, size)"

* "PyMem_FREE(ptr)"

* "PyMem_DEL(ptr)"


Object allocators
=================

The following function sets, modeled after the ANSI C standard, but
specifying behavior when requesting zero bytes, are available for
allocating and releasing memory from the Python heap.

The default object allocator uses the pymalloc memory allocator.

Ostrzeżenie:

  The *GIL* must be held when using these functions.

void* PyObject_Malloc(size_t n)

   Allocates *n* bytes and returns a pointer of type "void*" to the
   allocated memory, or "NULL" if the request fails.

   Requesting zero bytes returns a distinct non-"NULL" pointer if
   possible, as if "PyObject_Malloc(1)" had been called instead. The
   memory will not have been initialized in any way.

void* PyObject_Calloc(size_t nelem, size_t elsize)

   Allocates *nelem* elements each whose size in bytes is *elsize* and
   returns a pointer of type "void*" to the allocated memory, or
   "NULL" if the request fails. The memory is initialized to zeros.

   Requesting zero elements or elements of size zero bytes returns a
   distinct non-"NULL" pointer if possible, as if "PyObject_Calloc(1,
   1)" had been called instead.

   Nowe w wersji 3.5.

void* PyObject_Realloc(void *p, size_t n)

   Resizes the memory block pointed to by *p* to *n* bytes. The
   contents will be unchanged to the minimum of the old and the new
   sizes.

   If *p* is "NULL", the call is equivalent to "PyObject_Malloc(n)";
   else if *n* is equal to zero, the memory block is resized but is
   not freed, and the returned pointer is non-"NULL".

   Unless *p* is "NULL", it must have been returned by a previous call
   to "PyObject_Malloc()", "PyObject_Realloc()" or
   "PyObject_Calloc()".

   If the request fails, "PyObject_Realloc()" returns "NULL" and *p*
   remains a valid pointer to the previous memory area.

void PyObject_Free(void *p)

   Frees the memory block pointed to by *p*, which must have been
   returned by a previous call to "PyObject_Malloc()",
   "PyObject_Realloc()" or "PyObject_Calloc()".  Otherwise, or if
   "PyObject_Free(p)" has been called before, undefined behavior
   occurs.

   If *p* is "NULL", no operation is performed.


Default Memory Allocators
=========================

Default memory allocators:

+---------------------------------+----------------------+--------------------+-----------------------+----------------------+
| Configuration                   | Nazwa                | PyMem_RawMalloc    | PyMem_Malloc          | PyObject_Malloc      |
|=================================|======================|====================|=======================|======================|
| Release build                   | ""pymalloc""         | "malloc"           | "pymalloc"            | "pymalloc"           |
+---------------------------------+----------------------+--------------------+-----------------------+----------------------+
| Debug build                     | ""pymalloc_debug""   | "malloc" + debug   | "pymalloc" + debug    | "pymalloc" + debug   |
+---------------------------------+----------------------+--------------------+-----------------------+----------------------+
| Release build, without pymalloc | ""malloc""           | "malloc"           | "malloc"              | "malloc"             |
+---------------------------------+----------------------+--------------------+-----------------------+----------------------+
| Debug build, without pymalloc   | ""malloc_debug""     | "malloc" + debug   | "malloc" + debug      | "malloc" + debug     |
+---------------------------------+----------------------+--------------------+-----------------------+----------------------+

Legend:

* Name: value for "PYTHONMALLOC" environment variable

* "malloc": system allocators from the standard C library, C
  functions: "malloc()", "calloc()", "realloc()" and "free()"

* "pymalloc": pymalloc memory allocator

* "+ debug": with debug hooks installed by "PyMem_SetupDebugHooks()"


Customize Memory Allocators
===========================

Nowe w wersji 3.4.

PyMemAllocatorEx

   Structure used to describe a memory block allocator. The structure
   has the following fields:

   +------------------------------------------------------------+-----------------------------------------+
   | Field                                                      | Znaczenie                               |
   |============================================================|=========================================|
   | "void *ctx"                                                | user context passed as first argument   |
   +------------------------------------------------------------+-----------------------------------------+
   | "void* malloc(void *ctx, size_t size)"                     | allocate a memory block                 |
   +------------------------------------------------------------+-----------------------------------------+
   | "void* calloc(void *ctx, size_t nelem, size_t elsize)"     | allocate a memory block initialized     |
   |                                                            | with zeros                              |
   +------------------------------------------------------------+-----------------------------------------+
   | "void* realloc(void *ctx, void *ptr, size_t new_size)"     | allocate or resize a memory block       |
   +------------------------------------------------------------+-----------------------------------------+
   | "void free(void *ctx, void *ptr)"                          | free a memory block                     |
   +------------------------------------------------------------+-----------------------------------------+

   Zmienione w wersji 3.5: The "PyMemAllocator" structure was renamed
   to "PyMemAllocatorEx" and a new "calloc" field was added.

PyMemAllocatorDomain

   Enum used to identify an allocator domain. Domains:

   PYMEM_DOMAIN_RAW

      Functions:

      * "PyMem_RawMalloc()"

      * "PyMem_RawRealloc()"

      * "PyMem_RawCalloc()"

      * "PyMem_RawFree()"

   PYMEM_DOMAIN_MEM

      Functions:

      * "PyMem_Malloc()",

      * "PyMem_Realloc()"

      * "PyMem_Calloc()"

      * "PyMem_Free()"

   PYMEM_DOMAIN_OBJ

      Functions:

      * "PyObject_Malloc()"

      * "PyObject_Realloc()"

      * "PyObject_Calloc()"

      * "PyObject_Free()"

void PyMem_GetAllocator(PyMemAllocatorDomain domain, PyMemAllocatorEx *allocator)

   Get the memory block allocator of the specified domain.

void PyMem_SetAllocator(PyMemAllocatorDomain domain, PyMemAllocatorEx *allocator)

   Set the memory block allocator of the specified domain.

   The new allocator must return a distinct non-"NULL" pointer when
   requesting zero bytes.

   For the "PYMEM_DOMAIN_RAW" domain, the allocator must be thread-
   safe: the *GIL* is not held when the allocator is called.

   If the new allocator is not a hook (does not call the previous
   allocator), the "PyMem_SetupDebugHooks()" function must be called
   to reinstall the debug hooks on top on the new allocator.

void PyMem_SetupDebugHooks(void)

   Setup hooks to detect bugs in the Python memory allocator
   functions.

   Newly allocated memory is filled with the byte "0xCD"
   ("CLEANBYTE"), freed memory is filled with the byte "0xDD"
   ("DEADBYTE"). Memory blocks are surrounded by "forbidden bytes"
   ("FORBIDDENBYTE": byte "0xFD").

   Runtime checks:

   * Detect API violations, ex: "PyObject_Free()" called on a buffer
     allocated by "PyMem_Malloc()"

   * Detect write before the start of the buffer (buffer underflow)

   * Detect write after the end of the buffer (buffer overflow)

   * Check that the *GIL* is held when allocator functions of
     "PYMEM_DOMAIN_OBJ" (ex: "PyObject_Malloc()") and
     "PYMEM_DOMAIN_MEM" (ex: "PyMem_Malloc()") domains are called

   On error, the debug hooks use the "tracemalloc" module to get the
   traceback where a memory block was allocated. The traceback is only
   displayed if "tracemalloc" is tracing Python memory allocations and
   the memory block was traced.

   These hooks are installed by default if Python is compiled in debug
   mode. The "PYTHONMALLOC" environment variable can be used to
   install debug hooks on a Python compiled in release mode.

   Zmienione w wersji 3.6: This function now also works on Python
   compiled in release mode. On error, the debug hooks now use
   "tracemalloc" to get the traceback where a memory block was
   allocated. The debug hooks now also check if the GIL is held when
   functions of "PYMEM_DOMAIN_OBJ" and "PYMEM_DOMAIN_MEM" domains are
   called.

   Zmienione w wersji 3.8: Byte patterns "0xCB" ("CLEANBYTE"), "0xDB"
   ("DEADBYTE") and "0xFB" ("FORBIDDENBYTE") have been replaced with
   "0xCD", "0xDD" and "0xFD" to use the same values than Windows CRT
   debug "malloc()" and "free()".


The pymalloc allocator
======================

Python has a *pymalloc* allocator optimized for small objects (smaller
or equal to 512 bytes) with a short lifetime. It uses memory mappings
called "arenas" with a fixed size of 256 KiB. It falls back to
"PyMem_RawMalloc()" and "PyMem_RawRealloc()" for allocations larger
than 512 bytes.

*pymalloc* is the default allocator of the "PYMEM_DOMAIN_MEM" (ex:
"PyMem_Malloc()") and "PYMEM_DOMAIN_OBJ" (ex: "PyObject_Malloc()")
domains.

The arena allocator uses the following functions:

* "VirtualAlloc()" and "VirtualFree()" on Windows,

* "mmap()" and "munmap()" if available,

* "malloc()" and "free()" otherwise.


Customize pymalloc Arena Allocator
----------------------------------

Nowe w wersji 3.4.

PyObjectArenaAllocator

   Structure used to describe an arena allocator. The structure has
   three fields:

   +----------------------------------------------------+-----------------------------------------+
   | Field                                              | Znaczenie                               |
   |====================================================|=========================================|
   | "void *ctx"                                        | user context passed as first argument   |
   +----------------------------------------------------+-----------------------------------------+
   | "void* alloc(void *ctx, size_t size)"              | allocate an arena of size bytes         |
   +----------------------------------------------------+-----------------------------------------+
   | "void free(void *ctx, void *ptr, size_t size)"     | free an arena                           |
   +----------------------------------------------------+-----------------------------------------+

void PyObject_GetArenaAllocator(PyObjectArenaAllocator *allocator)

   Get the arena allocator.

void PyObject_SetArenaAllocator(PyObjectArenaAllocator *allocator)

   Set the arena allocator.


tracemalloc C API
=================

Nowe w wersji 3.7.

int PyTraceMalloc_Track(unsigned int domain, uintptr_t ptr, size_t size)

   Track an allocated memory block in the "tracemalloc" module.

   Return "0" on success, return "-1" on error (failed to allocate
   memory to store the trace). Return "-2" if tracemalloc is disabled.

   If memory block is already tracked, update the existing trace.

int PyTraceMalloc_Untrack(unsigned int domain, uintptr_t ptr)

   Untrack an allocated memory block in the "tracemalloc" module. Do
   nothing if the block was not tracked.

   Return "-2" if tracemalloc is disabled, otherwise return "0".


Przykłady
=========

Tutaj jest przykład z sekcji "przeglądu pamięci" - z ang. - Skorowidz,
przepisane, tak aby przestrzeń wejścia/wyjścia była przydzielona ze
sterty Pythona używając pierwszego zestawu zadań:

   PyObject *res;
   char *buf = (char *) PyMem_Malloc(BUFSIZ); /* for I/O */

   if (buf == NULL)
       return PyErr_NoMemory();
   /* ...Do some I/O operation involving buf... */
   res = PyBytes_FromString(buf);
   PyMem_Free(buf); /* allocated with PyMem_Malloc */
   return res;

ten sam kod przy użyciu zorientowanych na typ zbiorów zadań:

   PyObject *res;
   char *buf = PyMem_New(char, BUFSIZ); /* for I/O */

   if (buf == NULL)
       return PyErr_NoMemory();
   /* ...Do some I/O operation involving buf... */
   res = PyBytes_FromString(buf);
   PyMem_Del(buf); /* allocated with PyMem_New */
   return res;

Zauważ, że w dwóch powyższych przykładach, przestrzeń wymiany jest
zawsze zmieniana przez zadania należące do tego samego zbioru.
Właściwie, jest wymagane użycie tej samej rodziny sprzęgów zarządzania
pamięcią (z ang. - memory API) dla danego obszaru pamięci, tak, że
ryzyko pomieszania różnych programów lokujących zmniejszone jest do
minimum. Następująca sekwencja zawiera dwa błędy, jeden z których
określony jest jako *krytyczny* ponieważ miesza dwa różne programy
lokujące pamięć działające na różnych stertach.

   char *buf1 = PyMem_New(char, BUFSIZ);
   char *buf2 = (char *) malloc(BUFSIZ);
   char *buf3 = (char *) PyMem_Malloc(BUFSIZ);
   ...
   PyMem_Del(buf3);  /* Wrong -- should be PyMem_Free() */
   free(buf2);       /* Right -- allocated via malloc() */
   free(buf1);       /* Fatal -- should be PyMem_Del()  */

In addition to the functions aimed at handling raw memory blocks from
the Python heap, objects in Python are allocated and released with
"PyObject_New()", "PyObject_NewVar()" and "PyObject_Del()".

Te zostaną wyjaśnione w następnym rozdziale o określaniu i
realizowaniu nowych typów obiektów w języku C.
