Gerenciamento de Memória
************************


Visão Geral
===========

O gerenciamento de memória em Python envolve um heap privado contendo
todos os objetos e estruturas de dados Python. O gerenciamento desse
heap privado é garantido internamente pelo *gerenciador de memória do
Python*. O gerenciador de memória do Python possui diferentes
componentes que lidam com diversos aspectos dinâmicos do gerenciamento
de armazenamento, como compartilhamento, segmentação, pré-alocação ou
cache.

No nível mais baixo, um alocador de memória bruta garante que haja
espaço suficiente no heap privado para armazenar todos os dados
relacionados ao Python, interagindo com o gerenciador de memória do
sistema operacional. Além do alocador de memória bruta, vários
alocadores específicos de objeto operam no mesmo heap e implementam
políticas distintas de gerenciamento de memória, adaptadas às
peculiaridades de cada tipo de objeto. Por exemplo, objetos inteiros
são gerenciados dentro do heap de forma diferente de strings, tuplas
ou dicionários, pois inteiros implicam diferentes requisitos de
armazenamento e compensações entre velocidade e espaço. O gerenciador
de memória do Python, portanto, delega parte do trabalho aos
alocadores específicos de objeto, mas garante que estes operem dentro
dos limites do heap privado.

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.

In most situations, however, it is recommended to allocate memory from
the Python heap specifically because the latter is under control of
the Python memory manager. For example, this is required when the
interpreter is extended with new object types written in C. Another
reason for using the Python heap is the desire to *inform* the Python
memory manager about the memory needs of the extension module. Even
when the requested memory is used exclusively for internal, highly
specific purposes, delegating all memory requests to the Python memory
manager causes the interpreter to have a more accurate image of its
memory footprint as a whole. Consequently, under certain
circumstances, the Python memory manager may or may not trigger
appropriate actions, like garbage collection, memory compaction or
other preventive procedures. Note that by using the C library
allocator as shown in the previous example, the allocated memory for
the I/O buffer escapes completely the Python memory manager.

Ver também:

  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.


Allocator Domains
=================

All allocating functions belong to one of three different "domains"
(see also "PyMemAllocatorDomain"). These domains represent different
allocation strategies and are optimized for different purposes. The
specific details on how every domain allocates memory or what internal
functions each domain calls is considered an implementation detail,
but for debugging purposes a simplified table can be found at here.
The APIs used to allocate and free a block of memory must be from the
same domain. For example, "PyMem_Free()" must be used to free memory
allocated using "PyMem_Malloc()".

The three allocation domains are:

* Raw domain: intended for allocating memory for general-purpose
  memory buffers where the allocation *must* go to the system
  allocator or where the allocator can operate without an *attached
  thread state*. The memory is requested directly from the system. See
  Raw Memory Interface.

* "Mem" domain: intended for allocating memory for Python buffers and
  general-purpose memory buffers where the allocation must be
  performed with an *attached thread state*. The memory is taken from
  the Python private heap. See Memory Interface.

* Object domain: intended for allocating memory for Python objects.
  The memory is taken from the Python private heap. See Object
  allocators.

Nota:

  The *free-threaded* build requires that only Python objects are
  allocated using the "object" domain and that all Python objects are
  allocated using that domain. This differs from the prior Python
  versions, where this was only a best practice and not a hard
  requirement.For example, buffers (non-Python objects) should be
  allocated using "PyMem_Malloc()", "PyMem_RawMalloc()", or
  "malloc()", but not "PyObject_Malloc()".See Memory Allocation APIs.


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

The following function sets are wrappers to the system allocator.
These functions are thread-safe, so a *thread state* does not need to
be *attached*.

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.

Adicionado na versão 3.4.

void *PyMem_RawMalloc(size_t n)
    * Parte da ABI Estável desde a versão 3.13.*

   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)
    * Parte da ABI Estável desde a versão 3.13.*

   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.

   Adicionado na versão 3.5.

void *PyMem_RawRealloc(void *p, size_t n)
    * Parte da ABI Estável desde a versão 3.13.*

   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)
    * Parte da ABI Estável desde a versão 3.13.*

   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.


Interface da Memória
====================

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.

Aviso:

  There must be an *attached thread state* when using these functions.

Alterado na versão 3.6: The default allocator is now pymalloc instead
of system "malloc()".

void *PyMem_Malloc(size_t n)
    * Parte da ABI Estável.*

   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)
    * Parte da ABI Estável desde a versão 3.7.*

   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.

   Adicionado na versão 3.5.

void *PyMem_Realloc(void *p, size_t n)
    * Parte da ABI Estável.*

   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)
    * Parte da ABI Estável.*

   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.

The following type-oriented macros are provided for convenience.  Note
that *TYPE* refers to any C type.

PyMem_New(TYPE, 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.

PyMem_Resize(p, TYPE, 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()".

Além disso, os seguintes conjuntos de macros são fornecidos para
chamar o alocador de memória do Python diretamente, sem envolver as
funções da API C listadas acima. No entanto, observe que seu uso não
preserva a compatibilidade binária entre as versões do Python e,
portanto, está descontinuado em módulos de extensão.

* "PyMem_MALLOC(size)"

* "PyMem_NEW(type, size)"

* "PyMem_REALLOC(ptr, size)"

* "PyMem_RESIZE(ptr, type, size)"

* "PyMem_FREE(ptr)"

* "PyMem_DEL(ptr)"


Alocadores de objeto
====================

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.

Nota:

  There is no guarantee that the memory returned by these allocators
  can be successfully cast to a Python object when intercepting the
  allocating functions in this domain by the methods described in the
  Customize Memory Allocators section.

The default object allocator uses the pymalloc memory allocator.

Aviso:

  There must be an *attached thread state* when using these functions.

void *PyObject_Malloc(size_t n)
    * Parte da ABI Estável.*

   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)
    * Parte da ABI Estável desde a versão 3.7.*

   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.

   Adicionado na versão 3.5.

void *PyObject_Realloc(void *p, size_t n)
    * Parte da ABI Estável.*

   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)
    * Parte da ABI Estável.*

   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.

   Do not call this directly to free an object's memory; call the
   type's "tp_free" slot instead.

   Do not use this for memory allocated by "PyObject_GC_New" or
   "PyObject_GC_NewVar"; use "PyObject_GC_Del()" instead.

   Ver também:

     * "PyObject_GC_Del()" is the equivalent of this function for
       memory allocated by types that support garbage collection.

     * "PyObject_Malloc()"

     * "PyObject_Realloc()"

     * "PyObject_Calloc()"

     * "PyObject_New"

     * "PyObject_NewVar"

     * "PyType_GenericAlloc()"

     * "tp_free"


Alocadores de memória padrão
============================

Alocadores de memória padrão:

+---------------------------------+----------------------+--------------------+-----------------------+----------------------+
| Configuração                    | Nome                 | 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     |
+---------------------------------+----------------------+--------------------+-----------------------+----------------------+

Legenda:

* 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.

* "mimalloc": mimalloc memory allocator.  The pymalloc allocator will
  be used if mimalloc support isn't available.

* "+ debug": with debug hooks on the Python memory allocators.

* "Debug build": Python build in debug mode.


Alocadores de memória
=====================

Adicionado na versão 3.4.

type PyMemAllocatorEx

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

   +------------------------------------------------------------+-----------------------------------------+
   | Campo                                                      | Significado                             |
   |============================================================|=========================================|
   | "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                     |
   +------------------------------------------------------------+-----------------------------------------+

   Alterado na versão 3.5: The "PyMemAllocator" structure was renamed
   to "PyMemAllocatorEx" and a new "calloc" field was added.

type PyMemAllocatorDomain

   Enum used to identify an allocator domain. Domains:

   PYMEM_DOMAIN_RAW

      Funções:

      * "PyMem_RawMalloc()"

      * "PyMem_RawRealloc()"

      * "PyMem_RawCalloc()"

      * "PyMem_RawFree()"

   PYMEM_DOMAIN_MEM

      Funções:

      * "PyMem_Malloc()",

      * "PyMem_Realloc()"

      * "PyMem_Calloc()"

      * "PyMem_Free()"

   PYMEM_DOMAIN_OBJ

      Funções:

      * "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: a *thread state* is not *attached* when the allocator is
   called.

   For the remaining domains, the allocator must also be thread-safe:
   the allocator may be called in different interpreters that do not
   share a *GIL*.

   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.

   See also "PyPreConfig.allocator" and Preinitialize Python with
   PyPreConfig.

   Aviso:

     "PyMem_SetAllocator()" does have the following contract:

     * It can be called after "Py_PreInitialize()" and before
       "Py_InitializeFromConfig()" to install a custom memory
       allocator. There are no restrictions over the installed
       allocator other than the ones imposed by the domain (for
       instance, the Raw Domain allows the allocator to be called
       without an *attached thread state*). See the section on
       allocator domains for more information.

     * If called after Python has finish initializing (after
       "Py_InitializeFromConfig()" has been called) the allocator
       **must** wrap the existing allocator. Substituting the current
       allocator for some other arbitrary one is **not supported**.

   Alterado na versão 3.12: All allocators must be thread-safe.

void PyMem_SetupDebugHooks(void)

   Setup debug hooks in the Python memory allocators to detect memory
   errors.


Debug hooks on the Python memory allocators
===========================================

When Python is built in debug mode, the "PyMem_SetupDebugHooks()"
function is called at the Python preinitialization to setup debug
hooks on Python memory allocators to detect memory errors.

The "PYTHONMALLOC" environment variable can be used to install debug
hooks on a Python compiled in release mode (ex: "PYTHONMALLOC=debug").

The "PyMem_SetupDebugHooks()" function can be used to set debug hooks
after calling "PyMem_SetAllocator()".

These debug hooks fill dynamically allocated memory blocks with
special, recognizable bit patterns. Newly allocated memory is filled
with the byte "0xCD" ("PYMEM_CLEANBYTE"), freed memory is filled with
the byte "0xDD" ("PYMEM_DEADBYTE"). Memory blocks are surrounded by
"forbidden bytes" filled with the byte "0xFD" ("PYMEM_FORBIDDENBYTE").
Strings of these bytes are unlikely to be valid addresses, floats, or
ASCII strings.

Checagens em Tempo de Execução:

* Detect API violations. For example, detect if "PyObject_Free()" is
  called on a memory block 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 there is an *attached thread state* 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.

Let *S* = "sizeof(size_t)". "2*S" bytes are added at each end of each
block of *N* bytes requested.  The memory layout is like so, where p
represents the address returned by a malloc-like or realloc-like
function ("p[i:j]" means the slice of bytes from "*(p+i)" inclusive up
to "*(p+j)" exclusive; note that the treatment of negative indices
differs from a Python slice):

"p[-2*S:-S]"
   Number of bytes originally asked for.  This is a size_t, big-endian
   (easier to read in a memory dump).

"p[-S]"
   API identifier (ASCII character):

   * "'r'" for "PYMEM_DOMAIN_RAW".

   * "'m'" for "PYMEM_DOMAIN_MEM".

   * "'o'" for "PYMEM_DOMAIN_OBJ".

"p[-S+1:0]"
   Copies of PYMEM_FORBIDDENBYTE.  Used to catch under- writes and
   reads.

"p[0:N]"
   The requested memory, filled with copies of PYMEM_CLEANBYTE, used
   to catch reference to uninitialized memory.  When a realloc-like
   function is called requesting a larger memory block, the new excess
   bytes are also filled with PYMEM_CLEANBYTE.  When a free-like
   function is called, these are overwritten with PYMEM_DEADBYTE, to
   catch reference to freed memory.  When a realloc- like function is
   called requesting a smaller memory block, the excess old bytes are
   also filled with PYMEM_DEADBYTE.

"p[N:N+S]"
   Copies of PYMEM_FORBIDDENBYTE.  Used to catch over- writes and
   reads.

"p[N+S:N+2*S]"
   Only used if the "PYMEM_DEBUG_SERIALNO" macro is defined (not
   defined by default).

   A serial number, incremented by 1 on each call to a malloc-like or
   realloc-like function.  Big-endian "size_t".  If "bad memory" is
   detected later, the serial number gives an excellent way to set a
   breakpoint on the next run, to capture the instant at which this
   block was passed out.  The static function bumpserialno() in
   obmalloc.c is the only place the serial number is incremented, and
   exists so you can set such a breakpoint easily.

A realloc-like or free-like function first checks that the
PYMEM_FORBIDDENBYTE bytes at each end are intact.  If they've been
altered, diagnostic output is written to stderr, and the program is
aborted via Py_FatalError().  The other main failure mode is provoking
a memory error when a program reads up one of the special bit patterns
and tries to use it as an address.  If you get in a debugger then and
look at the object, you're likely to see that it's entirely filled
with PYMEM_DEADBYTE (meaning freed memory is getting used) or
PYMEM_CLEANBYTE (meaning uninitialized memory is getting used).

Alterado na versão 3.6: The "PyMem_SetupDebugHooks()" 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 there is an *attached
thread state* when functions of "PYMEM_DOMAIN_OBJ" and
"PYMEM_DOMAIN_MEM" domains are called.

Alterado na versão 3.8: Byte patterns "0xCB" ("PYMEM_CLEANBYTE"),
"0xDB" ("PYMEM_DEADBYTE") and "0xFB" ("PYMEM_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 either 256 KiB on 32-bit
platforms or 1 MiB on 64-bit platforms. 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()" e "free()" do contrário.

This allocator is disabled if Python is configured with the "--
without-pymalloc" option. It can also be disabled at runtime using the
"PYTHONMALLOC" environment variable (ex: "PYTHONMALLOC=malloc").

Typically, it makes sense to disable the pymalloc allocator when
building Python with AddressSanitizer ("--with-address-sanitizer")
which helps uncover low level bugs within the C code.


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

Adicionado na versão 3.4.

type PyObjectArenaAllocator

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

   +----------------------------------------------------+-----------------------------------------+
   | Campo                                              | Significado                             |
   |====================================================|=========================================|
   | "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.


The mimalloc allocator
======================

Adicionado na versão 3.13.

Python supports the mimalloc allocator when the underlying platform
support is available. mimalloc "is a general purpose allocator with
excellent performance characteristics. Initially developed by Daan
Leijen for the runtime systems of the Koka and Lean languages."


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

Adicionado na versão 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".


Exemplos
========

Here is the example from section Visão Geral, rewritten so that the
I/O buffer is allocated from the Python heap by using the first
function set:

   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;

The same code using the type-oriented function set:

   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_Free(buf); /* allocated with PyMem_New */
   return res;

Note that in the two examples above, the buffer is always manipulated
via functions belonging to the same set. Indeed, it is required to use
the same memory API family for a given memory block, so that the risk
of mixing different allocators is reduced to a minimum. The following
code sequence contains two errors, one of which is labeled as *fatal*
because it mixes two different allocators operating on different
heaps.

   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_Free()  */

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_Free()".

These will be explained in the next chapter on defining and
implementing new object types in C.
