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Diffstat (limited to 'Doc/c-api/memory.rst')
| -rw-r--r-- | Doc/c-api/memory.rst | 113 |
1 files changed, 77 insertions, 36 deletions
diff --git a/Doc/c-api/memory.rst b/Doc/c-api/memory.rst index 290ef09dce..3ff545275f 100644 --- a/Doc/c-api/memory.rst +++ b/Doc/c-api/memory.rst @@ -85,9 +85,12 @@ for the I/O buffer escapes completely the Python memory manager. .. seealso:: + The :envvar:`PYTHONMALLOC` environment variable can be used to configure + the memory allocators used by Python. + The :envvar:`PYTHONMALLOCSTATS` environment variable can be used to print - memory allocation statistics every time a new object arena is created, and - on shutdown. + statistics of the :ref:`pymalloc memory allocator <pymalloc>` every time a + new pymalloc object arena is created, and on shutdown. Raw Memory Interface @@ -162,15 +165,17 @@ 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 block allocator uses the following functions: -:c:func:`malloc`, :c:func:`calloc`, :c:func:`realloc` and :c:func:`free`; call -``malloc(1)`` (or ``calloc(1, 1)``) when requesting zero bytes. +By default, these functions use :ref:`pymalloc memory allocator <pymalloc>`. .. warning:: The :term:`GIL <global interpreter lock>` must be held when using these functions. +.. versionchanged:: 3.6 + + The default allocator is now pymalloc instead of system :c:func:`malloc`. + .. c:function:: void* PyMem_Malloc(size_t n) Allocates *n* bytes and returns a pointer of type :c:type:`void\*` to the @@ -292,15 +297,32 @@ Customize Memory Allocators Enum used to identify an allocator domain. Domains: - * :c:data:`PYMEM_DOMAIN_RAW`: functions :c:func:`PyMem_RawMalloc`, - :c:func:`PyMem_RawRealloc`, :c:func:`PyMem_RawCalloc` and - :c:func:`PyMem_RawFree` - * :c:data:`PYMEM_DOMAIN_MEM`: functions :c:func:`PyMem_Malloc`, - :c:func:`PyMem_Realloc`, :c:func:`PyMem_Calloc` and :c:func:`PyMem_Free` - * :c:data:`PYMEM_DOMAIN_OBJ`: functions :c:func:`PyObject_Malloc`, - :c:func:`PyObject_Realloc`, :c:func:`PyObject_Calloc` and - :c:func:`PyObject_Free` + .. c:var:: PYMEM_DOMAIN_RAW + + Functions: + + * :c:func:`PyMem_RawMalloc` + * :c:func:`PyMem_RawRealloc` + * :c:func:`PyMem_RawCalloc` + * :c:func:`PyMem_RawFree` + + .. c:var:: PYMEM_DOMAIN_MEM + + Functions: + + * :c:func:`PyMem_Malloc`, + * :c:func:`PyMem_Realloc` + * :c:func:`PyMem_Calloc` + * :c:func:`PyMem_Free` + .. c:var:: PYMEM_DOMAIN_OBJ + + Functions: + + * :c:func:`PyObject_Malloc` + * :c:func:`PyObject_Realloc` + * :c:func:`PyObject_Calloc` + * :c:func:`PyObject_Free` .. c:function:: void PyMem_GetAllocator(PyMemAllocatorDomain domain, PyMemAllocatorEx *allocator) @@ -325,43 +347,62 @@ Customize Memory Allocators .. c:function:: void PyMem_SetupDebugHooks(void) - Setup hooks to detect bugs in the following Python memory allocator - functions: - - - :c:func:`PyMem_RawMalloc`, :c:func:`PyMem_RawRealloc`, - :c:func:`PyMem_RawCalloc`, :c:func:`PyMem_RawFree` - - :c:func:`PyMem_Malloc`, :c:func:`PyMem_Realloc`, :c:func:`PyMem_Calloc`, - :c:func:`PyMem_Free` - - :c:func:`PyObject_Malloc`, :c:func:`PyObject_Realloc`, - :c:func:`PyObject_Calloc`, :c:func:`PyObject_Free` + Setup hooks to detect bugs in the Python memory allocator functions. Newly allocated memory is filled with the byte ``0xCB``, freed memory is - filled with the byte ``0xDB``. Additional checks: + filled with the byte ``0xDB``. - - detect API violations, ex: :c:func:`PyObject_Free` called on a buffer + Runtime checks: + + - Detect API violations, ex: :c:func:`PyObject_Free` called on a buffer allocated by :c:func:`PyMem_Malloc` - - detect write before the start of the buffer (buffer underflow) - - detect write after the end of the buffer (buffer overflow) + - Detect write before the start of the buffer (buffer underflow) + - Detect write after the end of the buffer (buffer overflow) + - Check that the :term:`GIL <global interpreter lock>` is held when + allocator functions of :c:data:`PYMEM_DOMAIN_OBJ` (ex: + :c:func:`PyObject_Malloc`) and :c:data:`PYMEM_DOMAIN_MEM` (ex: + :c:func:`PyMem_Malloc`) domains are called + + On error, the debug hooks use the :mod:`tracemalloc` module to get the + traceback where a memory block was allocated. The traceback is only + displayed if :mod:`tracemalloc` is tracing Python memory allocations and the + memory block was traced. - The function does nothing if Python is not compiled is debug mode. + These hooks are installed by default if Python is compiled in debug + mode. The :envvar:`PYTHONMALLOC` environment variable can be used to install + debug hooks on a Python compiled in release mode. + .. versionchanged:: 3.6 + This function now also works on Python compiled in release mode. + On error, the debug hooks now use :mod:`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 :c:data:`PYMEM_DOMAIN_OBJ` and + :c:data:`PYMEM_DOMAIN_MEM` domains are called. -Customize PyObject Arena Allocator -================================== -Python has a *pymalloc* allocator for allocations smaller than 512 bytes. This -allocator is optimized for small objects with a short lifetime. It uses memory -mappings called "arenas" with a fixed size of 256 KB. It falls back to -:c:func:`PyMem_RawMalloc` and :c:func:`PyMem_RawRealloc` for allocations larger -than 512 bytes. *pymalloc* is the default allocator used by -:c:func:`PyObject_Malloc`. +.. _pymalloc: -The default arena allocator uses the following functions: +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 KB. It falls back to :c:func:`PyMem_RawMalloc` and +:c:func:`PyMem_RawRealloc` for allocations larger than 512 bytes. + +*pymalloc* is the default allocator of the :c:data:`PYMEM_DOMAIN_MEM` (ex: +:c:func:`PyObject_Malloc`) and :c:data:`PYMEM_DOMAIN_OBJ` (ex: +:c:func:`PyObject_Malloc`) domains. + +The arena allocator uses the following functions: * :c:func:`VirtualAlloc` and :c:func:`VirtualFree` on Windows, * :c:func:`mmap` and :c:func:`munmap` if available, * :c:func:`malloc` and :c:func:`free` otherwise. +Customize pymalloc Arena Allocator +---------------------------------- + .. versionadded:: 3.4 .. c:type:: PyObjectArenaAllocator |