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PEP 445

This commit is contained in:
Victor Stinner 2013-06-18 21:04:34 +02:00
parent 69f972bb2b
commit 5cfe3ed35f
1 changed files with 151 additions and 85 deletions
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pep-0445.txt
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@ -46,53 +46,84 @@ API changes
- ``void* PyMem_RawMalloc(size_t size)``
- ``void* PyMem_RawRealloc(void *ptr, size_t new_size)``
- ``void PyMem_RawFree(void *ptr)``
- the behaviour of requesting zero bytes is not defined: return *NULL* or a
distinct non-*NULL* pointer depending on the platform.
* Add a new ``PyMemAllocators`` structure::
* Add a new ``PyMemBlockAllocator`` structure::
typedef struct {
/* user context passed as the first argument to the 3 functions */
void *ctx;
/* allocate memory */
/* allocate a memory block */
void* (*malloc) (void *ctx, size_t size);
/* allocate memory or resize a memory buffer */
/* allocate or resize a memory block */
void* (*realloc) (void *ctx, void *ptr, size_t new_size);
/* release memory */
/* release a memory block */
void (*free) (void *ctx, void *ptr);
} PyMemAllocators;
} PyMemBlockAllocator;
* Add new functions to get and set memory block allocators:
- ``void PyMem_GetRawAllocators(PyMemAllocators *allocators)``
- ``void PyMem_SetRawAllocators(PyMemAllocators *allocators)``
- ``void PyMem_GetAllocators(PyMemAllocators *allocators)``
- ``void PyMem_SetAllocators(PyMemAllocators *allocators)``
- ``void PyObject_GetAllocators(PyMemAllocators *allocators)``
- ``void PyObject_SetAllocators(PyMemAllocators *allocators)``
- Get/Set internal functions of ``PyMem_RawMalloc()``,
``PyMem_RawRealloc()`` and ``PyMem_RawFree()``:
* Add new functions to get and set memory mapping allocators:
* ``void PyMem_GetRawAllocator(PyMemBlockAllocator *allocator)``
* ``void PyMem_SetRawAllocator(PyMemBlockAllocator *allocator)``
- ``void _PyObject_GetArenaAllocators(void **ctx_p, void* (**malloc_p) (void *ctx, size_t size), void (**free_p) (void *ctx, void *ptr, size_t size))``
- ``void _PyObject_SetArenaAllocators(void *ctx, void* (*malloc) (void *ctx, size_t size), void (*free) (void *ctx, void *ptr, size_t size))``
- Get/Set internal functions of ``PyMem_Malloc()``,
``PyMem_Realloc()`` and ``PyMem_Free()``:
* ``void PyMem_GetAllocator(PyMemBlockAllocator *allocator)``
* ``void PyMem_SetAllocator(PyMemBlockAllocator *allocator)``
* ``malloc(ctx, 0)`` and ``realloc(ctx, ptr, 0)`` must not return *NULL*:
it would be treated as an error.
- Get/Set internal functions of ``PyObject_Malloc()``,,
``PyObject_Realloc()`` and ``PyObject_Free()``:
* ``void PyObject_GetAllocator(PyMemBlockAllocator *allocator)``
* ``void PyObject_SetAllocator(PyMemBlockAllocator *allocator)``
* Add a new ``PyMemMappingAllocator`` structure::
typedef struct {
/* user context passed as the first argument to the 2 functions */
void *ctx;
/* allocate a memory mapping */
void* (*malloc) (void *ctx, size_t size);
/* release a memory mapping */
void (*free) (void *ctx, void *ptr, size_t size);
} PyMemMappingAllocator;
* Add a new function to get and set memory mapping allocator:
- ``void PyMem_GetMappingAllocator(PyMemMappingAllocator *allocator)``
- ``void PyMem_SetMappingAllocator(PyMemMappingAllocator *allocator)``
- Currently, this allocator is only used internally by *pymalloc* to allocate
arenas.
* Add a new function to setup the builtin Python debug hooks when memory
allocators are replaced:
- ``void PyMem_SetupDebugHooks(void)``
.. note::
The builtin Python debug hooks were introduced in Python 2.3 and implement the
following checks:
The builtin Python debug hooks were introduced in Python 2.3 and implement the
following checks:
* Newly allocated memory is filled with the byte 0xCB, freed memory is filled
with the byte 0xDB.
* Detect API violations, ex: ``PyObject_Free()`` called on a memory block
* Newly allocated memory is filled with the byte ``0xCB``, freed memory is
filled with the byte ``0xDB``.
* Detect API violations, ex: ``PyObject_Free()`` 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)
* Detect write before the start of the buffer (buffer underflow)
* Detect write after the end of the buffer (buffer overflow)
The *pymalloc* allocator is used by default for:
``PyObject_Malloc()``, ``PyObject_Realloc()`` and ``PyObject_Free()``.
Make usage of these new APIs
@ -117,10 +148,10 @@ Make usage of these new APIs
Examples
========
Use case 1: Replace Memory Allocators, keep pymalloc
Use case 1: Replace Memory Allocator, keep pymalloc
----------------------------------------------------
Setup your custom memory allocators, keeping pymalloc. Dummy example wasting 2
Setup your custom memory allocator, keeping pymalloc. Dummy example wasting 2
bytes per allocation, and 10 bytes per arena::
#include <stdlib.h>
@ -156,30 +187,30 @@ bytes per allocation, and 10 bytes per arena::
free(ptr);
}
void setup_custom_allocators(void)
void setup_custom_allocator(void)
{
PyMemAllocators alloc;
PyMemBlockAllocator alloc;
alloc.ctx = &alloc_padding;
alloc.malloc = my_malloc;
alloc.realloc = my_realloc;
alloc.free = my_free;
PyMem_SetRawAllocators(&alloc);
PyMem_SetAllocators(&alloc);
PyMem_SetRawAllocator(&alloc);
PyMem_SetAllocator(&alloc);
_PyObject_SetArenaAllocators(&arena_padding,
_PyObject_SetArenaAllocator(&arena_padding,
my_alloc_arena, my_free_arena);
PyMem_SetupDebugHooks();
}
.. warning::
Remove the call ``PyMem_SetRawAllocators(&alloc)`` if the new allocators
Remove the call ``PyMem_SetRawAllocator(&alloc)`` if the new allocator
are not thread-safe.
Use case 2: Replace Memory Allocators, override pymalloc
Use case 2: Replace Memory Allocator, override pymalloc
--------------------------------------------------------
If your allocator is optimized for allocation of small objects (less than 512
@ -209,23 +240,23 @@ Dummy Example wasting 2 bytes per allocation::
free(ptr);
}
void setup_custom_allocators(void)
void setup_custom_allocator(void)
{
PyMemAllocators alloc;
PyMemBlockAllocator alloc;
alloc.ctx = &padding;
alloc.malloc = my_malloc;
alloc.realloc = my_realloc;
alloc.free = my_free;
PyMem_SetRawAllocators(&alloc);
PyMem_SetAllocators(&alloc);
PyObject_SetAllocators(&alloc);
PyMem_SetRawAllocator(&alloc);
PyMem_SetAllocator(&alloc);
PyObject_SetAllocator(&alloc);
PyMem_SetupDebugHooks();
}
.. warning::
Remove the call ``PyMem_SetRawAllocators(&alloc)`` if the new allocators
Remove the call ``PyMem_SetRawAllocator(&alloc)`` if the new allocator
are not thread-safe.
@ -236,15 +267,15 @@ Use case 3: Setup Allocator Hooks
Example to setup hooks on all memory allocators::
struct {
PyMemAllocators pymem;
PyMemAllocators pymem_raw;
PyMemAllocators pyobj;
PyMemBlockAllocator pymem;
PyMemBlockAllocator pymem_raw;
PyMemBlockAllocator pyobj;
/* ... */
} hook;
static void* hook_malloc(void *ctx, size_t size)
{
PyMemAllocators *alloc = (PyMemAllocators *)ctx;
PyMemBlockAllocator *alloc = (PyMemBlockAllocator *)ctx;
/* ... */
ptr = alloc->malloc(alloc->ctx, size);
/* ... */
@ -253,7 +284,7 @@ Example to setup hooks on all memory allocators::
static void* hook_realloc(void *ctx, void *ptr, size_t new_size)
{
PyMemAllocators *alloc = (PyMemAllocators *)ctx;
PyMemBlockAllocator *alloc = (PyMemBlockAllocator *)ctx;
void *ptr2;
/* ... */
ptr2 = alloc->realloc(alloc->ctx, ptr, new_size);
@ -263,7 +294,7 @@ Example to setup hooks on all memory allocators::
static void hook_free(void *ctx, void *ptr)
{
PyMemAllocators *alloc = (PyMemAllocators *)ctx;
PyMemBlockAllocator *alloc = (PyMemBlockAllocator *)ctx;
/* ... */
alloc->free(alloc->ctx, ptr);
/* ... */
@ -271,7 +302,7 @@ Example to setup hooks on all memory allocators::
void setup_hooks(void)
{
PyMemAllocators alloc;
PyMemBlockAllocator alloc;
static int installed = 0;
if (installed)
@ -282,21 +313,21 @@ Example to setup hooks on all memory allocators::
alloc.realloc = hook_realloc;
alloc.free = hook_free;
PyMem_GetRawAllocators(&hook.pymem_raw);
PyMem_GetRawAllocator(&hook.pymem_raw);
alloc.ctx = &hook.pymem_raw;
PyMem_SetRawAllocators(&alloc);
PyMem_SetRawAllocator(&alloc);
PyMem_GetAllocators(&hook.pymem);
PyMem_GetAllocator(&hook.pymem);
alloc.ctx = &hook.pymem;
PyMem_SetAllocators(&alloc);
PyMem_SetAllocator(&alloc);
PyObject_GetAllocators(&hook.pyobj);
PyObject_GetAllocator(&hook.pyobj);
alloc.ctx = &hook.pyobj;
PyObject_SetAllocators(&alloc);
PyObject_SetAllocator(&alloc);
}
.. warning::
Remove the call ``PyMem_SetRawAllocators(&alloc)`` if hooks are not
Remove the call ``PyMem_SetRawAllocator(&alloc)`` if hooks are not
thread-safe.
.. note::
@ -326,13 +357,19 @@ Only have one generic get/set function
Replace the 6 functions:
* ``PyMem_GetRawAllocators()``, ``PyMem_GetAllocators()``, ``PyObject_GetAllocators()``
* ``PyMem_SetRawAllocators(allocators)``, ``PyMem_SetAllocators(allocators)``, ``PyObject_SetAllocators(allocators)``
* ``PyMem_GetRawAllocator(PyMemBlockAllocator *allocator)``
* ``PyMem_GetAllocator(PyMemBlockAllocator *allocator)``
* ``PyObject_GetAllocator(PyMemBlockAllocator *allocator)``
* ``PyMem_SetRawAllocator(allocator)``
* ``PyMem_SetAllocator(PyMemBlockAllocator *allocator)``
* ``PyObject_SetAllocator(PyMemBlockAllocator *allocator)``
with 2 functions with an additional *domain* argument:
* ``Py_GetAllocators(domain)``
* ``Py_SetAllocators(domain, allocators)``
* ``int Py_GetAllocator(int domain, PyMemBlockAllocator *allocator)``
* ``int Py_SetAllocator(int domain, PyMemBlockAllocator *allocator)``
These functions return 0 on success, or -1 if the domain is unknown.
where domain is one of these values:
@ -341,9 +378,19 @@ where domain is one of these values:
* ``PYALLOC_PYOBJECT``
``_PyObject_GetArenaAllocators()`` and ``_PyObject_SetArenaAllocators()`` are
not merged and kept private because their prototypes are different and they are
specific to pymalloc.
PyMem_Malloc() reuses PyMem_RawMalloc() by default
--------------------------------------------------
``PyMem_Malloc()`` should call ``PyMem_RawMalloc()`` by default. So calling
``PyMem_SetRawAllocator()`` would also also patch ``PyMem_Malloc()``
indirectly.
Such change is less optimal, it adds another level of indirection.
In the proposed implementation of this PEP (issue #3329), ``PyMem_RawMalloc()``
calls directly ``malloc()``, whereas ``PyMem_Malloc()`` returns ``NULL`` if
size is larger than ``PY_SSIZE_T_MAX``, and the default allocator of
``PyMem_Malloc()`` calls ``malloc(1)`` if the size is zero.
Add a new PYDEBUGMALLOC environment variable
@ -353,8 +400,8 @@ To be able to use the Python builtin debug hooks even when a custom memory
allocator replaces the default Python allocator, an environment variable
``PYDEBUGMALLOC`` can be added to setup these debug function hooks, instead of
adding the new function ``PyMem_SetupDebugHooks()``. If the environment
variable is present, ``PyMem_SetRawAllocators()``, ``PyMem_SetAllocators()``
and ``PyObject_SetAllocators()`` will reinstall automatically the hook on top
variable is present, ``PyMem_SetRawAllocator()``, ``PyMem_SetAllocator()``
and ``PyObject_SetAllocator()`` will reinstall automatically the hook on top
of the new allocator.
An new environment variable would make the Python initialization even more
@ -386,21 +433,6 @@ objects of differenet types would have the same allocation location. Such
changes add too much complexity for a little gain.
No context argument
-------------------
Simplify the signature of allocator functions, remove the context argument:
* ``void* malloc(size_t size)``
* ``void* realloc(void *ptr, size_t new_size)``
* ``void free(void *ptr)``
It is likely for an allocator hook to be reused for ``PyMem_SetAllocators()``
and ``PyObject_SetAllocators()``, but the hook must call a different function
depending on the allocator. The context is a convenient way to reuse the same
allocator or hook for different APIs.
PyMem_Malloc() GIL-free
-----------------------
@ -436,7 +468,6 @@ be seen. Remaining ``malloc()`` may allocate a lot of memory and so would be
missed in reports.
Use existing debug tools to analyze the memory
----------------------------------------------
@ -458,6 +489,36 @@ information. Being able to setup a hook on allocators called with the GIL held
allow to read a lot of useful data from Python internals.
Add msize()
-----------
Add another field to ``PyMemBlockAllocator`` and ``PyMemMappingAllocator``::
size_t msize(void *ptr);
This function returns the size of a memory block or a memory mapping. Return
(size_t)-1 if the function is not implemented or if the pointer is unknown
(ex: NULL pointer).
On Windows, this function can be implemented using ``_msize()`` and
``VirtualQuery()``.
No context argument
-------------------
Simplify the signature of allocator functions, remove the context argument:
* ``void* malloc(size_t size)``
* ``void* realloc(void *ptr, size_t new_size)``
* ``void free(void *ptr)``
It is likely for an allocator hook to be reused for ``PyMem_SetAllocator()``
and ``PyObject_SetAllocator()``, but the hook must call a different function
depending on the allocator. The context is a convenient way to reuse the same
allocator or hook for different APIs.
External libraries
==================
@ -476,7 +537,6 @@ See also the `GNU libc: Memory Allocation Hooks
<http://www.gnu.org/software/libc/manual/html_node/Hooks-for-Malloc.html>`_.
Memory allocators
=================
@ -490,18 +550,24 @@ tcmalloc which is part of `gperftools <http://code.google.com/p/gperftools/>`_.
mappings are usually used for large allocations (ex: larger than 256 KB),
whereas the heap is used for small allocations.
The heap is handled by ``brk()`` and ``sbrk()`` system calls on Linux, and is
contiguous. Memory mappings are handled by ``mmap()`` on UNIX and
On UNIX, the heap is handled by ``brk()`` and ``sbrk()`` system calls on Linux,
and it is contiguous. On Windows, the heap is handled by ``HeapAlloc()`` and
may be discontiguous. Memory mappings are handled by ``mmap()`` on UNIX and
``VirtualAlloc()`` on Windows, they may be discontiguous.
Releasing a memory mapping gives back immediatly the memory to the system. For
the heap, memory is only given back to the system if it is at the end of the
heap. Otherwise, the memory will only be given back to the system when all the
memory located after the released memory are also released. To allocate memory
in the heap, the allocator tries to reuse free space. If there is no contiguous
space big enough, the heap must be increased, even if we have more free space
than required size. This issue is called the "memory fragmentation": the
memory usage seen by the system may be much higher than real usage.
memory located after the released memory are also released.
To allocate memory in the heap, the allocator tries to reuse free space. If
there is no contiguous space big enough, the heap must be increased, even if we
have more free space than required size. This issue is called the "memory
fragmentation": the memory usage seen by the system may be much higher than
real usage.
On Windows, ``HeapAlloc()`` creates a new memory mapping with
``VirtualAlloc()`` if there is not enough free contiguous memory.
CPython has a pymalloc allocator using arenas of 256 KB for allocations smaller
than 512 bytes. This allocator is optimized for small objects with a short