mirror of
git://git.sv.gnu.org/emacs.git
synced 2026-04-30 10:11:47 -07:00
6907a9287c
Move most of the deprecated material to a new chapter of the manual (to avoid clutter and confusion) and ensure that each deprecated symbol has a recommendation for what to do instead. Copied from Perforce Change: 187471 ServerID: perforce.ravenbrook.com
106 lines
3.2 KiB
ReStructuredText
106 lines
3.2 KiB
ReStructuredText
.. index::
|
|
single: MFS
|
|
single: pool class; MFS
|
|
|
|
.. _pool-mfs:
|
|
|
|
MFS (Manual Fixed Small)
|
|
========================
|
|
|
|
**MFS** is an :term:`manually managed <manual memory management>`
|
|
:term:`pool class` for small objects of fixed size.
|
|
|
|
Unlike other manual pool classes, it is not subject to :term:`internal
|
|
fragmentation`: if the population remains bounded, the memory usage
|
|
remains bounded too. On the other hand, unlike :ref:`pool-mvt` and
|
|
:ref:`pool-mvff` it does not return unused memory to the arena for
|
|
reuse by other pools.
|
|
|
|
The implementation is very simple: unlike most other :term:`pool
|
|
classes` which store their control structures separately from the
|
|
allocated blocks, MFS maintains a stack of free blocks using a pointer
|
|
in the free block. :c:func:`mps_alloc` pops this stack and
|
|
:c:func:`mps_free` pushes it.
|
|
|
|
|
|
.. index::
|
|
single: MFS; properties
|
|
|
|
MFS properties
|
|
--------------
|
|
|
|
* Supports allocation via :c:func:`mps_alloc` and deallocation via
|
|
:c:func:`mps_free`.
|
|
|
|
* Does not support allocation via :term:`allocation points`.
|
|
|
|
* Does not support :term:`allocation frames`.
|
|
|
|
* Supports :term:`segregated allocation caches` (but using one would
|
|
be pointless, since all blocks are the same size).
|
|
|
|
* There are no garbage collections in this pool.
|
|
|
|
* Blocks may not contain :term:`references` to blocks in automatically
|
|
managed pools (unless these are registered as :term:`roots`).
|
|
|
|
* Allocations are fixed in size.
|
|
|
|
* The :term:`alignment` of blocks is not configurable: it is the
|
|
:term:`natural alignment` of the platform (see
|
|
:c:macro:`MPS_PF_ALIGN`).
|
|
|
|
* Blocks do not have :term:`dependent objects`.
|
|
|
|
* Blocks are not automatically :term:`reclaimed`.
|
|
|
|
* Blocks are not :term:`scanned <scan>`.
|
|
|
|
* Blocks are not protected by :term:`barriers (1)`.
|
|
|
|
* Blocks do not :term:`move <moving garbage collector>`.
|
|
|
|
* Blocks may not be registered for :term:`finalization`.
|
|
|
|
* Blocks must not belong to an :term:`object format`.
|
|
|
|
|
|
.. index::
|
|
single: MFS; interface
|
|
|
|
MFS interface
|
|
-------------
|
|
|
|
::
|
|
|
|
#include "mpscmfs.h"
|
|
|
|
.. c:function:: mps_pool_class_t mps_class_mfs(void)
|
|
|
|
Return the :term:`pool class` for an MFS (Manual Fixed Small)
|
|
:term:`pool`.
|
|
|
|
When creating an MFS pool, :c:func:`mps_pool_create_k` requires
|
|
one :term:`keyword argument`:
|
|
|
|
* :c:macro:`MPS_KEY_MFS_UNIT_SIZE` (type :c:type:`size_t`) is the
|
|
:term:`size` of blocks that will be allocated from this pool, in
|
|
:term:`bytes (1)`. It must be at least one :term:`word`.
|
|
|
|
In addition, :c:func:`mps_pool_create_k` accepts one optional
|
|
keyword argument:
|
|
|
|
* :c:macro:`MPS_KEY_EXTEND_BY` (type :c:type:`size_t`,
|
|
default 65536) is the :term:`size` of block that the pool will
|
|
request from the :term:`arena`. It must be at least as big as
|
|
the unit size specified by the :c:macro:`MPS_KEY_MFS_UNIT_SIZE`
|
|
keyword argument. If this is not a multiple of the unit size,
|
|
there will be wasted space in each block.
|
|
|
|
For example::
|
|
|
|
MPS_ARGS_BEGIN(args) {
|
|
MPS_ARGS_ADD(args, MPS_KEY_MFS_UNIT_SIZE, 1024);
|
|
MPS_ARGS_ADD(args, MPS_KEY_EXTEND_BY, 1024 * 1024);
|
|
res = mps_pool_create_k(&pool, arena, mps_class_mfs(), args);
|
|
} MPS_ARGS_END(args);
|