10. MV (Manual Variable)

Deprecated

starting with version 1.111.

MVFF (Manual Variable First Fit) should be used instead.

MV is a general-purpose manually managed pool class that manages blocks of variable size.

10.1. MV properties

• Supports allocation via mps_alloc() and deallocation via mps_free().
• Does not support allocation via allocation points.
• Does not support allocation frames.
• Supports segregated allocation caches.
• There are no garbage collections in this pool.
• Blocks may not contain references to blocks in automatically managed pools (unless these are registered as roots).
• Allocations may be variable in size.
• The alignment of blocks is not configurable: it is the natural alignment of the platform (see MPS_PF_ALIGN).
• Blocks do not have dependent objects.
• Blocks are not automatically reclaimed.
• Blocks are not scanned.
• Blocks are not protected by barriers⁽¹⁾.
• Blocks do not move.
• Blocks may not be registered for finalization.
• Blocks must not belong to an object format.

10.2. MV interface

#include "mpscmv.h"

mps_class_t mps_class_mv(void)

Return the pool class for an MV (Manual Variable) pool.

When creating an MV pool, mps_pool_create_k() may take three keyword arguments:

• MPS_KEY_EXTEND_BY (type size_t, default 4096) is the size of segment that the pool will request from the arena.
• MPS_KEY_MEAN_SIZE (type size_t, default 32) is the predicted mean size of blocks that will be allocated from the pool.
• MPS_KEY_MAX_SIZE (type size_t, default 65536) is the predicted maximum size of blocks that will be allocated from the pool.

The mean and maximum sizes are hints to the MPS: the pool will be less efficient if these are wrong, but nothing will break.

For example:

MPS_ARGS_BEGIN(args) {
    MPS_ARGS_ADD(ARGS, MPS_KEY_MEAN_SIZE, 32);
    MPS_ARGS_ADD(ARGS, MPS_KEY_MAX_SIZE, 1024);
    MPS_ARGS_ADD(ARGS, MPS_KEY_EXTEND_BY, 1024 * 1024);
    MPS_ARGS_DONE(args);
    res = mps_pool_create_k(&pool, arena, mps_class_mfs(), args);
} MPS_ARGS_END(args);

Deprecated

starting with version 1.112.

When using mps_pool_create(), pass the segment size, mean size, and maximum size like this:

mps_res_t mps_pool_create(mps_pool_t *pool_o, mps_arena_t arena,
                          mps_class_t mps_class_mv(),
                          mps_size_t extend_size,
                          mps_size_t average_size,
                          mps_size_t maximum_size)

mps_class_t mps_class_mv_debug(void)

A debugging version of the MV pool class.

When creating a debugging MV pool, mps_pool_create_k() requires four keyword arguments: MPS_KEY_EXTEND_SIZE, MPS_KEY_MEAN_SIZE, MPS_KEY_MAX_SIZE are as described above, and MPS_KEY_POOL_DEBUG_OPTIONS specifies the debugging options. See mps_debug_option_s.

Deprecated

starting with version 1.112.

When using mps_pool_create(), pass the debugging options, segment size, mean size, and maximum size like this:

mps_res_t mps_pool_create(mps_pool_t *pool_o, mps_arena_t arena,
                          mps_class_t mps_class_mv_debug(),
                          mps_debug_option_s debug_option,
                          mps_size_t extend_size,
                          mps_size_t average_size,
                          mps_size_t maximum_size)

10.3. MV introspection

#include "mpscmv.h"

size_t mps_mv_free_size(mps_pool_t pool)

Return the total amount of free space in an MV pool.

pool is the MV pool.

Returns the total free space in the pool, in bytes⁽¹⁾.

size_t mps_mv_size(mps_pool_t pool)

Return the total size of an MV pool.

pool is the MV pool.

Returns the total size of the pool, in bytes⁽¹⁾. This is the sum of allocated space and free space.