Memory Slices: GLib Reference Manual

## Memory Slices Memory Slices — efficient way to allocate groups of equal-sized chunks of memory |

## Functions

gpointer | g_slice_alloc ()
gpointer | g_slice_alloc0 ()
gpointer | g_slice_copy ()
void | g_slice_free1 ()
void | g_slice_free_chain_with_offset ()
#define | g_slice_new()
#define | g_slice_new0()
#define | g_slice_dup()
#define | g_slice_free()
#define | g_slice_free_chain()

## Includes

    #include <gmodule.h>

## Description

GSlice was a space-efficient and multi-processing scalable way to allocate equal sized pieces of memory. Since GLib 2.76, its implementation has been removed and it calls `g_malloc()` and `g_free_sized()`, because the performance of the system-default allocators has improved on all platforms since GSlice was written.

The GSlice APIs have not been deprecated, as they are widely in use and doing so would be very disruptive for little benefit.

New code should be written using `g_new()`/`g_malloc()` and `g_free_sized()` or `g_free()`. There is no particular benefit in porting existing code away from `g_slice_new()`/`g_slice_free()` unless it’s being rewritten anyway.

Here is an example for using the slice allocator:

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    gchar *mem[10000];
    gint i;

    // Allocate 10000 blocks.
    for (i = 0; i < 10000; i++)
      {
        mem[i] = g_slice_alloc (50);

        // Fill in the memory with some junk.
        for (j = 0; j < 50; j++)
          mem[i][j] = i * j;
      }

    // Now free all of the blocks.
    for (i = 0; i < 10000; i++)
      g_slice_free1 (50, mem[i]);

And here is an example for using the using the slice allocator with data structures:

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    GRealArray *array;

    // Allocate one block, using the g_slice_new() macro.
    array = g_slice_new (GRealArray);

    // We can now use array just like a normal pointer to a structure.
    array->data            = NULL;
    array->len             = 0;
    array->alloc           = 0;
    array->zero_terminated = (zero_terminated ? 1 : 0);
    array->clear           = (clear ? 1 : 0);
    array->elt_size        = elt_size;

    // We can free the block, so it can be reused.
    g_slice_free (GRealArray, array);

## Functions

### g_slice_alloc ()

    gpointer
    g_slice_alloc (gsize block_size);

Allocates a block of memory from the libc allocator.

The block address handed out can be expected to be aligned to at least `1 * sizeof (void*)`.

Since GLib 2.76 this always uses the system `malloc()` implementation internally.

#### Parameters

block_size | the number of bytes to allocate |

#### Returns

a pointer to the allocated memory block, which will be `NULL` if and only if `mem_size` is 0.

[nullable]

Since: 2.10

### g_slice_alloc0 ()

    gpointer
    g_slice_alloc0 (gsize block_size);

Allocates a block of memory via `g_slice_alloc()` and initializes the returned memory to 0.

Since GLib 2.76 this always uses the system `malloc()` implementation internally.

#### Parameters

block_size | the number of bytes to allocate |

#### Returns

a pointer to the allocated block, which will be `NULL` if and only if `mem_size` is 0.

[nullable]

Since: 2.10

### g_slice_copy ()

    gpointer
    g_slice_copy (gsize block_size,
                  gconstpointer mem_block);

Allocates a block of memory from the slice allocator and copies `block_size` bytes into it from `mem_block` .

`mem_block` must be non-`NULL` if `block_size` is non-zero.

Since GLib 2.76 this always uses the system `malloc()` implementation internally.

#### Parameters

block_size | the number of bytes to allocate |
mem_block | the memory to copy |

#### Returns

a pointer to the allocated memory block, which will be `NULL` if and only if `mem_size` is 0.

[nullable]

Since: 2.14

### g_slice_free1 ()

    void
    g_slice_free1 (gsize block_size,
                   gpointer mem_block);

Frees a block of memory.

The memory must have been allocated via `g_slice_alloc()` or `g_slice_alloc0()` and the `block_size` has to match the size specified upon allocation. Note that the exact release behaviour can be changed with the `G_DEBUG=gc-friendly` environment variable.

If `mem_block` is `NULL`, this function does nothing.

Since GLib 2.76 this always uses the system `free_sized()` implementation internally.

#### Parameters

block_size | the size of the block |
mem_block | a pointer to the block to free. | [nullable]

Since: 2.10

### g_slice_free_chain_with_offset ()

    void
    g_slice_free_chain_with_offset (gsize block_size,
                                    gpointer mem_chain,
                                    gsize next_offset);

Frees a linked list of memory blocks of structure type `type` .

The memory blocks must be equal-sized, allocated via `g_slice_alloc()` or `g_slice_alloc0()` and linked together by a `next` pointer (similar to GSList). The offset of the `next` field in each block is passed as third argument. Note that the exact release behaviour can be changed with the `G_DEBUG=gc-friendly` environment variable.

If `mem_chain` is `NULL`, this function does nothing.

Since GLib 2.76 this always uses the system `free_sized()` implementation internally.

#### Parameters

block_size | the size of the blocks |
mem_chain | a pointer to the first block of the chain. | [nullable]
next_offset | the offset of the `next` field in the blocks |

Since: 2.10

### g_slice_new()

    #define             g_slice_new(type)

A convenience macro to allocate a block of memory from the slice allocator.

It calls `g_slice_alloc()` with `sizeof (@type)` and casts the returned pointer to a pointer of the given type, avoiding a type cast in the source code.

This can never return `NULL` as the minimum allocation size from `sizeof (@type)` is 1 byte.

Since GLib 2.76 this always uses the system `malloc()` implementation internally.

#### Parameters

type | the type to allocate, typically a structure name |

#### Returns

a pointer to the allocated block, cast to a pointer to `type` .

[not nullable]

Since: 2.10

### g_slice_new0()

    #define             g_slice_new0(type)

A convenience macro to allocate a block of memory from the slice allocator and set the memory to 0.

It calls `g_slice_alloc0()` with `sizeof (@type)` and casts the returned pointer to a pointer of the given type, avoiding a type cast in the source code.

This can never return `NULL` as the minimum allocation size from `sizeof (@type)` is 1 byte.

Since GLib 2.76 this always uses the system `malloc()` implementation internally.

#### Parameters

type | the type to allocate, typically a structure name |

#### Returns

a pointer to the allocated block, cast to a pointer to `type` .

[not nullable]

Since: 2.10

### g_slice_dup()

    #define             g_slice_dup(type, mem)

A convenience macro to duplicate a block of memory using the slice allocator.

It calls `g_slice_copy()` with `sizeof (@type)` and casts the returned pointer to a pointer of the given type, avoiding a type cast in the source code.

This can never return `NULL`.

Since GLib 2.76 this always uses the system `malloc()` implementation internally.

#### Parameters

type | the type to duplicate, typically a structure name |
mem | the memory to copy into the allocated block. | [not nullable]

#### Returns

a pointer to the allocated block, cast to a pointer to `type` .

[not nullable]

Since: 2.14

### g_slice_free()

    #define             g_slice_free(type, mem)

A convenience macro to free a block of memory that has been allocated from the slice allocator.

It calls `g_slice_free1()` using `sizeof (type)` as the block size. Note that the exact release behaviour can be changed with the `G_DEBUG=gc-friendly` environment variable.

If `mem` is `NULL`, this macro does nothing.

Since GLib 2.76 this always uses the system `free()` implementation internally.

#### Parameters

type | the type of the block to free, typically a structure name |
mem | a pointer to the block to free. | [nullable]

Since: 2.10

### g_slice_free_chain()

    #define             g_slice_free_chain(type, mem_chain, next)

Frees a linked list of memory blocks of structure type `type` .

The memory blocks must be equal-sized, allocated via `g_slice_alloc()` or `g_slice_alloc0()` and linked together by a `next` pointer (similar to GSList). The name of the `next` field in `type` is passed as third argument. Note that the exact release behaviour can be changed with the `G_DEBUG=gc-friendly` environment variable.

If `mem_chain` is `NULL`, this function does nothing.

Since GLib 2.76 this always uses the system `free()` implementation internally.

#### Parameters

type | the type of the `mem_chain` blocks |
mem_chain | a pointer to the first block of the chain. | [nullable]
next | the field name of the next pointer in `type` |

Since: 2.10