Memory Slices

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

Functions

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:

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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:

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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