Description

Memory slices provide a space-efficient and multi-processing scalable way to allocate equal-sized pieces of memory, just like the original GMemChunks (from GLib <= 2.8), while avoiding their excessive memory-waste, scalability and performance problems.

To achieve these goals, the slice allocator uses a sophisticated, layered design that has been inspired by Bonwick's slab allocator ^[5]. It uses posix_memalign() to optimize allocations of many equally-sized chunks, and has per-thread free lists (the so-called magazine layer) to quickly satisfy allocation requests of already known structure sizes. This is accompanied by extra caching logic to keep freed memory around for some time before returning it to the system. Memory that is unused due to alignment constraints is used for cache colorization (random distribution of chunk addresses) to improve CPU cache utilization. The caching layer of the slice allocator adapts itself to high lock contention to improve scalability.

The slice allocator can allocate blocks as small as two pointers, and unlike malloc(), it does not reserve extra space per block. For large block sizes, g_slice_new() and g_slice_alloc() will automatically delegate to the system malloc() implementation. For newly written code it is recommended to use the new g_slice API instead of g_malloc() and friends, as long as objects are not resized during their lifetime and the object size used at allocation time is still available when freeing.

  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]);
    }

  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);

Details

gpointer            g_slice_alloc                       (gsize block_size);

gpointer            g_slice_alloc0                      (gsize block_size);

void                g_slice_free1                       (gsize block_size,
                                                         gpointer mem_block);

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

#define             g_slice_new(type)

#define             g_slice_new0(type)

#define             g_slice_free(type, mem)

#define             g_slice_free_chain(type, mem_chain, next)