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GLib Reference Manual | |
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#include <glib.h> gpointer g_slice_alloc (gsize block_size); gpointer g_slice_alloc0 (gsize block_size); gpointer g_slice_copy (gsize block_size,gconstpointer mem_block); 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_dup (type, mem) #define g_slice_free (type, mem) #define g_slice_free_chain (type, mem_chain, next)
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
[1].
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.
Example 8. Using the slice allocator
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 |
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]); } |
Example 9. 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); |
gpointer g_slice_alloc (gsize block_size);
Allocates a block of memory from the slice allocator.
The block adress handed out can be expected to be aligned
to at least 1 * sizeof (void*),
though in general slices are 2 * sizeof (void*) bytes aligned,
if a malloc() fallback implementation is used instead,
the alignment may be reduced in a libc dependent fashion.
Note that the underlying slice allocation mechanism can
be changed with the G_SLICE=always-malloc
environment variable.
|
the number of bytes to allocate |
Returns : |
a pointer to the allocated memory block |
Since 2.10
gpointer g_slice_alloc0 (gsize block_size);
Allocates a block of memory via g_slice_alloc() and initializes
the returned memory to 0. Note that the underlying slice allocation
mechanism can be changed with the
G_SLICE=always-malloc
environment variable.
|
the number of bytes to allocate |
Returns : |
a pointer to the allocated block |
Since 2.10
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.
|
the number of bytes to allocate |
|
the memory to copy |
Returns : |
a pointer to the allocated memory block |
Since 2.14
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, also see G_SLICE for
related debugging options.
|
the size of the block |
|
a pointer to the block to free |
Since 2.10
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, also see G_SLICE for
related debugging options.
|
the size of the blocks |
|
a pointer to the first block of the chain |
|
the offset of the next field in the blocks |
Since 2.10
#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 (
and casts the returned pointer to a pointer of the given type,
avoiding a type cast in the source code.
Note that the underlying slice allocation mechanism can
be changed with the G_SLICE=always-malloc
environment variable.
type)
|
the type to allocate, typically a structure name |
Returns : |
a pointer to the allocated block, cast to a pointer to type
|
Since 2.10
#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 (
and casts the returned pointer to a pointer of the given type,
avoiding a type cast in the source code.
Note that the underlying slice allocation mechanism can
be changed with the G_SLICE=always-malloc
environment variable.
type)
|
the type to allocate, typically a structure name |
Since 2.10
#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 (
and casts the returned pointer to a pointer of the given type,
avoiding a type cast in the source code.
Note that the underlying slice allocation mechanism can
be changed with the G_SLICE=always-malloc
environment variable.
type)
|
the type to duplicate, typically a structure name |
|
the memory to copy into the allocated block |
Returns : |
a pointer to the allocated block, cast to a pointer to type
|
Since 2.14
#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, also see G_SLICE for
related debugging options.
|
the type of the block to free, typically a structure name |
|
a pointer to the block to free |
Since 2.10
#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, also see G_SLICE for
related debugging options.
|
the type of the mem_chain blocks |
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a pointer to the first block of the chain |
|
the field name of the next pointer in type
|
Since 2.10
[1] [Bonwick94] Jeff Bonwick, The slab allocator: An object-caching kernel memory allocator. USENIX 1994, and [Bonwick01] Bonwick and Jonathan Adams, Magazines and vmem: Extending the slab allocator to many cpu's and arbitrary resources. USENIX 2001