glib.MemorySlice.MemorySlice Class Reference

List of all members.

Detailed Description

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. Example1.Using the slice allocator 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]); } Example2.Using the slice allocator with data structures 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);


Static Public Member Functions

static void * alloc (uint blockSize)
 Allocates a block of memory from the slice allocator.
static void * alloc0 (uint blockSize)
 Allocates a block of memory via g_slice_alloc() and initialize the returned memory to 0.
static void free1 (uint blockSize, void *memBlock)
 Frees a block of memory.
static void freeChainWithOffset (uint blockSize, void *memChain, uint nextOffset)
 Frees a linked list of memory blocks of structure type type.


Member Function Documentation

static void* glib.MemorySlice.MemorySlice.alloc ( uint  blockSize  )  [static]

Allocates a block of memory from the slice allocator.

The block adress handed out is guaranteed to be aligned to at least 2 * sizeof (void*). Note that the underlying slice allocation mechanism can be changed with the G_SLICE=always-malloc environment variable. block_size: the number of bytes to allocate Returns: a pointer to the allocated memory block Since 2.10

static void* glib.MemorySlice.MemorySlice.alloc0 ( uint  blockSize  )  [static]

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

Note that the underlying slice allocation mechanism can be changed with the G_SLICE=always-malloc environment variable. block_size: the number of bytes to allocate Returns: a pointer to the allocated block Since 2.10

static void glib.MemorySlice.MemorySlice.free1 ( uint  blockSize,
void *  memBlock 
) [static]

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. block_size: the size of the block mem_block: a pointer to the block to free Since 2.10

static void glib.MemorySlice.MemorySlice.freeChainWithOffset ( uint  blockSize,
void *  memChain,
uint  nextOffset 
) [static]

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. block_size: the size of the blocks mem_chain: a pointer to the first block of the chain next_offset: the offset of the next field in the blocks Since 2.10


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