Commit 1d485e56 authored by Matthias Clasen's avatar Matthias Clasen

Document the slice allocator

parent 1fe373b2
2005-12-03 Matthias Clasen <mclasen@redhat.com>
* glib/tmpl/memory_chunks.sgml: Document GMemChunk
as deprecated.
* glib/glib-docs.sgml:
* glib/glib-sections.txt:
* glib/tmpl/memory_slices.sgml: Document the slice
allocator.
2005-12-02 Matthias Clasen <mclasen@redhat.com>
* glib/building.sgml:
......
......@@ -32,6 +32,7 @@
<!ENTITY glib-Automatic-String-Completion SYSTEM "xml/completion.xml">
<!ENTITY glib-Windows-Compatability-Functions SYSTEM "xml/windows.xml">
<!ENTITY glib-Memory-Chunks SYSTEM "xml/memory_chunks.xml">
<!ENTITY glib-Memory-Slices SYSTEM "xml/memory_slices.xml">
<!ENTITY glib-Doubly-Linked-Lists SYSTEM "xml/linked_lists_double.xml">
<!ENTITY glib-Singly-Linked-Lists SYSTEM "xml/linked_lists_single.xml">
<!ENTITY glib-Double-ended-Queues SYSTEM "xml/queue.xml">
......@@ -153,6 +154,7 @@ synchronize their operation.
<chapter id="glib-data-types">
<title>GLib Data Types</title>
&glib-Memory-Slices;
&glib-Memory-Chunks;
&glib-Doubly-Linked-Lists;
&glib-Singly-Linked-Lists;
......
......@@ -1566,6 +1566,26 @@ g_mem_chunk_print
</SECTION>
<SECTION>
<TITLE>Memory Slices</TITLE>
<FILE>memory_slices</FILE>
g_slice_alloc
g_slice_alloc0
g_slice_free1
g_slice_free_chain
<SUBSECTION>
g_slice_new
g_slice_new0
g_slice_free
<SUBSECTION Private>
GSliceConfig
g_slice_set_config
g_slice_get_config
g_slice_get_config_state
</SECTION>
<SECTION>
<TITLE>Doubly-Linked Lists</TITLE>
<FILE>linked_lists_double</FILE>
......
......@@ -2,15 +2,18 @@
Memory Chunks
<!-- ##### SECTION Short_Description ##### -->
efficient way to allocate groups of equal-sized chunks of memory.
deprecated way to allocate groups of equal-sized chunks of memory.
<!-- ##### SECTION Long_Description ##### -->
<para>
Memory chunks provide an efficient way to allocate equal-sized pieces of
memory, called atoms. They are used extensively within GLib itself.
For example, the
<link linkend="glib-Doubly-Linked-lists">Doubly Linked Lists</link>
use memory chunks to allocate space for elements of the lists.
Memory chunks provide an space-efficient way to allocate equal-sized
pieces of memory, called atoms. However, due to the administrative
overhead (in particular for #G_ALLOC_AND_FREE, and when used from multiple
threads), they are in practise often slower than direct use of g_malloc().
Therefore, memory chunks have been deprecated in favor of the
<link linkend="glib-Memory-Slices">slice allocator</link>,
which has been added in 2.10. All internal uses of memory chunks in
GLib have been converted to the <literal>g_slice</literal> API.
</para>
<para>
There are two types of memory chunks, #G_ALLOC_ONLY, and #G_ALLOC_AND_FREE.
......@@ -167,6 +170,8 @@ the atoms.
#G_ALLOC_ONLY is quicker, since it does not need to track free atoms,
but it obviously wastes memory if you no longer need many of the atoms.
@Returns: the new #GMemChunk.
@Deprecated: Use the <link linkend="glib-Memory-Slices">slice allocator</link>
instead
<!-- ##### FUNCTION g_mem_chunk_alloc ##### -->
......@@ -176,6 +181,7 @@ Allocates an atom of memory from a #GMemChunk.
@mem_chunk: a #GMemChunk.
@Returns: a pointer to the allocated atom.
@Deprecated: Use g_slice_alloc() instead
<!-- ##### FUNCTION g_mem_chunk_alloc0 ##### -->
......@@ -185,6 +191,7 @@ Allocates an atom of memory from a #GMemChunk, setting the memory to 0.
@mem_chunk: a #GMemChunk.
@Returns: a pointer to the allocated atom.
@Deprecated: Use g_slice_alloc0() instead
<!-- ##### FUNCTION g_mem_chunk_free ##### -->
......@@ -196,6 +203,7 @@ This should only be called if the #GMemChunk was created with
@mem_chunk: a #GMemChunk.
@mem: a pointer to the atom to free.
@Deprecated: Use g_slice_free1() instead
<!-- ##### FUNCTION g_mem_chunk_destroy ##### -->
......@@ -204,6 +212,8 @@ Frees all of the memory allocated for a #GMemChunk.
</para>
@mem_chunk: a #GMemChunk.
@Deprecated: Use the <link linkend="glib-Memory-Slices">slice allocator</link>
instead
<!-- ##### MACRO g_mem_chunk_create ##### -->
......@@ -223,6 +233,8 @@ the atom size.
#G_ALLOC_ONLY is quicker, since it does not need to track free atoms,
but it obviously wastes memory if you no longer need many of the atoms.
@Returns: the new #GMemChunk.
@Deprecated: Use the <link linkend="glib-Memory-Slices">slice allocator</link>
instead
<!-- ##### MACRO g_chunk_new ##### -->
......@@ -235,6 +247,7 @@ the given type, avoiding a type cast in the source code.
@type: the type of the #GMemChunk atoms, typically a structure name.
@chunk: a #GMemChunk.
@Returns: a pointer to the allocated atom, cast to a pointer to @type.
@Deprecated: Use g_slice_new() instead
<!-- ##### MACRO g_chunk_new0 ##### -->
......@@ -247,6 +260,7 @@ the given type, avoiding a type cast in the source code.
@type: the type of the #GMemChunk atoms, typically a structure name.
@chunk: a #GMemChunk.
@Returns: a pointer to the allocated atom, cast to a pointer to @type.
@Deprecated: Use g_slice_new0() instead
<!-- ##### MACRO g_chunk_free ##### -->
......@@ -259,6 +273,7 @@ and g_chunk_new0().
@mem: a pointer to the atom to be freed.
@mem_chunk: a #GMemChunk.
@Deprecated: Use g_slice_free() instead
<!-- ##### FUNCTION g_mem_chunk_reset ##### -->
......@@ -268,6 +283,8 @@ It frees all of the currently allocated blocks of memory.
</para>
@mem_chunk: a #GMemChunk.
@Deprecated: Use the <link linkend="glib-Memory-Slices">slice allocator</link>
instead
<!-- ##### FUNCTION g_mem_chunk_clean ##### -->
......@@ -276,6 +293,8 @@ Frees any blocks in a #GMemChunk which are no longer being used.
</para>
@mem_chunk: a #GMemChunk.
@Deprecated: Use the <link linkend="glib-Memory-Slices">slice allocator</link>
instead
<!-- ##### FUNCTION g_blow_chunks ##### -->
......@@ -283,6 +302,8 @@ Frees any blocks in a #GMemChunk which are no longer being used.
Calls g_mem_chunk_clean() on all #GMemChunk objects.
</para>
@Deprecated: Use the <link linkend="glib-Memory-Slices">slice allocator</link>
instead
<!-- ##### FUNCTION g_mem_chunk_info ##### -->
......@@ -292,6 +313,8 @@ It outputs the number of #GMemChunk objects currently allocated,
and calls g_mem_chunk_print() to output information on each one.
</para>
@Deprecated: Use the <link linkend="glib-Memory-Slices">slice allocator</link>
instead
<!-- ##### FUNCTION g_mem_chunk_print ##### -->
......@@ -302,5 +325,7 @@ the number of bytes used, and the number of blocks of memory allocated.
</para>
@mem_chunk: a #GMemChunk.
@Deprecated: Use the <link linkend="glib-Memory-Slices">slice allocator</link>
instead
<!-- ##### SECTION Title ##### -->
Memory Slices
<!-- ##### SECTION Short_Description ##### -->
efficient way to allocate groups of equal-sized chunks of memory.
<!-- ##### SECTION Long_Description ##### -->
<para>
Memory slices provide a space-efficient way to allocate equal-sized
pieces of memory, just like #GMemChunks, while avoiding their scalability
and performance problems.
</para>
<para>
To achieve these goals, the slice allocator uses a sophisticated,
layered design that has been inspired by Bonwick's slab allocator
<footnote><para><ulink url="http://citeseer.ist.psu.edu/bonwick94slab.html">[Bonwick94]</ulink> Jeff Bonwick, The slab allocator: An object-caching kernel
memory allocator. USENIX 1994, and
<ulink url="http://citeseer.ist.psu.edu/bonwick01magazines.html">[Bonwick01]</ulink> Bonwick and Jonathan Adams, Magazines and vmem: Extending the
slab allocator to many cpu's and arbitrary resources. USENIX 2001</para></footnote>.
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.
</para>
<para>
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 <literal>g_slice</literal> 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.
</para>
<example>
<title>Using the slice allocator</title>
<programlisting>
gchar *mem[10000];
gint i;
/* Allocate 10000 blocks. */
for (i = 0; i &lt; 10000; i++)
{
mem[i] = g_slice_alloc (50);
/* Fill in the memory with some junk. */
for (j = 0; j &lt; 50; j++)
mem[i][j] = i * j;
}
/* Now free all of the blocks. */
for (i = 0; i &lt; 10000; i++)
{
g_slice_free1 (50, mem[i]);
}
</programlisting></example>
<example>
<title>Using the slice allocator with data structures</title>
<programlisting>
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);
</programlisting></example>
<!-- ##### SECTION See_Also ##### -->
<para>
</para>
<!-- ##### SECTION Stability_Level ##### -->
<!-- ##### FUNCTION g_slice_alloc ##### -->
<para>
Allocates a block of memory from the slice allocator.
</para>
@block_size: the number of bytes to allocate
@Returns: a pointer to the allocated
@Since: 2.10
<!-- ##### FUNCTION g_slice_alloc0 ##### -->
<para>
Allocates a block of memory from the slice allocator, setting the
memory to 0.
</para>
@block_size: the number of bytes to allocate
@Returns: a pointer to the allocated block
@Since: 2.10
<!-- ##### FUNCTION g_slice_free1 ##### -->
<para>
Frees a block of memory. The memory must have been allocated from
the slice allocator.
</para>
@block_size: the size of the block
@mem_block: a pointer to the block to free
@Since: 2.10
<!-- ##### FUNCTION g_slice_free_chain ##### -->
<para>
Frees a linked list of memory block. The memory blocks must be equal-sized,
allocated from the slice allocator and linked together by a
<literal>next</literal> pointer stored in the @next_offset's word of
each block.
</para>
<para>
Currently, this function only supports blocks which store their
<literal>next</literal> pointer in the same position as #GSList.
Therefore, @next_offset must be 1.
</para>
@block_size: the size of the blocks
@mem_chain: a pointer to the first block
@next_offset: the offset of the <literal>next</literal> pointer
@Since: 2.10
<!-- ##### MACRO g_slice_new ##### -->
<para>
A convenience macro to allocate a block of memory from the slice allocator.
It calls g_slice_alloc() and casts the returned pointer to a pointer to
the given type, avoiding a type cast in the source code.
</para>
@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
<!-- ##### MACRO g_slice_new0 ##### -->
<para>
A convenience macro to allocate a block of memory from the slice allocator
and set the memory to 0. It calls g_slice_alloc0() and casts the returned
pointer to a pointer to the given type, avoiding a type cast in the source
code.
</para>
@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
<!-- ##### MACRO g_slice_free ##### -->
<para>
A convenience macro to free a block of memory that has been allocated
from the slice allocator. It calls g_slice_free1() using
<literal>sizeof (type)</literal> as the block size.
</para>
@type: the type of the block to free, typically a structure name
@mem_block: a pointer to the block to free
@Since: 2.10
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