[Cogl] [PATCH] Adds a "magazine" allocator for chunks of fixed size

[Robert Bragg]

From: Robert Bragg <robert at linux.intel.com>

This adds a very minimal and fast allocator for chunks of memory of a
predetermined size. This has some similarities to to the glib slice
allocator although notably it is not thread safe and instead of
internally tracking multiple magazines for various sized allocations
the api lets you explicitly allocate a single magazine for a single
specific size and a pointer to the magazine is passed explicitly to the
allocate and free functions.

This allocator builds on the CoglMemoryStack allocator as an underlying
heap allocator and just never rewinds the stack. This means the heap is
effectively a grow only linked list of malloc()'d blocks of memory.

A CoglMagazine tracks a singly linked list of chunks of a predetermined
size and _cogl_magazine_chunk_alloc() simply unlinks and returns the
head of the list. If the list is empty it falls back to allocating from
the underlying stack.

_cogl_magazine_chunk_free() links the chunk back into the singly linked
list for re-use.

The chunk size passed to _cogl_magazine_new() is automatically rounded
to a multiple of 8 bytes to ensure that all stack allocations end up
aligned to 8 bytes. This also ensures that when a chunk is freed then it
will be large enough to store a pointer to the next free chunk as part
of a singly linked list.
---
 cogl/Makefile.am             |    2 +
 cogl/cogl-magazine-private.h |   82 ++++++++++++++++++++++++++++++++++++++++++
 cogl/cogl-magazine.c         |   78 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 162 insertions(+), 0 deletions(-)
 create mode 100644 cogl/cogl-magazine-private.h
 create mode 100644 cogl/cogl-magazine.c

diff --git a/cogl/Makefile.am b/cogl/Makefile.am
index 691d50f..5a1a5f6 100644
--- a/cogl/Makefile.am
+++ b/cogl/Makefile.am
@@ -331,6 +331,8 @@ cogl_sources_c = \
 	$(srcdir)/gl-prototypes/cogl-glsl-functions.h	\
 	$(srcdir)/cogl-memory-stack-private.h		\
 	$(srcdir)/cogl-memory-stack.c			\
+	$(srcdir)/cogl-magazine-private.h		\
+	$(srcdir)/cogl-magazine.c			\
 	$(NULL)
 
 if USE_GLIB
diff --git a/cogl/cogl-magazine-private.h b/cogl/cogl-magazine-private.h
new file mode 100644
index 0000000..07900ec
--- /dev/null
+++ b/cogl/cogl-magazine-private.h
@@ -0,0 +1,82 @@
+/*
+ * Cogl
+ *
+ * An object oriented GL/GLES Abstraction/Utility Layer
+ *
+ * Copyright (C) 2011 Intel Corporation.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ *
+ */
+
+#if !defined(__COGL_H_INSIDE__) && !defined(CLUTTER_COMPILATION)
+#error "Only <cogl/cogl.h> can be included directly."
+#endif
+
+#ifndef __COGL_MAGAZINE_PRIVATE_H__
+#define __COGL_MAGAZINE_PRIVATE_H__
+
+#include <glib.h>
+
+#include "cogl-memory-stack-private.h"
+
+G_BEGIN_DECLS
+
+typedef struct _CoglMagazineChunk CoglMagazineChunk;
+
+struct _CoglMagazineChunk
+{
+  CoglMagazineChunk *next;
+};
+
+typedef struct _CoglMagazine
+{
+  size_t chunk_size;
+
+  CoglMemoryStack *stack;
+  CoglMagazineChunk *head;
+} CoglMagazine;
+
+CoglMagazine *
+_cogl_magazine_new (size_t chunk_size, int initial_chunk_count);
+
+static inline void *
+_cogl_magazine_chunk_alloc (CoglMagazine *magazine)
+{
+  if (G_LIKELY (magazine->head))
+    {
+      CoglMagazineChunk *chunk = magazine->head;
+      magazine->head = chunk->next;
+      return chunk;
+    }
+  else
+    return _cogl_memory_stack_alloc (magazine->stack, magazine->chunk_size);
+}
+
+static inline void
+_cogl_magazine_chunk_free (CoglMagazine *magazine, void *data)
+{
+  CoglMagazineChunk *chunk = data;
+
+  chunk->next = magazine->head;
+  magazine->head = chunk;
+}
+
+void
+_cogl_magazine_free (CoglMagazine *magazine);
+
+G_END_DECLS
+
+#endif /* __COGL_MAGAZINE_PRIVATE_H__ */
diff --git a/cogl/cogl-magazine.c b/cogl/cogl-magazine.c
new file mode 100644
index 0000000..797bfcf
--- /dev/null
+++ b/cogl/cogl-magazine.c
@@ -0,0 +1,78 @@
+/*
+ * Cogl
+ *
+ * An object oriented GL/GLES Abstraction/Utility Layer
+ *
+ * Copyright (C) 2012 Intel Corporation.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ *
+ *
+ * CoglMagazine provides a really light weight allocator for chunks
+ * of memory with a pre-determined size.
+ *
+ * This allocator builds on CoglMemoryStack for making all initial
+ * allocations but never frees memory back to the stack.
+ *
+ * Memory chunks that haven't been allocated yet are stored in a
+ * singly linked, fifo, list.
+ *
+ * Allocating from a magazine is simply a question of popping an entry
+ * from the head of the fifo list. If no entries are available then
+ * instead allocate from the memory stack instead.
+ *
+ * When an entry is freed, it is put back into the fifo list for
+ * re-use.
+ *
+ * No attempt is ever made to shrink the amount of memory associated
+ * with a CoglMagazine.
+ *
+ *
+ * Authors:
+ *   Robert Bragg <robert at linux.intel.com>
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "cogl-memory-stack-private.h"
+#include "cogl-magazine-private.h"
+#include <glib.h>
+
+#define ROUND_UP_8(X) ((X + (8 - 1)) & ~(8 - 1))
+
+CoglMagazine *
+_cogl_magazine_new (size_t chunk_size, int initial_chunk_count)
+{
+  CoglMagazine *magazine = g_new0 (CoglMagazine, 1);
+
+  chunk_size = MAX (chunk_size, sizeof (CoglMagazineChunk));
+  chunk_size = ROUND_UP_8 (chunk_size);
+
+  magazine->chunk_size = chunk_size;
+  magazine->stack = _cogl_memory_stack_new (chunk_size * initial_chunk_count);
+  magazine->head = NULL;
+
+  return magazine;
+}
+
+void
+_cogl_magazine_free (CoglMagazine *magazine)
+{
+  _cogl_memory_stack_free (magazine->stack);
+  g_free (magazine);
+}
-- 
1.7.7.6