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/*
* 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/>.
*
*
* CoglMemoryStack provides a really simple, but lightning fast
* memory stack allocation strategy:
*
* - The underlying pool of memory is grow-only.
* - The pool is considered to be a stack which may be comprised
* of multiple smaller stacks. Allocation is done as follows:
* - If there's enough memory in the current sub-stack then the
* stack-pointer will be returned as the allocation and the
* stack-pointer will be incremented by the allocation size.
* - If there isn't enough memory in the current sub-stack
* then a new sub-stack is allocated twice as big as the current
* sub-stack or twice as big as the requested allocation size if
* that's bigger and the stack-pointer is set to the start of the
* new sub-stack.
* - Allocations can't be freed in a random-order, you can only
* rewind the entire stack back to the start. There is no
* the concept of stack frames to allow partial rewinds.
*
* For example; we plan to use this in our tesselator which has to
* allocate lots of small vertex, edge and face structures because
* when tesselation has been finished we just want to free the whole
* lot in one go.
*
*
* Authors:
* Robert Bragg <robert@linux.intel.com>
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "cogl-memory-stack-private.h"
#include "cogl-queue.h"
#include <stdint.h>
#include <glib.h>
typedef struct _CoglMemorySubStack CoglMemorySubStack;
COGL_TAILQ_HEAD (CoglMemorySubStackList, CoglMemorySubStack);
struct _CoglMemorySubStack
{
COGL_TAILQ_ENTRY (CoglMemorySubStack) list_node;
size_t bytes;
uint8_t *data;
};
struct _CoglMemoryStack
{
CoglMemorySubStackList sub_stacks;
CoglMemorySubStack *sub_stack;
size_t sub_stack_offset;
};
static CoglMemorySubStack *
_cogl_memory_sub_stack_alloc (size_t bytes)
{
CoglMemorySubStack *sub_stack = g_slice_new (CoglMemorySubStack);
sub_stack->bytes = bytes;
sub_stack->data = g_malloc (bytes);
return sub_stack;
}
static void
_cogl_memory_stack_add_sub_stack (CoglMemoryStack *stack,
size_t sub_stack_bytes)
{
CoglMemorySubStack *sub_stack =
_cogl_memory_sub_stack_alloc (sub_stack_bytes);
COGL_TAILQ_INSERT_TAIL (&stack->sub_stacks, sub_stack, list_node);
stack->sub_stack = sub_stack;
stack->sub_stack_offset = 0;
}
CoglMemoryStack *
_cogl_memory_stack_new (size_t initial_size_bytes)
{
CoglMemoryStack *stack = g_slice_new0 (CoglMemoryStack);
COGL_TAILQ_INIT (&stack->sub_stacks);
_cogl_memory_stack_add_sub_stack (stack, initial_size_bytes);
return stack;
}
void *
_cogl_memory_stack_alloc (CoglMemoryStack *stack, size_t bytes)
{
CoglMemorySubStack *sub_stack;
void *ret;
sub_stack = stack->sub_stack;
if (G_LIKELY (sub_stack->bytes - stack->sub_stack_offset >= bytes))
{
ret = sub_stack->data + stack->sub_stack_offset;
stack->sub_stack_offset += bytes;
return ret;
}
/* If the stack has been rewound and then a large initial allocation
* is made then we may need to skip over one or more of the
* sub-stacks that are too small for the requested allocation
* size... */
for (sub_stack = sub_stack->list_node.tqe_next;
sub_stack;
sub_stack = sub_stack->list_node.tqe_next)
{
if (sub_stack->bytes >= bytes)
{
ret = sub_stack->data;
stack->sub_stack = sub_stack;
stack->sub_stack_offset = bytes;
return ret;
}
}
/* Finally if we couldn't find a free sub-stack with enough space
* for the requested allocation we allocate another sub-stack that's
* twice as big as the last sub-stack or twice as big as the
* requested allocation if that's bigger.
*/
sub_stack = COGL_TAILQ_LAST (&stack->sub_stacks, CoglMemorySubStackList);
_cogl_memory_stack_add_sub_stack (stack, MAX (sub_stack->bytes, bytes) * 2);
sub_stack = COGL_TAILQ_LAST (&stack->sub_stacks, CoglMemorySubStackList);
stack->sub_stack_offset += bytes;
return sub_stack->data;
}
void
_cogl_memory_stack_rewind (CoglMemoryStack *stack)
{
stack->sub_stack = COGL_TAILQ_FIRST (&stack->sub_stacks);
stack->sub_stack_offset = 0;
}
static void
_cogl_memory_sub_stack_free (CoglMemorySubStack *sub_stack)
{
g_free (sub_stack->data);
g_slice_free (CoglMemorySubStack, sub_stack);
}
void
_cogl_memory_stack_free (CoglMemoryStack *stack)
{
CoglMemorySubStack *sub_stack;
while ((sub_stack = COGL_TAILQ_FIRST (&stack->sub_stacks)))
{
COGL_TAILQ_REMOVE (&stack->sub_stacks, sub_stack, list_node);
_cogl_memory_sub_stack_free (sub_stack);
}
g_slice_free (CoglMemoryStack, stack);
}
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