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FS#9916 buflib plugin memory allocator

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@20202 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Andrew Mahone 2009-03-04 21:11:12 +00:00
parent e54c1cc9a2
commit b727de604d
3 changed files with 367 additions and 0 deletions
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1
apps/plugins/lib/SOURCES
View file

@ -4,6 +4,7 @@ configfile.c
fixedpoint.c
playback_control.c
rgb_hsv.c
buflib.c
#if defined(HAVE_LCD_BITMAP) && (LCD_DEPTH < 4)
/*
The scaler is not provided in core on mono targets, but is built in

308
apps/plugins/lib/buflib.c Normal file
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@ -0,0 +1,308 @@
/***************************************************************************
* __________ __ ___.
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
* \/ \/ \/ \/ \/
* $Id$
*
* This is a memory allocator designed to provide reasonable management of free
* space and fast access to allocated data. More than one allocator can be used
* at a time by initializing multiple contexts.
*
* Copyright (C) 2009 Andrew Mahone
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/
#include "buflib.h"
/* The main goal of this design is fast fetching of the pointer for a handle.
* For that reason, the handles are stored in a table at the end of the buffer
* with a fixed address, so that returning the pointer for a handle is a simple
* table lookup. To reduce the frequency with which allocated blocks will need
* to be moved to free space, allocations grow up in address from the start of
* the buffer. The buffer is treated as an array of union buflib_data. Blocks
* start with a length marker, which is included in their length. Free blocks
* are marked by negative length, allocated ones use the second buflib_data in
* the block to store a pointer to their handle table entry, so that it can be
* quickly found and updated during compaction. The allocator functions are
* passed a context struct so that two allocators can be run, for example, one
* per core may be used, with convenience wrappers for the single-allocator
* case that use a predefined context.
*/
#define ABS(x) \
({ \
typeof(x) xtmp_abs_ = x; \
xtmp_abs_ = xtmp_abs_ < 0 ? -xtmp_abs_ : xtmp_abs_; \
xtmp_abs_; \
})
/* Initialize buffer manager */
void
buflib_init(struct buflib_context *ctx, void *buf, size_t size)
{
union buflib_data *bd_buf = buf;
/* Align on sizeof(buflib_data), to prevent unaligned access */
ALIGN_BUFFER(bd_buf, size, sizeof(union buflib_data));
size /= sizeof(union buflib_data);
/* The handle table is initialized with no entries */
ctx->handle_table = bd_buf + size;
ctx->last_handle = bd_buf + size;
ctx->first_free_handle = bd_buf + size - 1;
ctx->first_free_block = bd_buf;
/* A marker is needed for the end of allocated data, to make sure that it
* does not collide with the handle table, and to detect end-of-buffer.
*/
ctx->alloc_end = bd_buf;
ctx->compact = true;
}
/* Allocate a new handle, returning 0 on failure */
static inline
union buflib_data* handle_alloc(struct buflib_context *ctx)
{
union buflib_data *handle;
/* first_free_handle is a lower bound on free handles, work through the
* table from there until a handle containing NULL is found, or the end
* of the table is reached.
*/
for (handle = ctx->first_free_handle; handle >= ctx->last_handle; handle--)
if (!handle->ptr)
break;
/* If the search went past the end of the table, it means we need to extend
* the table to get a new handle.
*/
if (handle < ctx->last_handle)
{
if (handle >= ctx->alloc_end)
ctx->last_handle--;
else
return NULL;
}
handle->val = -1;
return handle;
}
/* Free one handle, shrinking the handle table if it's the last one */
static inline
void handle_free(struct buflib_context *ctx, union buflib_data *handle)
{
handle->ptr = 0;
/* Update free handle lower bound if this handle has a lower index than the
* old one.
*/
if (handle > ctx->first_free_handle)
ctx->first_free_handle = handle;
if (handle == ctx->last_handle)
ctx->last_handle++;
else
ctx->compact = false;
}
/* Shrink the handle table, returning true if its size was reduced, false if
* not
*/
static inline
bool
handle_table_shrink(struct buflib_context *ctx)
{
bool rv;
union buflib_data *handle;
for (handle = ctx->last_handle; !(handle->ptr); handle++);
if (handle > ctx->first_free_handle)
ctx->first_free_handle = handle - 1;
rv = handle == ctx->last_handle;
ctx->last_handle = handle;
return rv;
}
/* Compact allocations and handle table, adjusting handle pointers as needed.
* Return true if any space was freed or consolidated, false otherwise.
*/
static bool
buflib_compact(struct buflib_context *ctx)
{
union buflib_data *block = ctx->first_free_block, *new_block;
int shift = 0, len;
/* Store the results of attempting to shrink the handle table */
bool ret = handle_table_shrink(ctx);
for(; block != ctx->alloc_end; block += len)
{
len = block->val;
/* This block is free, add its length to the shift value */
if (len < 0)
{
shift += len;
len = -len;
continue;
}
/* If shift is non-zero, it represents the number of places to move
* blocks down in memory. Calculate the new address for this block,
* update its entry in the handle table, and then move its contents.
*/
if (shift)
{
new_block = block + shift;
block[1].ptr->ptr = new_block + 2;
rb->memmove(new_block, block, len * sizeof(union buflib_data));
}
}
/* Move the end-of-allocation mark, and return true if any new space has
* been freed.
*/
ctx->alloc_end += shift;
ctx->first_free_block = ctx->alloc_end;
ctx->compact = true;
return ret || shift;
}
/* Allocate a buffer of size bytes, returning a handle for it */
int
buflib_alloc(struct buflib_context *ctx, size_t size)
{
union buflib_data *handle, *block;
bool last = false;
/* This really is assigned a value before use */
int block_len;
size = (size + sizeof(union buflib_data) - 1) /
sizeof(union buflib_data) + 2;
handle_alloc:
handle = handle_alloc(ctx);
if (!handle)
{
/* If allocation has failed, and compaction has succeded, it may be
* possible to get a handle by trying again.
*/
if (!ctx->compact && buflib_compact(ctx))
goto handle_alloc;
else
return 0;
}
buffer_alloc:
for (block = ctx->first_free_block;; block += block_len)
{
/* If the last used block extends all the way to the handle table, the
* block "after" it doesn't have a header. Because of this, it's easier
* to always find the end of allocation by saving a pointer, and always
* calculate the free space at the end by comparing it to the
* last_handle pointer.
*/
if(block == ctx->alloc_end)
{
last = true;
block_len = ctx->last_handle - block;
if ((size_t)block_len < size)
block = NULL;
break;
}
block_len = block->val;
/* blocks with positive length are already allocated. */
if(block_len > 0)
continue;
block_len = -block_len;
/* The search is first-fit, any fragmentation this causes will be
* handled at compaction.
*/
if ((size_t)block_len >= size)
break;
}
if (!block)
{
/* Try compacting if allocation failed, but only if the handle
* allocation did not trigger compaction already, since there will
* be no further gain.
*/
if (!ctx->compact && buflib_compact(ctx))
{
goto buffer_alloc;
} else {
handle->val=1;
handle_free(ctx, handle);
return 0;
}
}
/* Set up the allocated block, by marking the size allocated, and storing
* a pointer to the handle.
*/
block->val = size;
block[1].ptr = handle;
handle->ptr = block + 2;
/* If we have just taken the first free block, the next allocation search
* can save some time by starting after this block.
*/
if (block == ctx->first_free_block)
ctx->first_free_block += size;
block += size;
/* alloc_end must be kept current if we're taking the last block. */
if (last)
ctx->alloc_end = block;
/* Only free blocks *before* alloc_end have tagged length. */
else if ((size_t)block_len > size)
block->val = size - block_len;
/* Return the handle index as a positive integer. */
return ctx->handle_table - handle;
}
/* Free the buffer associated with handle_num. */
void
buflib_free(struct buflib_context *ctx, int handle_num)
{
union buflib_data *handle = ctx->handle_table - handle_num,
*freed_block = handle->ptr - 2,
*block = ctx->first_free_block,
*next_block = block;
/* We need to find the block before the current one, to see if it is free
* and can be merged with this one.
*/
while (next_block < freed_block)
{
block = next_block;
next_block += ABS(block->val);
}
/* If next_block == block, the above loop didn't go anywhere. If it did,
* and the block before this one is empty, we can combine them.
*/
if (next_block == freed_block && next_block != block && block->val < 0)
block->val -= freed_block->val;
/* Otherwise, set block to the newly-freed block, and mark it free, before
* continuing on, since the code below exects block to point to a free
* block which may have free space after it.
*/
else
{
block = freed_block;
block->val = -block->val;
}
next_block = block - block->val;
/* Check if we are merging with the free space at alloc_end. */
if (next_block == ctx->alloc_end)
ctx->alloc_end = block;
/* Otherwise, the next block might still be a "normal" free block, and the
* mid-allocation free means that the buffer is no longer compact.
*/
else {
ctx->compact = false;
if (next_block->val < 0)
block->val += next_block->val;
}
handle_free(ctx, handle);
handle->ptr = NULL;
/* If this block is before first_free_block, it becomes the new starting
* point for free-block search.
*/
if (block < ctx->first_free_block)
ctx->first_free_block = block;
}

58
apps/plugins/lib/buflib.h Normal file
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@ -0,0 +1,58 @@
/***************************************************************************
* __________ __ ___.
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
* \/ \/ \/ \/ \/
* $Id$
*
* This is a memory allocator designed to provide reasonable management of free
* space and fast access to allocated data. More than one allocator can be used
* at a time by initializing multiple contexts.
*
* Copyright (C) 2009 Andrew Mahone
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/
#ifndef _BUFLIB_H_
#include <plugin.h>
union buflib_data
{
intptr_t val;
union buflib_data *ptr;
};
struct buflib_context
{
union buflib_data *handle_table;
union buflib_data *first_free_handle;
union buflib_data *last_handle;
union buflib_data *first_free_block;
union buflib_data *alloc_end;
bool compact;
};
void buflib_init(struct buflib_context *context, void *buf, size_t size);
int buflib_alloc(struct buflib_context *context, size_t size);
void buflib_free(struct buflib_context *context, int handle);
/* always_inline is due to this not getting inlined when not optimizing, which
* leads to an unresolved reference since it doesn't exist as a non-inline
* function
*/
extern inline __attribute__((always_inline))
void* buflib_get_data(struct buflib_context *context, int handle)
{
return (void*)(context->handle_table[-handle].ptr);
}
#endif