0ad/source/lib/allocators/bucket.cpp

/* Copyright (c) 2010 Wildfire Games
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/*
 * bucket allocator
 */

#include "precompiled.h"
#include "lib/allocators/bucket.h"

#include "lib/alignment.h"
#include "lib/allocators/freelist.h"


// power-of-2 isn't required; value is arbitrary.
const size_t bucketSize = 4000;


Status bucket_create(Bucket* b, size_t el_size)
{
	b->freelist = mem_freelist_Sentinel();
	b->el_size = Align<allocationAlignment>(el_size);

	// note: allocating here avoids the is-this-the-first-time check
	// in bucket_alloc, which speeds things up.
	b->bucket = (u8*)malloc(bucketSize);
	if(!b->bucket)
	{
		// cause next bucket_alloc to retry the allocation
		b->pos = bucketSize;
		b->num_buckets = 0;
		WARN_RETURN(ERR::NO_MEM);
	}

	*(u8**)b->bucket = 0;	// terminate list
	b->pos = Align<allocationAlignment>(sizeof(u8*));
	b->num_buckets = 1;
	return INFO::OK;
}


void bucket_destroy(Bucket* b)
{
	while(b->bucket)
	{
		u8* prev_bucket = *(u8**)b->bucket;
		free(b->bucket);
		b->bucket = prev_bucket;
		b->num_buckets--;
	}

	ENSURE(b->num_buckets == 0);

	// poison pill: cause subsequent alloc and free to fail
	b->freelist = 0;
	b->el_size = bucketSize;
}


void* bucket_alloc(Bucket* b, size_t size)
{
	size_t el_size = b->el_size? b->el_size : Align<allocationAlignment>(size);
	// must fit in a bucket
	ENSURE(el_size <= bucketSize-sizeof(u8*));

	// try to satisfy alloc from freelist
	void* el = mem_freelist_Detach(b->freelist);
	if(el)
		return el;

	// if there's not enough space left, close current bucket and
	// allocate another.
	if(b->pos+el_size > bucketSize)
	{
		u8* bucket = (u8*)malloc(bucketSize);
		if(!bucket)
			return 0;
		*(u8**)bucket = b->bucket;
		b->bucket = bucket;
		// skip bucket list field and align (note: malloc already
		// aligns to at least 8 bytes, so don't take b->bucket into account)
		b->pos = Align<allocationAlignment>(sizeof(u8*));;
		b->num_buckets++;
	}

	void* ret = b->bucket+b->pos;
	b->pos += el_size;
	return ret;
}


void* bucket_fast_alloc(Bucket* b)
{
	// try to satisfy alloc from freelist
	void* el = mem_freelist_Detach(b->freelist);
	if(el)
		return el;

	// if there's not enough space left, close current bucket and
	// allocate another.
	if(b->pos+b->el_size > bucketSize)
	{
		u8* bucket = (u8*)malloc(bucketSize);
		*(u8**)bucket = b->bucket;
		b->bucket = bucket;
		// skip bucket list field (alignment is only pointer-size)
		b->pos = sizeof(u8*);
		b->num_buckets++;
	}

	void* ret = b->bucket+b->pos;
	b->pos += b->el_size;
	return ret;
}


void bucket_free(Bucket* b, void* el)
{
	if(b->el_size == 0)
	{
		DEBUG_WARN_ERR(ERR::LOGIC);	// cannot free variable-size items
		return;
	}

	mem_freelist_AddToFront(b->freelist, el);

	// note: checking if <el> was actually allocated from <b> is difficult:
	// it may not be in the currently open bucket, so we'd have to
	// iterate over the list - too much work.
}