Arena.cpp

/*
 * Copyright (C) 1998-2000 Netscape Communications Corporation.
 * Copyright (C) 2003-6 Apple Computer
 *
 * Other contributors:
 *   Nick Blievers <nickb@adacel.com.au>
 *   Jeff Hostetler <jeff@nerdone.com>
 *   Tom Rini <trini@kernel.crashing.org>
 *   Raffaele Sena <raff@netwinder.org>
 *
 * 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 2.1 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * Alternatively, the contents of this file may be used under the terms
 * of either the Mozilla Public License Version 1.1, found at
 * http://www.mozilla.org/MPL/ (the "MPL") or the GNU General Public
 * License Version 2.0, found at http://www.fsf.org/copyleft/gpl.html
 * (the "GPL"), in which case the provisions of the MPL or the GPL are
 * applicable instead of those above.  If you wish to allow use of your
 * version of this file only under the terms of one of those two
 * licenses (the MPL or the GPL) and not to allow others to use your
 * version of this file under the LGPL, indicate your decision by
 * deletingthe provisions above and replace them with the notice and
 * other provisions required by the MPL or the GPL, as the case may be.
 * If you do not delete the provisions above, a recipient may use your
 * version of this file under any of the LGPL, the MPL or the GPL.
 */

/*
 * Lifetime-based fast allocation, inspired by much prior art, including
 * "Fast Allocation and Deallocation of Memory Based on Object Lifetimes"
 * David R. Hanson, Software -- Practice and Experience, Vol. 20(1).
 */

#include "config.h"
#include "Arena.h"

#include <algorithm>
#include <stdlib.h>
#include <string.h>
#include <wtf/Assertions.h>
#include <wtf/FastMalloc.h>

using namespace std;

namespace WebCore {

#ifdef DEBUG_ARENA_MALLOC
static int i = 0;
#endif

#define ARENA_DEFAULT_ALIGN sizeof(double)
#define BIT(n) ((unsigned int)1 << (n))
#define BITMASK(n) (BIT(n) - 1)
#define CEILING_LOG2(_log2, _n)   \
    unsigned int j_ = (unsigned int)(_n);   \
    (_log2) = 0;                    \
    if ((j_) & ((j_)-1))            \
        (_log2) += 1;               \
    if ((j_) >> 16)                 \
        (_log2) += 16, (j_) >>= 16; \
    if ((j_) >> 8)                  \
        (_log2) += 8, (j_) >>= 8;   \
    if ((j_) >> 4)                  \
        (_log2) += 4, (j_) >>= 4;   \
    if ((j_) >> 2)                  \
        (_log2) += 2, (j_) >>= 2;   \
    if ((j_) >> 1)                  \
        (_log2) += 1;
#define FREE_PATTERN 0xDA

static int CeilingLog2(unsigned int i) {
    int log2;
    CEILING_LOG2(log2, i);
    return log2;
}

void InitArenaPool(ArenaPool* pool, const char*, unsigned size, unsigned align)
{
     if (align == 0)
         align = ARENA_DEFAULT_ALIGN;
     pool->mask = BITMASK(CeilingLog2(align));
     pool->first.next = NULL;
     pool->first.base = pool->first.avail = pool->first.limit = (uword)ARENA_ALIGN(&pool->first + 1);
     pool->current = &pool->first;
     pool->arenasize = size;                                  
}

void* ArenaAllocate(ArenaPool* pool, unsigned int numBytes, unsigned int& bytesAllocated)
{
    Arena* arena;
    char* returnPointer;

    ASSERT((numBytes & pool->mask) == 0);
    
    numBytes = (uword)ARENA_ALIGN(numBytes);

    // attempt to allocate from arenas at pool->current
    {
        arena = pool->current;
        do {
            if (arena->avail + numBytes <= arena->limit)  {
                pool->current = arena;
                returnPointer = (char *)arena->avail;
                arena->avail += numBytes;
                return returnPointer;
            }
        } while (NULL != (arena = arena->next));
    }

    // attempt to allocate from the heap
    {  
        unsigned int size = max(pool->arenasize, numBytes);
        size += sizeof *arena + pool->mask;  /* header and alignment slop */
#ifdef DEBUG_ARENA_MALLOC
        i++;
        printf("Malloc: %d\n", i);
#endif
        bytesAllocated = size;
        arena = (Arena*)fastMalloc(size);
        // fastMalloc will abort() if it fails, so we are guaranteed that a is not 0.
        arena->limit = (uword)arena + size;
        arena->base = arena->avail = (uword)ARENA_ALIGN(arena + 1);
        returnPointer = (char *)arena->avail;
        arena->avail += numBytes;
        // the newly allocated arena is linked after pool->current and becomes pool->current.
        arena->next = pool->current->next;
        pool->current->next = arena;
        pool->current = arena;
        if (!pool->first.next)
            pool->first.next = arena;
        return(returnPointer);
    }
}

// Free tail arenas linked after head, which may not be the true list head.
// Reset pool->current to point to head in case it pointed at a tail arena.
static void FreeArenaList(ArenaPool* pool, Arena* head)
{
    Arena** arenaPointer = &head->next;
    Arena* arena = *arenaPointer;
    if (!arena)
        return;

#ifdef DEBUG
    do {
        ASSERT(arena->base <= arena->avail && arena->avail <= arena->limit);
        arena->avail = arena->base;
        memset((void*)(arena)->avail, FREE_PATTERN, (arena)->limit - (arena)->avail)
    } while ((arena = arena->next) != 0);
    arena = *arenaPointer;
#endif

    do {
        *arenaPointer = arena->next;

#ifdef DEBUG        
        memset((void*)(arena), FREE_PATTERN, (arena)->limit - (uword)(arena));
#endif

#ifdef DEBUG_ARENA_MALLOC
        if (arena) {
            i--;
            printf("Free: %d\n", i);
        }
#endif

        fastFree(arena);
        arena = 0;
    } while ((arena = *arenaPointer) != 0);
    pool->current = head;
}

void FinishArenaPool(ArenaPool* pool)
{
    FreeArenaList(pool, &pool->first);
}

}