source: mainline/src/mm/heap.c@ 02a99d2

/*
 * Copyright (C) 2001-2004 Jakub Jermar
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <mm/heap.h>
#include <synch/spinlock.h>
#include <func.h>
#include <memstr.h>
#include <panic.h>
#include <arch/types.h>

/*
 * First-fit algorithm.
 * Simple, but hopefully correct.
 * Chunks being freed are tested for mergability with their neighbours.
 */

static chunk_t *chunk0;
static spinlock_t heaplock;

void heap_init(__address heap, int size)
{
        spinlock_initialize(&heaplock);
        memsetb(heap,size,0);
        chunk0 = (chunk_t *) heap;
        chunk0->used = 0;
        chunk0->size = size - sizeof(chunk_t);
        chunk0->next = NULL;
        chunk0->prev = NULL;
}

/*
 * Uses first-fit algorithm.
 */
void *malloc(int size)
{
        pri_t pri;
        chunk_t *x, *y, *z;

        if (size == 0)
                panic("malloc: zero-size allocation request");
                
        x = chunk0;
        pri = cpu_priority_high();
        spinlock_lock(&heaplock);               
        while (x) {
                if (x->used || x->size < size) {
                        x = x->next;
                        continue;
                }
                
                x->used = 1;
    
                /*
                 * If the chunk exactly matches required size or if truncating
                 * it would not provide enough space for storing a new chunk
                 * header plus at least one byte of data, we are finished.
                 */
                if (x->size < size + sizeof(chunk_t) + 1) {
                        spinlock_unlock(&heaplock);
                        cpu_priority_restore(pri);
                        return &x->data[0];
                }

                /*
                 * Truncate x and create a new chunk.
                 */
                y = (chunk_t *) (((__address) x) + size + sizeof(chunk_t));
                y->used = 0;
                y->size = x->size - size - sizeof(chunk_t);
                y->prev = x;
                y->next = NULL;
                
                if (z = x->next) {
                        z->prev = y;
                        y->next = z;
                }
                
                x->size = size;
                x->next = y;
                spinlock_unlock(&heaplock);
                cpu_priority_restore(pri);

                return &x->data[0];
        }
        spinlock_unlock(&heaplock);
        cpu_priority_restore(pri);
        return NULL;
}

void free(void *ptr)
{
        pri_t pri;
        chunk_t *x, *y, *z;

        if (!ptr)
                panic("free on NULL");


        y = (chunk_t *) (((__u8 *) ptr) - sizeof(chunk_t));
        if (y->used != 1)
                panic("freeing unused/damaged chunk");

        pri = cpu_priority_high();
        spinlock_lock(&heaplock);
        x = y->prev;
        z = y->next;
        /* merge x and y */
        if (x && !x->used) {
                x->size += y->size + sizeof(chunk_t);
                x->next = z;
                if (z)
                        z->prev = x;
                y = x;
        }
        /* merge y and z or merge (x merged with y) and z */
        if (z && !z->used) {
                y->size += z->size + sizeof(chunk_t);
                y->next = z->next;
                if (z->next)  {
                        /* y is either y or x */
                        z->next->prev = y;
                }
        }
        y->used = 0;
        spinlock_unlock(&heaplock);
        cpu_priority_restore(pri);
}