dmmlib/src/coalesce.c

#include "coalesce.h"
#include "block_header.h"
#include "other.h"

void * coalesce(void *ptr, heap_t *heap) {
    void *prev;
    int fixed_list_id, i;
    maptable_node_t *current_maptable_node;

    // If there is a negative value on max_coalesce_size, then don't do
    // anything.
    // FIXME To be moved in custom_free()
    if(heap->dmm_knobs.max_coalesce_size < 0) {
        return ptr;
    }

    // Try to coalesce with the previous memory block
    // FIXME What happens if we have multiple heaps and we don't know the
    // owner of the blocks?
    if(is_previous_free(ptr)) {
        prev = get_previous(ptr);

        // Check if it is a block of a fixed list
        fixed_list_id = map_size_to_list(heap, get_size(prev));
        if(fixed_list_id != -1) {
            // If it is, find the fixed list and remove the block
            current_maptable_node = heap->maptable_head;
            if(fixed_list_id != 0) {
                for(i = 1; i < fixed_list_id; i++) {
                    current_maptable_node = current_maptable_node->next;
                }
            }
            remove_block(ptr, current_maptable_node->fixed_list_head);
        } else {
            // Or it is a block from the free list, so remove it
            // from there
            remove_block(ptr, heap->free_list_head);
        }

        // Set the new size
        // Note: the rest of the header variables will be set on free().
        set_size(prev, get_size(prev) + get_size(ptr) + HEADER_SIZE);

        return prev;
    } else {
        return ptr;
    }
}