void osReleaseFreeMemory()

in rts/win32/OSMem.c [281:375]
71 lines of code
10 McCabe index (conditional complexity)

void osReleaseFreeMemory(void)
{
    alloc_rec *prev_a, *a;
    alloc_rec head_a;
    block_rec *prev_fb, *fb;
    block_rec head_fb;
    char *a_end, *fb_end;

    /* go through allocs and free_blocks in lockstep, looking for allocs
       that are completely free, and uncommit them */

    head_a.base = 0;
    head_a.size = 0;
    head_a.next = allocs;
    head_fb.base = 0;
    head_fb.size = 0;
    head_fb.next = free_blocks;
    prev_a = &head_a;
    a = allocs;
    prev_fb = &head_fb;
    fb = free_blocks;

    while (a != NULL) {
        a_end = a->base + a->size;
        /* If a is freeable then there is a single freeblock in fb that
           covers it. The end of this free block must be >= the end of
           a, so skip anything in fb that ends before a. */
        while (fb != NULL && fb->base + fb->size < a_end) {
            prev_fb = fb;
            fb = fb->next;
        }

        if (fb == NULL) {
            /* If we have nothing left in fb, then neither a nor
               anything later in the list is freeable, so we are done. */
            break;
        }
        else {
            fb_end = fb->base + fb->size;
            /* We have a candidate fb. But does it really cover a? */
            if (fb->base <= a->base) {
                /* Yes, the alloc is within the free block. Now we need
                   to know if it sticks out at either end. */
                if (fb_end == a_end) {
                    if (fb->base == a->base) {
                        /* fb and a are identical, so just free fb */
                        prev_fb->next = fb->next;
                        stgFree(fb);
                        fb = prev_fb->next;
                    }
                    else {
                        /* fb begins earlier, so truncate it to not include a */
                        fb->size = a->base - fb->base;
                    }
                }
                else {
                    /* fb ends later, so we'll make fb just be the part
                       after a. First though, if it also starts earlier,
                       we make a new free block record for the before bit. */
                    if (fb->base != a->base) {
                        block_rec *new_fb;

                        new_fb =
                            (block_rec *)stgMallocBytes(sizeof(block_rec),
                                                        "osReleaseFreeMemory");
                        new_fb->base = fb->base;
                        new_fb->size = a->base - fb->base;
                        new_fb->next = fb;
                        prev_fb->next = new_fb;
                    }
                    fb->size = fb_end - a_end;
                    fb->base = a_end;
                }
                /* Now we can free the alloc */
                prev_a->next = a->next;
                if(!VirtualFree((void *)a->base, 0, MEM_RELEASE)) {
                    sysErrorBelch("freeAllMBlocks: VirtualFree MEM_RELEASE "
                                  "failed");
                    stg_exit(EXIT_FAILURE);
                }
                stgFree(a);
                a = prev_a->next;
            }
            else {
                /* Otherwise this alloc is not freeable, so go on to the
                   next one */
                prev_a = a;
                a = a->next;
            }
        }
    }

    allocs = head_a.next;
    free_blocks = head_fb.next;
}