rowio/get.c

Go to the documentation of this file.

#include <stdio.h>
#include <grass/rowio.h>

static void *my_select(ROWIO *, int);
static void pageout(ROWIO *, int);


void *rowio_get(ROWIO * R, int row)
{
    int i;
    int age;
    int cur;

    if (row < 0)
        return NULL;

    if (row == R->cur)
        return R->buf;

    for (i = 0; i < R->nrows; i++)
        if (row == R->rcb[i].row)
            return my_select(R, i);

    age = 0;
    cur = 0;

    for (i = 0; i < R->nrows; i++)
        if (R->rcb[i].row < 0) {        /* free slot ! */
            cur = i;
            break;
        }
        else if (age < R->rcb[i].age) {
            cur = i;
            age = R->rcb[i].age;
        }

    pageout(R, cur);

    i = (*R->getrow) (R->fd, R->rcb[cur].buf, R->rcb[cur].row = row, R->len);
    R->rcb[cur].dirty = 0;
    if (!i) {
        R->rcb[cur].row = -1;
        if (cur == R->cur)
            R->cur = -1;
        return NULL;
    }

    return my_select(R, cur);
}

void rowio_flush(ROWIO * R)
{
    int i;

    for (i = 0; i < R->nrows; i++)
        pageout(R, i);
}

static void pageout(ROWIO * R, int cur)
{
    if (R->rcb[cur].row < 0)
        return;
    if (!R->rcb[cur].dirty)
        return;
    (*R->putrow) (R->fd, R->rcb[cur].buf, R->rcb[cur].row, R->len);
    R->rcb[cur].dirty = 0;
}

static void *my_select(ROWIO * R, int n)
{
    int i;

    R->rcb[n].age = 0;
    for (i = 0; i < R->nrows; i++)
        R->rcb[i].age++;
    R->cur = R->rcb[n].row;
    R->buf = R->rcb[n].buf;
    return R->buf;
}