multiple php function instances

I've got a function which calculates some data from a table, a put's it into another, it takes a while for the whole process, about 30 mins or something like that. The function calculates statistics for each day for a couple of months period, but after like 10 days, it starts another thread while continuing another one, and then another one, and another, so i get a table full of random crap in the end.

Why does it start another instance of the function while the other one isn't finished?

Here's the function:

function build_fill_array() {

$sql = db_fetch_object(db_query("SELECT min(timestamp) as min FROM {accesslog}"));
$nids = db_query("SELECT nid FROM {node} WHERE type='raamat'");
while($nid_array = db_fetch_array($nids)) {
    $nid[] = $nid_array['nid'];
}
$start_ts = $sql->min;
$end_ts = mktime(0,0,0, date('m'), date('d'), date('Y'));
$start_ts = mktime(0,0,0, date('m', $start_ts), date('d', $start_ts), date('Y', $start_ts));

while($start_ts != $end_ts) {
    $day = date('d.m.Y', $start_ts);
    $range_from = mktime(0,0,0, date('m', $start_ts), date('d', $start_ts), date('Y', $start_ts));
    $range_to = mktime(23,59,59, date('m', $start_ts), date('d', $start_ts), date('Y', $start_ts));
    foreach($nid as $n) {
    $results = db_fetch_object(db_query("SELECT count(hostname) as total, count(distinct hostname) as visits FROM {accesslog} WHERE timestamp BETWEEN %d AND %d AND path = 'node/%d'", $range_from, $range_to, $n));
    $sql_insert = "INSERT INTO {statistics_view} (`id`, `nid`, `total`, `unique`, `timestamp`, `date`) VALUES (NULL, $n, $results->total, $results->visits, ".mktime().", '$day');";
    db_query($sql_insert); 
  }


    $start_ts = mktime(0,0,0, date('m', $start_ts), date('d', $start_ts)+1, date('Y', $start_ts));
}

}

Edit: don't mind the {} around table names, it's a drup开发者_JAVA百科al thing.

Why does it start another instance of the function while the other one isn't finished?

You should look at where the function is called, not the function itself.

Replace

while($start_ts != $end_ts) {

with:

while($start_ts <= $end_ts) {