A 500 error has occurred - Executing long loop within PHP - php

Question

A 500 error has occurred - executing long loop with PHP.
I am currently working on a scheduling system to schedule nurses on a hospital ward, I am using a genetic algorithm to carry this out.
so I randomly allocate each nurses to a shift.
and then work out how fit they are for the shift.
I then kill off any allocation which do not meet my fitness level.
I then randomly allocate a new timetable.
Assess that for fitness
kill off any allocation which do not meet my fitness level.
Merge the two timetables, keeping the fitness allocations
I loop through generating random timetable, accessing its fitness and merging the timetables
This works fine while looping through 30 - 100 times
Once I go past the 100 mark it sometimes fails - a 500 error has occurred
This always occurs when it takes over 2:30mins to complete the script
So I'm making the assumption at some point my server times out for taking too long?
I have added <?php set_time_limit(3600);
This is at the top of my file, not inside the constructor, or the class. Is it in the right place?
it still times out at 2 and a half minute,
Here is my code, the loop is the 200 loop
Still need to refractor my code so don't be too judgmental
<?php
set_time_limit(3600);
* Description of scheduler
*
* #author Dela
*/
include ("randomTtAllocation.php");
include ("fittness.php");
class scheduler {
private $randomTimetable;
private $timetable;
private $weight;
private $newTimetable ;
private $newWeight;
function __construct($labs,$students) {
echo "helloworld";
// create random timetable and print it
$r = new randomTtAllocation();
$this->randomTimetable = $r->__randomAllocation($labs, $students);
//echo "<br>" . " ............initial Time Table............." . "<br>" ;
echo "<br>";
echo "<br>";
echo "<br>";
$this->__printTt($this->randomTimetable, $this->randomTimetable);
// work out fittness for the timetable, return fit results and print
$fit = new fittness( $this->randomTimetable, $labs, $students , $r->__getNumOfSessions());
$this->newWeight = $fit->__getnewWeight();
$this->newTimetable = $fit->__getnewTimetable();;
//echo "<br>" . " ............newTimetable.........newWeight...." . "<br>" ;
//$this->__printTt($this->newTimetable, $this->newWeight );
// sort
$this->__sortTtByWeight();
$this->timetable = $this->newTimetable;
$this->weight = $this->newWeight;
for ($i = 0; $i < 200; $i++) {
// create second time table
$this->randomTimetable = $r->__randomAllocation($labs, $students);
// echo "<br>" . " ............initial Time Table............." . "<br>" ;
// $this->__printTt($this->randomTimetable, $this->randomTimetable);
// work out fittness for the timetable, return fit results and print
$fit = new fittness( $this->randomTimetable, $labs, $students , $r->__getNumOfSessions());
$this->newWeight = $fit->__getnewWeight();
$this->newTimetable = $fit->__getnewTimetable();
//echo "<br>" . " ............tempTimetable.........tempWeight...." . "<br>" ;
//$this->__printTt($this->newTimetable, $this->timetable );
$this->__sortTtByWeight();
// merge timetables
echo "<br>" . " ......old...........new." . "<br>" ;
$this->__printTt($this->timetable,$this->newTimetable );
$this->__mergeTimetables($this->newTimetable, $this->newWeight );
//echo "<br>" . " ........... mergedTimetable.........newWeight...." . "<br>" ;
//$this->__printTt($this->timetable,$this->weight );
// fittness of new timetable
$fit = new fittness( $this->timetable, $labs, $students , $r->__getNumOfSessions());
echo "<br>" . " ......merged.......kulled" . "<br>" ;
$this->__printTt($this->timetable,$fit->__getnewTimetable() );
$this->weight = $fit->__getnewWeight();
$this->timetable = $fit->__getnewTimetable();
$c[$i] = $this->__countSlotsAllocated();
echo "<br> ". $i;
}
print_r($c);
}
// sorts the re allocated time table by weight
function __sortTtByWeight() {
// for each slot
foreach($this->newTimetable as $l => $i_value) {
$size = 0;
// see how many sessions they are taking
while ($this->newTimetable[$l][$size] != "null") {
if ($this->newTimetable[$l][$size] == "0") {
break;
}
$size++;
}
for ($i = 1; $i < $size; $i++) {
$key = $this->newWeight[$l][$i];
$key1 = $this->newTimetable[$l][$i];
$k = $i - 1;
while ($k >= 0 && $this->newWeight[$l][$k] < $key) {
$this->newWeight[$l][$k + 1] = $this->newWeight[$l][$k];
$this->newTimetable[$l][$k + 1] = $this->newTimetable[$l][$k];
$k--;
}
$this->newTimetable[$l][$k + 1] = $key1;
$this->newWeight[$l][$k + 1] = $key;
}
}
}
function __countSlotsAllocated() {
$count = 0;
foreach($this->timetable as $i => $x_value) {
$j = 0;
while (($this->timetable[$i][$j] != "null") && ($this->timetable[$i][$j] != "0")){
$count++;
$j++;
}
}
echo "count " . $count;
return $count;
}
function __mergeTimetables($tempTimeTable,$tempWeight) {
// for each session
foreach($this->newTimetable as $i => $i_value) {
$j = 0;
$k = 0;
// while there are still students
while (($tempTimeTable[$i][$j] != "null") && ($tempTimeTable[$i][$j] != "0")) {
//echo $tempTimeTable[$i][$j];
// System.out.println(timeTable[i][k]);
// see if there is a free gap
while ($this->timetable[$i][$k] != "null") {
// if student is already taking that session
if ($tempTimeTable[$i][$j] == $this->timetable[$i][$k]) {
break;
}
if ($this->timetable[$i][$k] == "0") {
$this->timetable[$i][$k] = $tempTimeTable[$i][$j];
$this->weight[$i][$k] = $tempWeight[$i][$j];
break;
}
$k++;
}
if ($this->timetable[$i][$k] == "null") {
if ($tempWeight[$i][$j] < $this->weight[$i][0]) {
$this->timetable[$i][0] = $tempTimeTable[$i][$j];
$this->weight[$i][0] = $tempWeight[$i][$j];
}
}
$j++;
}
}
}
function __returnTimetable() {
return $this->timetable;
}
function __printTt($timetable, $weight) {
foreach($timetable as $x => $x_value) {
for ($i = 0; $i < 5; $i++) {
echo $timetable[$x][$i] . " ";
}
echo " . . . . .";
for ($i = 0; $i < 5; $i++) {
echo $weight[$x][$i] . " ";
}
echo "<br>";
}
}
}

Answer 1

Normally you shouldn't do all this work within the http request. Instead you should start a background task and have the web page show progress on the job.
The php configuration has a time limit per request which you can adjust, but it's not expected by users to take so long.