1-1
1-2
1-3
1-4

1-2->2-1
1-4->3-4
 
2-1
2-2
2-3
2-4

2-2->1-3
2-4->3-3

3-1
3-2
3-3
3-4

3-2->2-3

##</code><code>##

foreach $pid (@p_s) 
{
 #...rest of scheduler loop
}