You have to prototype the sort function and it will pass them into the function.

my @sorted_array = sort sort_func @array;
sub sort_func($$){
  my $var1 = $_[0];
  my $var2 = $_[1];
  return $var2 <=> $var1;
}
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but it sounds like you need the hash ref also, so you can use the sort BLOCK ARRAY construct, but doing it inline makes the most sense.
Example:

my @sorted_array = sort {&sort_func($::a, $::b, $source, $data)} @arra
+y;
sub sort_func(){
  my $var1 = $_[0];
  my $var2 = $_[1];
  my $source = $_[2];
  my $data   = $_[3];
  return $data{$source}{$var2} <=> $data{$source}{$var1};
}
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