SplPriorityQueue::compare()

(PHP 5 >= 5.3.0, PHP 7)

Compare priorities in order to place elements correctly in the heap while sifting up

说明

publicSplPriorityQueue::compare(mixed $priority1, mixed $priority2) : int

Compare $priority1with $priority2.

参数

$priority1

The priority of the first node being compared.

$priority2

The priority of the second node being compared.

返回值

Result of the comparison, positive integer if $priority1 is greater than $priority2, 0 if they are equal, negative integer otherwise.

Note:

Multiple elements with the same priority will get dequeued in no particular order.

At this time, the documentation sais "Note: Multiple elements with the same priority will get dequeued in no particular order."
If you need elements of equal priority to maintain insertion order, you can use something like:
<?php
class StablePriorityQueue extends SplPriorityQueue {
  protected $serial = PHP_INT_MAX;
  public function insert($value, $priority) {
    parent::insert($value, array($priority, $this->serial--));
  }
}
?>