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<?php
namespace Amp\Loop\Internal;
use Amp\Loop\Watcher;
/**
* Uses a binary tree stored in an array to implement a heap.
*/
final class TimerQueue
{
/** @var Watcher[] */
private $data = [];
/** @var int[] */
private $pointers = [];
/**
* @param int $node Rebuild the data array from the given node upward.
*
* @return void
*/
private function heapifyUp(int $node)
{
$entry = $this->data[$node];
while ($node !== 0 && $entry->expiration < $this->data[$parent = ($node - 1) >> 1]->expiration) {
$this->swap($node, $parent);
$node = $parent;
}
}
/**
* @param int $node Rebuild the data array from the given node downward.
*
* @return void
*/
private function heapifyDown(int $node)
{
$length = \count($this->data);
while (($child = ($node << 1) + 1) < $length) {
if ($this->data[$child]->expiration < $this->data[$node]->expiration
&& ($child + 1 >= $length || $this->data[$child]->expiration < $this->data[$child + 1]->expiration)
) {
// Left child is less than parent and right child.
$swap = $child;
} elseif ($child + 1 < $length && $this->data[$child + 1]->expiration < $this->data[$node]->expiration) {
// Right child is less than parent and left child.
$swap = $child + 1;
} else { // Left and right child are greater than parent.
break;
}
$this->swap($node, $swap);
$node = $swap;
}
}
private function swap(int $left, int $right)
{
$temp = $this->data[$left];
$this->data[$left] = $this->data[$right];
$this->pointers[$this->data[$right]->id] = $left;
$this->data[$right] = $temp;
$this->pointers[$temp->id] = $right;
}
/**
* Inserts the watcher into the queue. Time complexity: O(log(n)).
*
* @param Watcher $watcher
*
* @psalm-param Watcher<int> $watcher
*
* @return void
*/
public function insert(Watcher $watcher)
{
\assert($watcher->expiration !== null);
\assert(!isset($this->pointers[$watcher->id]));
$node = \count($this->data);
$this->data[$node] = $watcher;
$this->pointers[$watcher->id] = $node;
$this->heapifyUp($node);
}
/**
* Removes the given watcher from the queue. Time complexity: O(log(n)).
*
* @param Watcher $watcher
*
* @psalm-param Watcher<int> $watcher
*
* @return void
*/
public function remove(Watcher $watcher)
{
$id = $watcher->id;
if (!isset($this->pointers[$id])) {
return;
}
$this->removeAndRebuild($this->pointers[$id]);
}
/**
* Deletes and returns the Watcher on top of the heap if it has expired, otherwise null is returned.
* Time complexity: O(log(n)).
*
* @param int $now Current loop time.
*
* @return Watcher|null Expired watcher at the top of the heap or null if the watcher has not expired.
*
* @psalm-return Watcher<int>|null
*/
public function extract(int $now)
{
if (empty($this->data)) {
return null;
}
$watcher = $this->data[0];
if ($watcher->expiration > $now) {
return null;
}
$this->removeAndRebuild(0);
return $watcher;
}
/**
* Returns the expiration time value at the top of the heap. Time complexity: O(1).
*
* @return int|null Expiration time of the watcher at the top of the heap or null if the heap is empty.
*/
public function peek()
{
return isset($this->data[0]) ? $this->data[0]->expiration : null;
}
/**
* @param int $node Remove the given node and then rebuild the data array.
*
* @return void
*/
private function removeAndRebuild(int $node)
{
$length = \count($this->data) - 1;
$id = $this->data[$node]->id;
$left = $this->data[$node] = $this->data[$length];
$this->pointers[$left->id] = $node;
unset($this->data[$length], $this->pointers[$id]);
if ($node < $length) { // don't need to do anything if we removed the last element
$parent = ($node - 1) >> 1;
if ($parent >= 0 && $this->data[$node]->expiration < $this->data[$parent]->expiration) {
$this->heapifyUp($node);
} else {
$this->heapifyDown($node);
}
}
}
}
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