Класс SplQueue
(PHP 5 >= 5.3.0, PHP 7)
Введение
Класс SplQueue предоставляет основные функциональные возможности очереди, реализованные с использованием двусвязного списка.
Обзор классов
Содержание
- SplQueue::__construct — Создает новую очередь, реализованную с использованием двусвязного списка
- SplQueue::dequeue — Удаляет элемент из очереди
- SplQueue::enqueue — Добавляет элемент в очередь
- SplQueue::setIteratorMode — Устанавливает режим итератора
Коментарии
SplQueue inherits from SplDoublyLinkedList. So, objects of SplQueue support methods push() and pop(). But please be advised that if you use push() and pop() methods on a SplQueue object, it behaves like a stack rather than a queue.
For example:
$q = new SplQueue();
$q->push(1);
$q->push(2);
$q->push(3);
$q->pop();
print_r($q);
Above code returns:
SplQueue Object
(
[flags:SplDoublyLinkedList:private] => 4
[dllist:SplDoublyLinkedList:private] => Array
(
[0] => 1
[1] => 2
)
)
Note that 3 got popped and *not* 1.
So, please make sure that you use only enqueue() and dequeue() methods on a SplQueue object and *not* push() and pop().
You can use shift/unshift and push/pop to dequeue/undequeue and queue/unqueue respectively. Really handy for those applications that use sockets where you might not know you can't send data until you attempt to.
for example, this is a function for an application that will un-dequeue the remainder of the data if socket_write indicated it did not write the entire contents of the provided data.
<?php
function processSendQueue($socket, $sendQueue) {
while (!$sendQueue->isEmpty()) {
//shift() is the same as dequeue()
$senditem = $sendQueue->shift();
//returns the number of bytes written.
$rtn = socket_write($socket, $senditem);
if ($rtn === false) {
$sendQueue->unshift($senditem);
throw new exception("send error: " . socket_last_error($socket));
return;
}
if ($rtn < strlen($senditem) {
$sendQueue->unshift(substr($senditem, $rtn);
break;
}
}
}
?>
Take care that SplQueue::valid() is not returning true if the queue has nodes. Use isEmpty() instead:
$queue = new SplQueue();
$queue->enqueue('A');
$queue->enqueue('B');
$queue->enqueue('C');
var_dump($queue->valid()); // false
var_dump(!$queue->isEmpty()); // true
<?php
$queue = new SplQueue();
$queue->enqueue('A');
$queue->enqueue('B');
$queue->enqueue('C');
$queue->rewind();
while($queue->valid()){
echo $queue->current(),"\n";
$queue->next();
}
print_r($queue);
$queue->dequeue(); //remove first one
print_r($queue);
?>
Output
A
B
C
SplQueue Object
(
[flags:SplDoublyLinkedList:private] => 4
[dllist:SplDoublyLinkedList:private] => Array
(
[0] => A
[1] => B
[2] => C
)
)
SplQueue Object
(
[flags:SplDoublyLinkedList:private] => 4
[dllist:SplDoublyLinkedList:private] => Array
(
[0] => B
[1] => C
)
)
As was said before, the push () and pop () methods on a SplQueue object, its behave like a stack rather than a queue.
Knowing that the enqueue () and dequeue () methods are respectively aliases of push () and shift () methods, we can also use SplQueue :: push () and SplQueue :: shift () for the same purpose as SplQueue :: enqueue and SplQueue :: dequeue.
Answer to Manu Manjunath post (#114336).
IMO, pop() works as expected.
There are 2 main groups of methods:
1) pop() & push() are inherited from SplDoublyLinkedList and can be applied to SplStack as well as SplQueue (ie are "faceless"). It isn't about stack or queue; it's just about deleting / adding element to the end of the list;
2) the same situation with shift() & unshift(): it is just about adding an element to the beginning of the list, and doesn't matter, if we use it on SplStack or SplQueue.
So, yes, $q->pop(); will remove *last* element from SplQueue $q.
But enqueue() & dequeue() *are about* SplQueue. FIFO principle is realized by these methods, which were implemented *exactly* for queue purpose:
- enqueue() adds an element to the end of the queue and is alias for "faceless" push() (FI...);
- dequeue() removes element from the beginning of the queue and is alias for "faceless" shift() (...FO).
If you want to delete *next in line* element from *queue*, use dequeue().
If you want to delete *last* element from the list (doesn't matter, if it's queue or stack), use pop().