Класс SplQueue

    (PHP 5 >= 5.3.0, PHP 7, PHP 8)

    Введение

    Класс SplQueue предоставляет основные функциональные возможности очереди, реализованной с использованием двусвязного списка, установив режим итератора SplDoublyLinkedList::IT_MODE_FIFO.

    Обзор класса

    class SplQueue extends SplDoublyLinkedList {
    /* Наследуемые константы */
    public const int SplDoublyLinkedList::IT_MODE_LIFO;
    public const int SplDoublyLinkedList::IT_MODE_FIFO;
    public const int SplDoublyLinkedList::IT_MODE_DELETE;
    public const int SplDoublyLinkedList::IT_MODE_KEEP;
    /* Методы */
    public dequeue(): mixed
    public enqueue(mixed $value): void
    /* Наследуемые методы */
    public SplDoublyLinkedList::add(int $index, mixed $value): void
    public SplDoublyLinkedList::bottom(): mixed
    public SplDoublyLinkedList::count(): int
    public SplDoublyLinkedList::current(): mixed
    public SplDoublyLinkedList::getIteratorMode(): int
    public SplDoublyLinkedList::isEmpty(): bool
    public SplDoublyLinkedList::key(): int
    public SplDoublyLinkedList::next(): void
    public SplDoublyLinkedList::offsetExists(int $index): bool
    public SplDoublyLinkedList::offsetGet(int $index): mixed
    public SplDoublyLinkedList::offsetSet(?int $index, mixed $value): void
    public SplDoublyLinkedList::offsetUnset(int $index): void
    public SplDoublyLinkedList::pop(): mixed
    public SplDoublyLinkedList::prev(): void
    public SplDoublyLinkedList::push(mixed $value): void
    public SplDoublyLinkedList::rewind(): void
    public SplDoublyLinkedList::serialize(): string
    public SplDoublyLinkedList::setIteratorMode(int $mode): int
    public SplDoublyLinkedList::shift(): mixed
    public SplDoublyLinkedList::top(): mixed
    public SplDoublyLinkedList::unserialize(string $data): void
    public SplDoublyLinkedList::unshift(mixed $value): void
    public SplDoublyLinkedList::valid(): bool
    }

    Примеры

    Пример #1 Пример использования SplQueue

    <?php
    $q     = new SplQueue();
    $q[] = 1;
    $q[] = 2;
    $q[] = 3;
    foreach (    $q as $elem) {
    echo     $elem."\n";
    }
    ?>

    Результат выполнения приведённого примера: 

    1
2
3

    Пример #2 Эффективное решение задач с помощью SplQueue

    <?php
    $q     = new SplQueue();
    $q->setIteratorMode(SplQueue::IT_MODE_DELETE);
    // ... добавление некоторых задач в очередь ...
    // обработка
    foreach ($q as $task) {
    // ... обработка $task ...
    // добавление новых задач в очередь
    $q[] = $newTask;
    // ...
    }
    ?>

    Содержание

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    Примечания пользователей 6 notes

    up
    43
    Manu Manjunath
    10 years ago
    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().
    up
    1
    mostefa dot medjahed dot pro at gmail dot com
    3 years ago
    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.
    up
    3
    MrStonedOne
    9 years ago
    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;
    }
    }
    }
    ?>
    up
    1
    lincoln dot du dot j at gmail dot com
    7 years ago
    <?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
    )

    )
    up
    1
    Stingus
    8 years ago
    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
    up
    1
    booleantype at ya dot ru
    3 years ago
    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().
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