CascadiaPHP 2024

SplQueue 类

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

简介

SplQueue 类的主要功能是通过将迭代模式设置为 SplDoublyLinkedList::IT_MODE_FIFO 来提供使用双向链表实现的队列。

类摘要

class SplQueue extends SplDoublyLinkedList {
/* 继承的常量 */
/* 方法 */
public dequeue(): mixed
public enqueue(mixed $value): void
/* 继承的方法 */
public SplDoublyLinkedList::add(int $index, mixed $value): void
}

示例

示例 #1 SplQueue 示例

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

以上示例会输出:

1
2
3

示例 #2 使用 SplQueue 高效处理任务

<?php
$q
= new SplQueue();
$q->setIteratorMode(SplQueue::IT_MODE_DELETE);
// ... enqueue some tasks on the queue ...
// process them
foreach ($q as $task) {
// ... process $task ...
// add new tasks on the queue
$q[] = $newTask;
// ...
}
?>

目录

add a note

User Contributed Notes 6 notes

up
52
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
2
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
2
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().
up
0
Stingus
7 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
-2
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.
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