First, the concept and difference between heap and stack
Refer to the previous blog here: Talking about the difference between heap and stack
Through this article, we can know what the generalized heap and stack are, but what about the specific use in php
Second, the stack in php
As we all know, PHP provides a set of functions that can be used to push and pop (stack) and shift and unshift (queue) to manipulate array elements.
1, push and pop
These two functions operate on the stack and follow the principle of first in, last out. It's like adding something to a barrel. The push operation is performed by array_push, and the pop operation is performed by array_pop. The part of the advanced stack is at the bottom of the barrel.
(1) array_push() method
array_push() 函数向第一个参数的数组尾部添加一个或多个元素（入栈），然后返回新数组的长度。该函数等于多次调用 $array[] = $value。
(2) array_pop() method
array_pop() 函数删除数组中的最后一个元素。
返回数组的最后一个值。如果数组是空的，或者非数组，将返回 NULL。
(3) Examples:
<?php
$arr = array();
array_push($arr,'aaa'); //先入栈 aaa
array_push($arr,'bbb'); //后入栈 bbb
print_r($arr); //此时打印结果为：[0]=>aaa,[1]=>bbb
$arr.pop(); //进行出栈操作，先进后出原则，则此时相当于bbb出栈了。
print_r($arr); //打印结果应该是[0]=>aaa
?>Third, the queue implemented by php
1. What is a queue
First of all, it should be clear that queues are different from ordinary stacks, and queues follow "first-in, first-out". The stack can only be deleted and inserted at the top of the stack. The queue is that each newly inserted element is inserted at the end of the queue, and each element to be deleted is located at the head of the queue. When an element is deleted from the head of the queue, the elements in other queues will be sent to the queue. Advance 1 bit, when the element moves to the head of the queue, it will accept the dequeue operation.
The queue model can be understood as queuing for meals. The first person to line up gets the meal first.
2, the operation of the queue
In PHP, use array_push() to add elements and use array_shift() to delete elements.
(1) array_shift() method
array_shift() 函数删除数组中第一个元素，并返回被删除元素的值。
如果键名是数字的，所有元素都会获得新的键名，从 0 开始，并以 1 递增
Specific reference manual: http://www.w3school.com.cn/php/func_array_shift.asp
(2) Examples:
<?php
$arr = array();
array_push($arr,'aaa'); //队列中添加 aaa
array_push($arr,'bbb'); // 队列中添加 bbb
print_r($arr); //此时打印输出为 [0]=>aaa,[1]=>bbb
array_shift($arr); //删除第一个元素，遵循先进先出原则，删除的是aaa
print_r($arr); //打印结果为 [0]=>bbb
?>(3) Double-ended queue
There is also a special kind of queue that allows insertion and deletion operations at both ends. This kind of queue can be called a double-ended queue. The difference from the standard queue is that there are more insertion operations at the head of the queue and deletion operations at the tail of the queue. Usually through php's array functions: array_unshift() and array_shift().
Specific reference: PHP queue principle and queue-based file writing case
Fourth, the use of the queue
Queues can handle data transmission and storage asynchronously very well. When you frequently insert data into the database and submit data to search engines frequently, you can use queues for asynchronous insertion. In addition, slower processing logic and processing logic with a limited number of concurrency can also be placed in the background for processing through message queues, such as FLV video conversion, sending mobile phone short messages, sending emails, and so on.
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