The use of heap and stack in php

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1. About heap and stack Concepts and differences

#Here is a reference to the previous blog: A brief discussion of the difference between heap and stack
Through this article, we can know what heap and stack are in the broad sense. , but what about its specific use in php

2. Stack in php

As we all know, PHP provides a set of functions that can be used for push and pop (stack) as well as shift and unshift ( Queue) to operate on array elements.

1. push and pop

These two functions operate on the stack and follow the first-in, last-out principle. It's like adding something to a barrel. The push operation is performed through array_push, and the pop operation is performed through array_pop. 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) Example:

 <?php
   $arr = array();
   array_push($arr,&#39;aaa&#39;);  //先入栈  aaa
   array_push($arr,&#39;bbb&#39;);  //后入栈   bbb
   print_r($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?>

3. Queue implemented in PHP

1. What is a queue

First of all, it should be clear that queues and ordinary The stack is different, and the queue follows "first in, first out". The stack can only be deleted and inserted at the top of the stack. The queue is that every newly inserted element is inserted at the end of the queue, and every 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 move towards Advance one position, and when the element moves to the head of the queue, it will accept the dequeue operation.

The queue model can be understood as queuing up to eat. The first person in line gets to eat first.

2. Queue operations

Use array_push() in php 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

Detailed reference manual: http://www.w3school.com.cn/php/func_array_shift.asp

(2) Example:

<?php
   $arr = array();
   array_push($arr,&#39;aaa&#39;);  //队列中添加  aaa
   array_push($arr,&#39;bbb&#39;);  // 队列中添加   bbb
   print_r($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 queue, with both ends Insertion and deletion operations are allowed. 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. Generally through PHP's array functions: array_unshift() and array_shift().

Specific reference: PHP queue principle and queue-based file writing case

4. The purpose of queue

Queues can handle data transmission and storage asynchronously. When you If you frequently insert data into the database and frequently submit data to the search engine, you can use a queue to insert asynchronously. In addition, slower processing logic and processing logic with a limited number of concurrency can also be placed in the background for processing through the message queue, such as FLV video conversion, sending mobile phone text messages, sending emails, etc.

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