Question

In an app written in PHP (e.g., a social network), let’s say that 10 users (signed-in) are browsing the website.

In PHP code, there is “user” object created to store users data and to pass values to other functions and classes.

Question: When these 10 users go to user.php, which has code to create “user” object, how are these objects stored in memory in PHP? Do they not conflict? Is each one of the “user” objects are uniquely stored in the memory or would one be overwritten by another?

For example, user a visits first so object “user” contains his/her data but when user second visits, the “user” object in memory is overwritten so when first user calls the object, it’s the second users data retrieved.

Or, is it unique?

I want to understand object in PHP as a newbie, please explain it simply because none of the web pages I found regarding OOP explains this.

Answer 1

PHP is a CGI application, that means, it’s being started and terminated on each request.

• a client sends a request to the web server
• the server starts PHP and passes the request to it
• PHP allocates a chunk of memory for your script
• your script is being executed, all objects it creates are stored in that chunk of memory
• you script generates some html, this html is sent to the client
• the memory is being freed and PHP is stopped

If you have 10 clients requests coming at the same time, 10 copies of php will be started and 10 independent memory chunks will be used. So, no, objects from different requests do not interfere.

(Note: this explanation is deliberately simplified, there are actually different php setups and persistence options).