Object oriented coding in a multi threaded request environment - PHP - php

Question

I am writing a web application in an object oriented design. This application would be interacting with the database pretty often. A few regular operations are verifying a user's ACL permissions for the function/method requested, performing certain functions etc. In a nutshell, the database would be used a lot. So my question here is, if I do develop my application using OOP, and declare class level variables which would be used to set the input coming in, and if there is any parallel or concurrent request coming in from another user, would the input data be changed??
Would I have to do something separate to make sure that the application is multi-threaded and the input coming in be not changed until the process isn't finished??
ex:
class myProces{
var $input1;
var $input2;
function process1($ip1, $ip2){
$this->input1 = $ip1;
$this->input2 = $ip2;
$this->getDataDB();
}
function getDataDB(){
//do some database activity with the class level variables;
// I would pass the values in the class level variables;
$query = "select column from table where col1 = $this->input1 and col2= $this->input2";
mysql_query($query);
return something;
}
}
Now if I have two users hitting my application at the same time, and make a call to the functions in this class
user1:
$obj = new myProces();
$obj->process1(1,2);
user2:
$obj = new myProces();
$obj->process1(5,6);
Now if I do have class level variables, would they have changed values when concurrent requests come in?? Would PHP doing any kind of handling for multi threading? I am not sure if Apache can act as a message queue, where requests can be queued.
Can anybody explain if OOP for web applications with heavy number of users is good or if any kind of multithreading has to be done by developers??

Answer 1

A couple of things:
This has nothing to do with OOP.
PHP doesn't support user threads
Each request will be using its own memory, so you don't have to worry about concurrent usage updating variables behind your back.
However, you do have to take care when dealing with data from a database. User 1 may read something, then User 2 may read the same thing and update it before User 1 finishes. Then when User 1 updates it, he may be accidentally overwriting something User 2 did.
These sorts of things can be handled with transactions, locks, etc. Again, it has nothing to do with OOP or multithreading.

Answer 2

First: try to learn about PDO (unless that VAR before the variables, means that you're using PHP4).
Second: As konforce and Grossman said, each user gets differents instances of PHP.
Third: This problem may occur in Java projects (and others), that uses static objects or static methods. Don't worry with this in PHP.

Answer 3

There is no need to worry about mixing things up on the PHP side, but when you come up with a need to update or insert data, having several users being able to modify the same subset of data will lead you into unwanted consequences. Such as inserting duplicate rows or modifying the same row. Thus, you need to use SQL commands such as locking tables or rows.

Answer 4

This isn't a problem you have to worry about. Each connection to your web server spawns a totally separate instance of the PHP interpreter, with totally separate memory and resource handles. No objects in one will be affected by the other, no database connections in one will be affected by the other. Your class properties in one process are not ever modified by a request in another process.
Many of the top sites on the web run on Apache and PHP, with hundreds of concurrent request happening simultaneously all day long, and they do not have to write any special code to handle it.