Implement Non-Blocking Session in PHP

As we all know Session is the most important component in the web application. Before describing the non-blocking session, I would like too little introduce about PHP Session. The session is the way to store data for each user against a unique session ID. By default, session usages file to storing the session data. When session_start() is called then PHP creates a unique identifier number for that particular session. And sent that number to users browser to save that number. Contiguous create a new file with the same name of the unique identification number. And browser will use that unique identification number to communicate with that server. To know more about How Does PHP Session Works read this article.

Non-Blocking Session

What Does Session Locking:

When web server getting the concurrent request which involves with PHP Session. Then the first request will engage the Session file to work with it and locked that Session file. And rest of the request who also have to engage with Session, they will be blocked (waiting for the unlock of the Session file). When the first request did its activities then release the Session file and then the second request will engage with The session. And this happened until the last request is served. This is actually called Session Looking. To understand more about Session Locking read this article.

Non-Blocking Session:

To improve the application performance we need to avoid this problem. To avoid the PHP Session blocking we can start the session and then close the session. This will unlock the session file and allow the remaining requests to engage with Session, even before the previous request has served.

session_write_close(); function need to call to close the session.

This trick works great if you do not need to read anything in session while your another process is engaged with the session. With this technique, you still able to read the $_SESSION data while the session is engaged with another request.

Example Script:

// start the session
session_start();
// read/write to session
$_SESSION['login_time'] = time();
// close the session
session_write_close();
// now do my long-running code.
// still able to read from session, but not write
$twitterId = $_SESSION['userId'];

How Does PHP Session Works

Basically, the session is the system or way to store information for individual users. It’s storing individual users information against a unique session ID. So in this way, user’s data can be accessible across all pages of a website. PHP follow simple workflow for manage┬ásession, and that is when a session is started, then PHP either retrieve existing session or create a new session. If PHPSESSID is passed then PHP retrieved existing session otherwise creates a new session

By default, session creates a file in a temporary directory (which determined in php.ini file) on a server. All all the variables & value are stored there.

How Does PHP Session Works

How is Works:

  • Firstly PHP creates a unique identifier number (a random string of 32 hexadecimal number, e.g 3c7foj34c3jj973hjkop2fc937e3443) for an individual session.
  • PHPSESSID cookie passes that unique identification number to users’ browser to save that number.
  • A new file is created on the server with the same name of unique identification number with sess_ prefix (ie sess_3c7foj34c3jj973hjkop2fc937e3443.)
  • The browser sends that cookie to the server with each request.
  • If PHP gets that unique identification number from PHPSESSID cookie (on each request), then PHP searches in the temporary directory and compares that number to the file name. If both are the same, then it retrieves the existing session, otherwise it creates a new session for that user.

A session gets destroyed when the user closes the browser or leaves the site. The server also terminates the session after the predetermined period of session time expires. These are the simple mechanism steps that PHP is using to handle the session. I hope this article with help you to understand how PHP SESSION is working.