PHP process model per request - Step-by-Step Execution

Concept Flow - PHP process model per request

Client sends HTTP request

↓

Web server receives request

↓

Web server starts PHP process

↓

PHP process initializes environment

↓

PHP executes script from start to end

↓

PHP sends output to web server

↓

Web server sends response to client

↓

PHP process ends and cleans up

Each HTTP request starts a new PHP process that runs the script fully, then ends, sending output back to the client.

Execution Sample

PHP

<?php
// Simple PHP script
echo "Hello, world!";

This script runs once per request, outputs text, then the PHP process ends.

Execution Table

Step	Action	State/Output	Notes
1	Client sends HTTP request	Request received by web server	Start of process
2	Web server starts PHP process	New PHP process created	Isolated environment for this request
3	PHP initializes environment	Variables, settings ready	Fresh start for each request
4	PHP executes script	Outputs 'Hello, world!'	Script runs top to bottom
5	PHP sends output to web server	Output buffered and sent	Response ready for client
6	Web server sends response	Client receives 'Hello, world!'	End user sees output
7	PHP process ends	Memory and resources freed	No state saved for next request

💡 PHP process ends after script execution, no persistent state kept.

Variable Tracker

Variable	Start	After script execution	Final
Output buffer	Empty	"Hello, world!"	Sent and cleared
Memory	Clean	Used during script	Freed after process ends

Key Moments - 3 Insights

Why does PHP start a new process for each request?

Because PHP is designed to run scripts fresh each time, ensuring no leftover data or state from previous requests, as shown in execution_table steps 2 and 7.

Does PHP keep variables or data between requests?

No, each PHP process ends after the request, clearing all variables and memory (see execution_table step 7 and variable_tracker).

What happens to the output generated by PHP?

The output is buffered during script execution and sent to the web server, which then sends it to the client (execution_table steps 4 and 5).

Visual Quiz - 3 Questions

Look at the execution_table, at which step does PHP send the output to the web server?

A Step 5

B Step 4

C Step 6

D Step 7

💡 Hint

Check the 'Action' column in execution_table row 5.

According to variable_tracker, what happens to memory after the PHP process ends?

A Memory is kept for next request

B Memory is freed

C Memory is doubled

D Memory is saved to disk

💡 Hint

Look at the 'Memory' row in variable_tracker, final column.

If PHP did not start a new process per request, what would change in the execution flow?

A Web server would not receive requests

B Output would not be sent

C Step 7 would not free memory

D Client would not send requests

💡 Hint

Consider the importance of process cleanup in execution_table step 7.

Concept Snapshot

PHP process model per request:
- Each HTTP request starts a new PHP process
- PHP runs the script from start to end
- Output is sent to the web server
- Process ends, freeing all memory
- No data persists between requests

Full Transcript

When a client sends an HTTP request, the web server starts a new PHP process. This process initializes a fresh environment and runs the PHP script from top to bottom. The script generates output, which PHP sends back to the web server. The web server then sends this response to the client. After the script finishes, the PHP process ends and frees all memory and variables. This means PHP does not keep any data between requests, ensuring each request is handled independently.

Practice

1. What happens to PHP variables after a web request finishes?

easy

A. They become global variables accessible by all users

B. They keep their values for the next request automatically

C. They are stored permanently in the server memory

D. They are reset and lost unless saved externally

Solution

1. Step 1: Understand PHP request lifecycle

   PHP starts fresh for each request, so variables exist only during that request.

2. Step 2: Identify variable persistence

   Variables reset after request ends unless saved in sessions or databases.

3. Final Answer:

   They are reset and lost unless saved externally -> Option D

4. Quick Check:

   PHP variables reset each request = D [OK]

Hint: Remember: PHP starts fresh every request, no variable memory [OK]

Common Mistakes:

• Thinking variables persist automatically between requests
• Confusing PHP with long-running server processes
• Assuming global variables keep values across users

2. Which PHP code snippet correctly shows the start of a new request process?

easy

A.

B.

C.

D.

Solution

1. Step 1: Analyze variable initialization

   In a new request, variables start fresh; $count = 0 sets it properly.

2. Step 2: Check other options for persistence

   Options A, B, D try to increment without initialization or rely on static/session which need extra setup.

3. Final Answer:

   <?php $count = 0; echo $count; ?> -> Option C

4. Quick Check:

   New request means fresh variables = C [OK]

Hint: Fresh request means variables start from scratch [OK]

Common Mistakes:

• Assuming static variables keep value across requests
• Using session without starting it
• Incrementing uninitialized variables

3. What will be the output of this PHP code when run twice in separate requests?

<?php
session_start();
if (!isset($_SESSION['visits'])) {
  $_SESSION['visits'] = 1;
} else {
  $_SESSION['visits']++;
}
echo $_SESSION['visits'];
?>

medium

A. 1 then 2

B. 1 then 1

C. 2 then 3

D. Error on second request

Solution

1. Step 1: Understand session persistence

   Session data keeps values across requests, so visits count increases.

2. Step 2: Trace two requests

   First request sets visits=1; second request increments to 2.

3. Final Answer:

   1 then 2 -> Option A

4. Quick Check:

   Session stores visits count = 1 then 2 [OK]

Hint: Sessions keep data between requests, variables do not [OK]

Common Mistakes:

• Thinking variables persist without sessions
• Forgetting to call session_start()
• Expecting static variables to persist across requests

4. Identify the error in this PHP code snippet that tries to keep a counter across requests:

<?php
$count = 0;
$count++;
echo $count;
?>

medium

A. Variables reset each request, so counter never increases

B. Syntax error due to missing semicolon

C. Session not started, so counter is undefined

D. Static variable needed to keep count

Solution

1. Step 1: Check variable behavior per request

   $count is set to 0 every time, so increment always starts fresh.

2. Step 2: Identify persistence issue

   Without sessions or external storage, counter resets each request.

3. Final Answer:

   Variables reset each request, so counter never increases -> Option A

4. Quick Check:

   Variables reset each request = A [OK]

Hint: Variables reset each request; use sessions to persist [OK]

Common Mistakes:

• Assuming static variables persist across requests
• Confusing syntax errors with logic errors
• Forgetting to start sessions for persistence

5. You want to count unique visitors to your PHP website. Which approach correctly uses PHP's process model per request to achieve this?

hard

A. Use a static variable in PHP script to count visitors

B. Store visitor count in a database and increment on each request

C. Increment a PHP variable without sessions or storage

D. Rely on PHP variables to keep count across requests

Solution

1. Step 1: Understand PHP process model limits

   PHP variables reset each request, so they can't keep visitor count.

2. Step 2: Identify persistent storage method

   Database stores data permanently and can be updated each request.

3. Final Answer:

   Store visitor count in a database and increment on each request -> Option B

4. Quick Check:

   Persistent storage needed for visitor count = A [OK]

Hint: Use database or sessions to save data beyond request [OK]

Common Mistakes:

• Using static or normal variables expecting persistence
• Ignoring need for external storage
• Confusing sessions with static variables