Cleans up session records whose lifetime has expired.
Before using it, identify which data, connection or runtime state the operation reads or changes. This avoids examples that appear to work but apply to a different context.
What Is SessionHandler::gc() in PHP?
Cleans up session records whose lifetime has expired.
Syntax:
<?php
// Signature for reference only
SessionHandler->gc(int $max_lifetime)
Parameters and Return Value
$max_lifetime— Required int argument supplied to this operation.
Inspect the documented return value and handle the possibility of failure.
Example 1: Basic Usage
<?php
class ObservedSessionHandler extends SessionHandler {
public function gc(int $maximumLifetime): int|false {
// PHP calls this callback at the relevant session lifecycle event.
return parent::gc($maximumLifetime);
}
}
session_set_save_handler(new ObservedSessionHandler(), true);
session_start();
$_SESSION["example"] = "active";
session_write_close();Cleans up session records whose lifetime has expired.
Example 2: Another Case
<?php
class ObservedSessionHandler extends SessionHandler {
public function gc(int $maximumLifetime): int|false {
// PHP calls this callback at the relevant session lifecycle event.
return parent::gc($maximumLifetime);
}
}
session_set_save_handler(new ObservedSessionHandler(), true);
session_start();
$_SESSION["counter"] = ($_SESSION["counter"] ?? 0) + 1;
session_write_close();The second sample illustrates a different way to inspect or handle this operation. Configure the underlying session, socket, key material or connection first.
Practical Example
<?php
class ObservedSessionHandler extends SessionHandler {
public function gc(int $maximumLifetime): int|false {
// PHP calls this callback at the relevant session lifecycle event.
return parent::gc($maximumLifetime);
}
}
session_set_save_handler(new ObservedSessionHandler(), true);
session_start();
$_SESSION["report"] = "complete";
session_write_close();The practical example is a teaching scenario. Change sample configuration and credentials before using a similar design in an application.
Important Behavior and Edge Cases
- Call session configuration functions before starting a session or sending headers; protect identifiers from exposure.
- Relevant PHP environment: session. Ensure the required extension and operating-system capabilities are present.
- Check results and release resources where necessary; successful syntax alone does not guarantee a successful operation.
Comparison With Related Functions
| Option | When to Use It |
|---|---|
SessionHandler::gc | Cleans up session records whose lifetime has expired. |
session_start | Use this related operation for its different responsibilities; do not assume identical inputs or return values. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| Starting the session after response output | Configure cookie flags and session handling before sending body bytes. |
| Assuming session_destroy() removes the browser cookie | Clear session data and expire the cookie using matching scope settings. |
| Keeping the same session ID after authentication | Rotate the identifier when privileges change and use strict mode. |
Key Takeaways
- Cleans up session records whose lifetime has expired.
- Call session configuration functions before starting a session or sending headers; protect identifiers from exposure.
- Validate inputs and handle failure conditions before integrating this operation into a production workflow.
Cleans up session records whose lifetime has expired. Use the appropriate runtime and treat any environment-dependent output as an example, not a guaranteed result.