README

A PHP implementation of the stale-while-revalidate caching pattern for WordPress, designed to improve performance and reduce load on expensive operations.

Inspired by the recent implementation of Cache::flexible() in Laravel.

Features

• Stale-While-Revalidate Pattern: Serves stale content while asynchronously refreshing cache in the background
• Race Condition Prevention: Uses locking mechanism to prevent multiple simultaneous cache updates
• WordPress Integration: Built on WordPress transients for reliable cache storage
• Async Updates: Leverages FastCGI finish request for non-blocking cache updates (for when using PHP-FPM)
• Type Safety: Written in strict PHP with full type declarations

Installation

composer require ryanhellyer/stale-cache

Usage

Basic usage example:

$result = StaleCache::get(
    'my_cache_key',
    [
        5,      // Stale time in seconds
        3600,   // Cache duration in seconds
        60      // Lock duration in seconds (optional)
    ],
    function() {
        // Your expensive operation here
        return getExpensiveData();
    }
);

Configuration Parameters

• Stale Time: How long the cache is considered fresh (in seconds)
• Cache Duration: Total time to keep the cache (in seconds)
• Lock Duration: How long to hold the refresh lock (defaults to 1 hour)

Cache States

The cache can be in one of three states:

1. Fresh: Content is served directly from cache
2. Stale: Content is served from cache while a background refresh is triggered
3. Missing: Content is generated synchronously and cached

Performance Considerations

• Uses fastcgi_finish_request() when available for non-blocking updates
• Implements locking to prevent cache stampede
• Serves stale content rather than blocking on regeneration

Development

Code Style & Quality

This project follows PSR-12 coding standards and uses several tools to maintain code quality:

PHP CodeSniffer

Check coding standards:

composer phpcs

Automatically fix coding standards violations:

composer phpcs-fix

PHPStan

Run static analysis:

composer phpstan

The project uses PHPStan Level 8 (maximum) for strict type checking and analysis.

Testing

Run the test suite:

composer test

License

This project is licensed under the GPL v2 license.