README

A library for preventing duplicate execution of identical operations in PHP with support for various storage backends (Memory, Redis).

Description

Single Flight is a pattern that ensures the same operation (e.g., database query or external API request) executes only once, even if multiple processes or threads request it simultaneously. Other requests will wait for the result of the first execution.

Key Features

• Prevention of duplicate operations
• Inter-process synchronization
• Support for various storage backends (Memory, Redis)
• TTL (Time To Live) for automatic cache expiration
• Result caching between processes via Redis
• Cache stampede prevention

Installation

composer require xman12/single-flight

Usage

Basic Example (In-Memory)

<?php

use SingleFlight\SingleFlight;

$sf = new SingleFlight();

// This function will execute only once,
// even if do() is called multiple times with the same key
$result = $sf->do('fetch-user-1', function() {
    // Heavy operation (DB query, API call, etc.)
    return fetchUserFromDatabase(1);
});

Using with Redis

<?php

use SingleFlight\SingleFlight;
use SingleFlight\Store\RedisStore;
use Predis\Client;

$redis = new Client([
    'scheme' => 'tcp',
    'host'   => '127.0.0.1',
    'port'   => 6379,
]);

$store = new RedisStore($redis, 'my_app:');
$sf = new SingleFlight($store);

// Result will be cached in Redis and available across processes
$result = $sf->do('expensive-operation', function() {
    return performExpensiveOperation();
});

TTL (Time To Live)

<?php

// Cache with 60 seconds TTL
$result = $sf->do('temp-data', function() {
    return fetchTemporaryData();
}, 30.0, 60); // timeout 30s, TTL 60s

// Or set default TTL
$sf = new SingleFlight($store, null, 300); // 5 minutes by default

Using with Group

<?php

use SingleFlight\Group;
use SingleFlight\Store\RedisStore;

$store = new RedisStore($redis, 'group:');
$group = new Group(null, $store);

[$result, $wasExecuted] = $group->do('expensive-operation', function() {
    return performExpensiveOperation();
});

// $wasExecuted - true if this operation was actually executed,
// false if we got a cached result
if ($wasExecuted) {
    echo "Operation was executed";
} else {
    echo "Got cached result";
}

Cache Clearing

<?php

// Clear specific key
$sf->forget('fetch-user-1');

// Clear everything
$sf->forget();

Cache Stampede Prevention

<?php

use SingleFlight\SingleFlight;
use SingleFlight\Store\RedisStore;

$store = new RedisStore($redis);
$sf = new SingleFlight($store);

// Multiple simultaneous requests
// Only ONE of them will execute the function, the rest will wait for the result
$result = $sf->do('popular-content', function() {
    sleep(5); // Heavy operation
    return fetchPopularContent();
});

Project Structure

src/
├── SingleFlight.php              # Main library class
├── Group.php                     # Class for grouping operations
├── Exception/
│   └── SingleFlightException.php # Library exceptions
└── Store/
    ├── StoreInterface.php        # Interface for storage backends
    ├── MemoryStore.php          # In-memory implementation
    └── RedisStore.php           # Redis implementation

Storage Backends (Stores)

MemoryStore

Stores data in the current process memory. Used by default.

use SingleFlight\Store\MemoryStore;

$store = new MemoryStore();
$sf = new SingleFlight($store);

RedisStore

Stores data in Redis. Allows sharing results between processes.

use SingleFlight\Store\RedisStore;
use Predis\Client;

$redis = new Client('tcp://127.0.0.1:6379');
$store = new RedisStore($redis, 'prefix:'); // prefix is optional
$sf = new SingleFlight($store);

Additional RedisStore Methods:

// Set key expiration time
$store->expire('key', 60);

// Get remaining time to live
$ttl = $store->ttl('key');

// Increment/decrement
$store->increment('counter', 1);
$store->decrement('counter', 1);

Examples

See the examples/ folder for complete usage examples:

• examples/redis_example.php - Working with Redis
• examples/group_redis_example.php - Using Group with Redis

Running examples:

php examples/redis_example.php
php examples/group_redis_example.php

Requirements

• PHP >= 8.1
• Symfony Lock Component >= 6.4
• Predis >= 2.2 (for RedisStore)

Testing

composer install
vendor/bin/phpunit

For Redis tests, make sure Redis is running on 127.0.0.1:6379:

# Run Redis via Docker
docker run -d -p 6379:6379 redis:alpine

# Run tests
vendor/bin/phpunit

API Reference

SingleFlight

// Constructor
public function __construct(
    ?StoreInterface $store = null,      // Storage backend (default MemoryStore)
    ?LockFactory $lockFactory = null,   // Lock factory
    int $defaultTtl = 0                 // Default TTL (0 = no expiration)
)

// Execute operation once
public function do(
    string $key,                        // Unique operation key
    callable $fn,                       // Function to execute
    float $timeout = 30.0,              // Lock timeout
    ?int $ttl = null                    // TTL for result
): mixed

// Check if cache exists
public function has(string $key): bool

// Clear cache
public function forget(?string $key = null): void

// Get storage backend
public function getStore(): StoreInterface

Group

// Constructor
public function __construct(
    ?SingleFlight $singleFlight = null,
    ?StoreInterface $store = null
)

// Execute operation
public function do(
    string $key,
    callable $fn,
    float $timeout = 30.0,
    ?int $ttl = null
): array // [result, wasExecuted]

// Clear cache
public function forget(?string $key = null): void

License

MIT