DurationLimiter.php

TLDR

The DurationLimiter.php file is a part of the Illuminate\Redis\Limiters namespace in the Demo Projects project. It contains a class called DurationLimiter that implements a duration-based limiter for controlling concurrent tasks. The class has several methods to acquire, release, and check the status of the lock.

Methods

__construct($redis, $name, $maxLocks, $decay)

This method is the constructor of the DurationLimiter class. It initializes the properties of the class.

block($timeout, $callback = null, $sleep = 750)

This method attempts to acquire the lock for the given number of seconds. It blocks the execution until the lock is acquired or a timeout occurs. It also provides an optional callback to execute after acquiring the lock.

acquire()

This method attempts to acquire the lock. It uses a Lua script to perform the acquisition logic. If the lock is acquired successfully, it updates the decaysAt and remaining properties accordingly.

tooManyAttempts()

This method determines if the key has been "accessed" too many times within the duration. It uses a Lua script to perform the check and updates the decaysAt and remaining properties.

clear()

This method clears the limiter by deleting the lock key from Redis.

Classes

DurationLimiter

This class implements a duration-based limiter for controlling concurrent tasks. It has methods to acquire, release, and check the status of the lock.

<?php

namespace Illuminate\Redis\Limiters;

use Illuminate\Contracts\Redis\LimiterTimeoutException;
use Illuminate\Support\Sleep;

class DurationLimiter
{
    /**
     * The Redis factory implementation.
     *
     * @var \Illuminate\Redis\Connections\Connection
     */
    private $redis;

    /**
     * The unique name of the lock.
     *
     * @var string
     */
    private $name;

    /**
     * The allowed number of concurrent tasks.
     *
     * @var int
     */
    private $maxLocks;

    /**
     * The number of seconds a slot should be maintained.
     *
     * @var int
     */
    private $decay;

    /**
     * The timestamp of the end of the current duration.
     *
     * @var int
     */
    public $decaysAt;

    /**
     * The number of remaining slots.
     *
     * @var int
     */
    public $remaining;

    /**
     * Create a new duration limiter instance.
     *
     * @param  \Illuminate\Redis\Connections\Connection  $redis
     * @param  string  $name
     * @param  int  $maxLocks
     * @param  int  $decay
     * @return void
     */
    public function __construct($redis, $name, $maxLocks, $decay)
    {
        $this->name = $name;
        $this->decay = $decay;
        $this->redis = $redis;
        $this->maxLocks = $maxLocks;
    }

    /**
     * Attempt to acquire the lock for the given number of seconds.
     *
     * @param  int  $timeout
     * @param  callable|null  $callback
     * @param  int  $sleep
     * @return mixed
     *
     * @throws \Illuminate\Contracts\Redis\LimiterTimeoutException
     */
    public function block($timeout, $callback = null, $sleep = 750)
    {
        $starting = time();

        while (! $this->acquire()) {
            if (time() - $timeout >= $starting) {
                throw new LimiterTimeoutException;
            }

            Sleep::usleep($sleep * 1000);
        }

        if (is_callable($callback)) {
            return $callback();
        }

        return true;
    }

    /**
     * Attempt to acquire the lock.
     *
     * @return bool
     */
    public function acquire()
    {
        $results = $this->redis->eval(
            $this->luaScript(), 1, $this->name, microtime(true), time(), $this->decay, $this->maxLocks
        );

        $this->decaysAt = $results[1];

        $this->remaining = max(0, $results[2]);

        return (bool) $results[0];
    }

    /**
     * Determine if the key has been "accessed" too many times.
     *
     * @return bool
     */
    public function tooManyAttempts()
    {
        [$this->decaysAt, $this->remaining] = $this->redis->eval(
            $this->tooManyAttemptsLuaScript(), 1, $this->name, microtime(true), time(), $this->decay, $this->maxLocks
        );

        return $this->remaining <= 0;
    }

    /**
     * Clear the limiter.
     *
     * @return void
     */
    public function clear()
    {
        $this->redis->del($this->name);
    }

    /**
     * Get the Lua script for acquiring a lock.
     *
     * KEYS[1] - The limiter name
     * ARGV[1] - Current time in microseconds
     * ARGV[2] - Current time in seconds
     * ARGV[3] - Duration of the bucket
     * ARGV[4] - Allowed number of tasks
     *
     * @return string
     */
    protected function luaScript()
    {
        return <<<'LUA'
local function reset()
    redis.call('HMSET', KEYS[1], 'start', ARGV[2], 'end', ARGV[2] + ARGV[3], 'count', 1)
    return redis.call('EXPIRE', KEYS[1], ARGV[3] * 2)
end

if redis.call('EXISTS', KEYS[1]) == 0 then
    return {reset(), ARGV[2] + ARGV[3], ARGV[4] - 1}
end

if ARGV[1] >= redis.call('HGET', KEYS[1], 'start') and ARGV[1] <= redis.call('HGET', KEYS[1], 'end') then
    return {
        tonumber(redis.call('HINCRBY', KEYS[1], 'count', 1)) <= tonumber(ARGV[4]),
        redis.call('HGET', KEYS[1], 'end'),
        ARGV[4] - redis.call('HGET', KEYS[1], 'count')
    }
end

return {reset(), ARGV[2] + ARGV[3], ARGV[4] - 1}
LUA;
    }

    /**
     * Get the Lua script to determine if the key has been "accessed" too many times.
     *
     * KEYS[1] - The limiter name
     * ARGV[1] - Current time in microseconds
     * ARGV[2] - Current time in seconds
     * ARGV[3] - Duration of the bucket
     * ARGV[4] - Allowed number of tasks
     *
     * @return string
     */
    protected function tooManyAttemptsLuaScript()
    {
        return <<<'LUA'

if redis.call('EXISTS', KEYS[1]) == 0 then
    return {0, ARGV[2] + ARGV[3]}
end

if ARGV[1] >= redis.call('HGET', KEYS[1], 'start') and ARGV[1] <= redis.call('HGET', KEYS[1], 'end') then
    return {
        redis.call('HGET', KEYS[1], 'end'),
        ARGV[4] - redis.call('HGET', KEYS[1], 'count')
    }
end

return {0, ARGV[2] + ARGV[3]}
LUA;
    }
}