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<?php
namespace Illuminate\Redis\Limiters;
use Illuminate\Contracts\Redis\LimiterTimeoutException;
use Illuminate\Support\Str;
use Throwable;
class ConcurrencyLimiter
{
/**
* The Redis factory implementation.
*
* @var \Illuminate\Redis\Connections\Connection
*/
protected $redis;
/**
* The name of the limiter.
*
* @var string
*/
protected $name;
/**
* The allowed number of concurrent tasks.
*
* @var int
*/
protected $maxLocks;
/**
* The number of seconds a slot should be maintained.
*
* @var int
*/
protected $releaseAfter;
/**
* Create a new concurrency limiter instance.
*
* @param \Illuminate\Redis\Connections\Connection $redis
* @param string $name
* @param int $maxLocks
* @param int $releaseAfter
* @return void
*/
public function __construct($redis, $name, $maxLocks, $releaseAfter)
{
$this->name = $name;
$this->redis = $redis;
$this->maxLocks = $maxLocks;
$this->releaseAfter = $releaseAfter;
}
/**
* Attempt to acquire the lock for the given number of seconds.
*
* @param int $timeout
* @param callable|null $callback
* @return bool
*
* @throws \Illuminate\Contracts\Redis\LimiterTimeoutException
* @throws \Throwable
*/
public function block($timeout, $callback = null)
{
$starting = time();
$id = Str::random(20);
while (! $slot = $this->acquire($id)) {
if (time() - $timeout >= $starting) {
throw new LimiterTimeoutException;
}
usleep(250 * 1000);
}
if (is_callable($callback)) {
try {
return tap($callback(), function () use ($slot, $id) {
$this->release($slot, $id);
});
} catch (Throwable $exception) {
$this->release($slot, $id);
throw $exception;
}
}
return true;
}
/**
* Attempt to acquire the lock.
*
* @param string $id A unique identifier for this lock
* @return mixed
*/
protected function acquire($id)
{
$slots = array_map(function ($i) {
return $this->name.$i;
}, range(1, $this->maxLocks));
return $this->redis->eval(...array_merge(
[$this->lockScript(), count($slots)],
array_merge($slots, [$this->name, $this->releaseAfter, $id])
));
}
/**
* Get the Lua script for acquiring a lock.
*
* KEYS - The keys that represent available slots
* ARGV[1] - The limiter name
* ARGV[2] - The number of seconds the slot should be reserved
* ARGV[3] - The unique identifier for this lock
*
* @return string
*/
protected function lockScript()
{
return <<<'LUA'
for index, value in pairs(redis.call('mget', unpack(KEYS))) do
if not value then
redis.call('set', KEYS[index], ARGV[3], "EX", ARGV[2])
return ARGV[1]..index
end
end
LUA;
}
/**
* Release the lock.
*
* @param string $key
* @param string $id
* @return void
*/
protected function release($key, $id)
{
$this->redis->eval($this->releaseScript(), 1, $key, $id);
}
/**
* Get the Lua script to atomically release a lock.
*
* KEYS[1] - The name of the lock
* ARGV[1] - The unique identifier for this lock
*
* @return string
*/
protected function releaseScript()
{
return <<<'LUA'
if redis.call('get', KEYS[1]) == ARGV[1]
then
return redis.call('del', KEYS[1])
else
return 0
end
LUA;
}
}