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<?php
namespace malkusch\lock\mutex;
use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
use Psr\Log\LoggerAwareInterface;
use malkusch\lock\exception\LockAcquireException;
use malkusch\lock\exception\LockReleaseException;
/**
* Mutex based on the Redlock algorithm.
*
* @author Markus Malkusch <[email protected]>
* @license WTFPL
*
* @link http://redis.io/topics/distlock
* @link bitcoin:1P5FAZ4QhXCuwYPnLZdk3PJsqePbu1UDDA Donations
*/
abstract class RedisMutex extends SpinlockMutex implements LoggerAwareInterface
{
/**
* @var string The random value token for key identification.
*/
private $token;
/**
* @var array The Redis APIs.
*/
private $redisAPIs;
/**
* @var LoggerInterface The logger.
*/
private $logger;
/**
* Sets the Redis APIs.
*
* @param array $redisAPIs The Redis APIs.
* @param string $name The lock name.
* @param int $timeout The time in seconds a lock expires, default is 3.
*
* @throws \LengthException The timeout must be greater than 0.
*/
public function __construct(array $redisAPIs, $name, $timeout = 3)
{
parent::__construct($name, $timeout);
$this->redisAPIs = $redisAPIs;
$this->logger = new NullLogger();
}
/**
* Sets a logger instance on the object
*
* RedLock is a fault tolerant lock algorithm. I.e. it does tolerate
* failing redis connections without breaking. If you want to get notified
* about such events you'll have to provide a logger. Those events will
* be logged as warnings.
*
* @param LoggerInterface $logger The logger.
*/
public function setLogger(LoggerInterface $logger)
{
$this->logger = $logger;
}
/**
* @SuppressWarnings(PHPMD)
* @internal
*/
protected function acquire($key, $expire)
{
// 1. This differs from the specification to avoid an overflow on 32-Bit systems.
$time = microtime(true);
// 2.
$acquired = 0;
$errored = 0;
$this->token = \random_int(0, 2147483647);
$exception = null;
foreach ($this->redisAPIs as $redis) {
try {
if ($this->add($redis, $key, $this->token, $expire)) {
$acquired++;
}
} catch (LockAcquireException $exception) {
$context = [
"key" => $key,
"token" => $this->token,
"redis" => $this->getRedisIdentifier($redis),
"exception" => $exception
];
$this->logger->warning("Could not set {key} = {token} at {redis}.", $context);
$errored++;
}
}
// 3.
$elapsedTime = microtime(true) - $time;
$isAcquired = $this->isMajority($acquired) && $elapsedTime <= $expire;
if ($isAcquired) {
// 4.
return true;
}
// 5.
$this->release($key);
// In addition to RedLock it's an exception if too many servers fail.
if (!$this->isMajority(count($this->redisAPIs) - $errored)) {
assert(!is_null($exception)); // The last exception for some context.
throw new LockAcquireException(
"It's not possible to acquire a lock because at least half of the Redis server are not available.",
LockAcquireException::REDIS_NOT_ENOUGH_SERVERS,
$exception
);
}
return false;
}
/**
* @internal
*/
protected function release($key)
{
/*
* Question for Redis: Why do I have to try to delete also keys
* which I haven't acquired? I do observe collisions of the random
* token, which results in releasing the wrong key.
*/
/*
* All Redis commands must be analyzed before execution to determine which keys the command will operate on. In
* order for this to be true for EVAL, keys must be passed explicitly.
*/
$script = '
if redis.call("get",KEYS[1]) == ARGV[1] then
return redis.call("del",KEYS[1])
else
return 0
end
';
$released = 0;
foreach ($this->redisAPIs as $redis) {
try {
if ($this->evalScript($redis, $script, 1, [$key, $this->token])) {
$released++;
}
} catch (LockReleaseException $e) {
$context = [
"key" => $key,
"token" => $this->token,
"redis" => $this->getRedisIdentifier($redis),
"exception" => $e
];
$this->logger->warning("Could not unset {key} = {token} at {redis}.", $context);
}
}
return $this->isMajority($released);
}
/**
* Returns if a count is the majority of all servers.
*
* @param int $count The count.
* @return bool True if the count is the majority.
*/
private function isMajority($count)
{
return $count > count($this->redisAPIs) / 2;
}
/**
* Sets the key only if such key doesn't exist at the server yet.
*
* @param mixed $redisAPI The connected Redis API.
* @param string $key The key.
* @param string $value The value.
* @param int $expire The TTL seconds.
*
* @return bool True, if the key was set.
* @throws LockAcquireException An unexpected error happened.
* @internal
*/
abstract protected function add($redisAPI, $key, $value, $expire);
/**
* @param mixed $redisAPI The connected Redis API.
* @param string $script The Lua script.
* @param int $numkeys The number of values in $arguments that represent Redis key names.
* @param array $arguments Keys and values.
*
* @return mixed The script result, or false if executing failed.
* @throws LockReleaseException An unexpected error happened.
* @internal
*/
abstract protected function evalScript($redisAPI, $script, $numkeys, array $arguments);
/**
* Returns a string representation of the Redis API.
*
* @param mixed $redisAPI The connected Redis API.
* @return string The identifier.
* @internal
*/
abstract protected function getRedisIdentifier($redisAPI);
}