简介
多线程情况下访问一些共享资源需要加锁，否则就会导致数据错乱的问题
分布式锁可以通过DB，Redis，Zk等方式实现，本节主要介绍php使用Redis实现分布式锁
set命令
setnx key value 设置一个值，当key已经存在时，返回flase，代表失败
使用setnx实现分布锁有个缺陷，setnx操作无法设置key的ttl，需要配合exprie key ttl 一起使用
好在set命令就集成了nx和ex操作set key name NX PX 10000
$redis = new Redis();$redis->connect('127.0.0.1', 6380);$rs = $redis->set('testnx', 123, ['nx', 'ex' => 10]);var_dump($rs);Redlock
set命令还有一个问题，当你要提前释放这个锁的时候，使用expire key 0或者使用del key
如果expire或者del命令发送了阻塞，锁自动失效，这时候B获取了锁，expire/del命令到达，导致B获取的锁失效
Redlock在加锁的时候value值要保证唯一性，在释放锁的时候要验证value是否和申请锁时value是否一致
class RedLock{ private $retryDelay; private $retryCount; private $clockDriftFactor = 0.01; private $quorum; private $servers = array(); private $instances = array(); function __construct(array $servers, $retryDelay = 200, $retryCount = 3) { $this->servers = $servers; $this->retryDelay = $retryDelay; $this->retryCount = $retryCount; $this->quorum = min(count($servers), (count($servers) / 2 + 1)); } public function lock($resource, $ttl) { $this->initInstances(); $token = uniqid(); $retry = $this->retryCount; do { $n = 0; $startTime = microtime(true) * 1000; foreach ($this->instances as $instance) { if ($this->lockInstance($instance, $resource, $token, $ttl)) { $n++; } } # Add 2 milliseconds to the drift to account for Redis expires # precision, which is 1 millisecond, plus 1 millisecond min drift # for small TTLs. $drift = ($ttl * $this->clockDriftFactor) + 2; $validityTime = $ttl - (microtime(true) * 1000 - $startTime) - $drift; if ($n >= $this->quorum && $validityTime > 0) { return [ 'validity' => $validityTime, 'resource' => $resource, 'token' => $token, ]; } else { foreach ($this->instances as $instance) { $this->unlockInstance($instance, $resource, $token); } } // Wait a random delay before to retry $delay = mt_rand(floor($this->retryDelay / 2), $this->retryDelay); usleep($delay * 1000); $retry--; } while ($retry > 0); return false; } public function unlock(array $lock) { $this->initInstances(); $resource = $lock['resource']; $token = $lock['token']; foreach ($this->instances as $instance) { $this->unlockInstance($instance, $resource, $token); } } private function initInstances() { if (empty($this->instances)) { foreach ($this->servers as $server) { list($host, $port, $timeout) = $server; $redis = new \Redis(); $redis->connect($host, $port, $timeout); $this->instances[] = $redis; } } } private function lockInstance($instance, $resource, $token, $ttl) { return $instance->set($resource, $token, ['NX', 'PX' => $ttl]); } private function unlockInstance($instance, $resource, $token) { $script = ' if redis.call("GET", KEYS[1]) == ARGV[1] then return redis.call("DEL", KEYS[1]) else return 0 end '; return $instance->eval($script, [$resource, $token], 1); }}$servers = [ ['127.0.0.1', 6379, 0.01],];$redLock = new RedLock($servers);while (true) { $lock = $redLock->lock('test', 10000); if ($lock) { print_r($lock); $redLock->unlock(['resource' => 'test', 'token' => '5d1c123121538']); } else { print "Lock not acquired\n"; }}后续
Redis分布式锁还有没有问题？
解决方法：引入版本号
参考：https://time.geekbang.org/col...