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);//返回true代表加锁成功,返回false代表加锁失败
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
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