释放双眼，带上耳机，听听看~！
简介
多线程多进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
基于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
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2$redis->connect('127.0.0.1', 6380);
3$rs = $redis->set('testnx', 123, ['nx', 'ex' => 10]);
4var_dump($rs);//返回true代表加锁成功，返回false代表加锁失败
5
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
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2{
3 private $retryDelay;
4 private $retryCount;
5 private $clockDriftFactor = 0.01;
6 private $quorum;
7 private $servers = array();
8 private $instances = array();
9 function __construct(array $servers, $retryDelay = 200, $retryCount = 3)
10 {
11 $this->servers = $servers;
12 $this->retryDelay = $retryDelay;
13 $this->retryCount = $retryCount;
14 $this->quorum = min(count($servers), (count($servers) / 2 + 1));
15 }
16 public function lock($resource, $ttl)
17 {
18 $this->initInstances();
19 $token = uniqid();
20 $retry = $this->retryCount;
21 do {
22 $n = 0;
23 $startTime = microtime(true) * 1000;
24 foreach ($this->instances as $instance) {
25 if ($this->lockInstance($instance, $resource, $token, $ttl)) {
26 $n++;
27 }
28 }
29 # Add 2 milliseconds to the drift to account for Redis expires
30 # precision, which is 1 millisecond, plus 1 millisecond min drift
31 # for small TTLs.
32 $drift = ($ttl * $this->clockDriftFactor) + 2;
33 $validityTime = $ttl - (microtime(true) * 1000 - $startTime) - $drift;
34 if ($n >= $this->quorum && $validityTime > 0) {
35 return [
36 'validity' => $validityTime,
37 'resource' => $resource,
38 'token' => $token,
39 ];
40 } else {
41 foreach ($this->instances as $instance) {
42 $this->unlockInstance($instance, $resource, $token);
43 }
44 }
45 // Wait a random delay before to retry
46 $delay = mt_rand(floor($this->retryDelay / 2), $this->retryDelay);
47 usleep($delay * 1000);
48 $retry--;
49 } while ($retry > 0);
50 return false;
51 }
52 public function unlock(array $lock)
53 {
54 $this->initInstances();
55 $resource = $lock['resource'];
56 $token = $lock['token'];
57 foreach ($this->instances as $instance) {
58 $this->unlockInstance($instance, $resource, $token);
59 }
60 }
61 private function initInstances()
62 {
63 if (empty($this->instances)) {
64 foreach ($this->servers as $server) {
65 list($host, $port, $timeout) = $server;
66 $redis = new \Redis();
67 $redis->connect($host, $port, $timeout);
68 $this->instances[] = $redis;
69 }
70 }
71 }
72 private function lockInstance($instance, $resource, $token, $ttl)
73 {
74 return $instance->set($resource, $token, ['NX', 'PX' => $ttl]);
75 }
76 private function unlockInstance($instance, $resource, $token)
77 {
78 $script = '
79 if redis.call("GET", KEYS[1]) == ARGV[1] then
80 return redis.call("DEL", KEYS[1])
81 else
82 return 0
83 end
84 ';
85 return $instance->eval($script, [$resource, $token], 1);
86 }
87}
88
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91$servers = [
92 ['127.0.0.1', 6379, 0.01],
93];
94$redLock = new RedLock($servers);
95while (true) {
96 $lock = $redLock->lock('test', 10000);
97 if ($lock) {
98 print_r($lock);
99 $redLock->unlock(['resource' => 'test', 'token' => '5d1c123121538']);
100 } else {
101 print "Lock not acquired\n";
102 }
103}
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后续
Redis分布式锁还有没有问题？
解决方法：引入版本号
