悲观锁

• select * from Post where id= for update

乐观锁

• Entity::version
• update Post set content='...', version=version+1 where version= and id=

php lock

• symfony.com/doc/current…

分布式锁

• redis.io/commands/se…
• redis.io/commands/de…
• redis.io/commands/ev…
  • set/del

  SET resource-name anystring NX EX max-lock-time
  DEL resource-name
  

  • Instead of setting a fixed string, set a non-guessable large random string, called token.
  • Instead of releasing the lock with DEL, send a script that only removes the key if the value matches.
  • lua

  if redis.call("get",KEYS[1]) == ARGV[1] then
      return redis.call("del",KEYS[1])
  else
      return 0
  end
  

• redis.io/topics/dist…
• juejin.cn/book/701839…

Symfony::Doctrine 集成解决方案

• 锁实现
  • symfony.com/doc/current…
  • 自己实现 redis.io/commands/se…
  • random_value
    • packagist.org/packages/ra…
    • packagist.org/packages/sy…
    • www.php.net/manual/en/f…
• 集成入 EntityManager

class EntityManagerXieLock
{
  private $em = null;
  private $lockFactory = null;
  private $locks = [];

  public function __construct(EntityManager $em, LockFactory $lockFactory)
  {
    $this->em = $em;
    $this->lockFactory = $lockFactory;
  }

  public function __destruct()
  {
    // To be honest, the locks will release automatically.
    // But we still release them manually, for ensurance.
    $this->release();
  }

  public function find(string $entityClass, int $id)
  {
    $randomKey = $entityClass . $id . uniqid();
    $lock = $this->lockFactory->createLock($randomKey, $ttl = 300);
    $this->locks[] += $lock;

    if ( ! $lock->acquire())
      return null;

    return $this->em->getRepo($entityClass)->find($id);
  }

  public function release()
  {
    foreach ($this->locks as $lock) {
      $lock->release();
    }
    $this->locks = [];
  }
}