Redis中Redisson红锁(Redlock)使用原理

RLock lock1 = redissonInstance1.getLock("lock1");
RLock lock2 = redissonInstance2.getLock("lock2");
RLock lock3 = redissonInstance3.getLock("lock3");
 
RedissonRedLock lock = new RedissonRedLock(lock1, lock2, lock3);
// 同时加锁：lock1 lock2 lock3
// 红锁在大部分节点上加锁成功就算成功。
lock.lock();
...
lock.unlock();

RedissonRedLock lock = new RedissonRedLock(lock1, lock2, lock3);
// 给lock1，lock2，lock3加锁，如果没有手动解开的话，10秒钟后将会自动解开
lock.lock(10, TimeUnit.SECONDS);
 
// 为加锁等待100秒时间，并在加锁成功10秒钟后自动解开
boolean res = lock.tryLock(100, 10, TimeUnit.SECONDS);
...
lock.unlock();

final List<RLock> locks = new ArrayList<>();


public RedissonMultiLock(RLock... locks) {
 if (locks.length == 0) {
  throw new IllegalArgumentException("Lock objects are not defined");
 }
 this.locks.addAll(Arrays.asList(locks));
}

public boolean tryLock(long waitTime, long leaseTime, TimeUnit unit) throws InterruptedException {
  long newLeaseTime = -1;
  if (leaseTime != -1) {
    newLeaseTime = unit.toMillis(waitTime)*2;
  }
 
  long time = System.currentTimeMillis();
  long remainTime = -1;
  if (waitTime != -1) {
    remainTime = unit.toMillis(waitTime);
  }
  long lockWaitTime = calcLockWaitTime(remainTime);
  
  int failedLocksLimit = failedLocksLimit();
  
  List<RLock> acquiredLocks = new ArrayList<>(locks.size());
  for (ListIterator<RLock> iterator = locks.listIterator(); iterator.hasNext();) {
    RLock lock = iterator.next();
    boolean lockAcquired;
    
    try {
      if (waitTime == -1 && leaseTime == -1) {
        lockAcquired = lock.tryLock();
      } else {
        long awaitTime = Math.min(lockWaitTime, remainTime);
        lockAcquired = lock.tryLock(awaitTime, newLeaseTime, TimeUnit.MILLISECONDS);
      }
    } catch (RedisResponseTimeoutException e) {
      // 如果抛出这类异常，为了防止加锁成功，但是响应失败，需要解锁所有节点
      unlockInner(Arrays.asList(lock));
      lockAcquired = false;
    } catch (Exception e) {
      // 抛出异常表示获取锁失败
      lockAcquired = false;
    }
   
    if (lockAcquired) {
      
      acquiredLocks.add(lock);
    } else {
      
      if (locks.size() - acquiredLocks.size() == failedLocksLimit()) {
        break;
      }

      if (failedLocksLimit == 0) {
        unlockInner(acquiredLocks);
        if (waitTime == -1 && leaseTime == -1) {
          return false;
        }
        failedLocksLimit = failedLocksLimit();
        acquiredLocks.clear();
        // reset iterator
        while (iterator.hASPrevious()) {
          iterator.previous();
        }
      } else {
        failedLocksLimit--;
      }
    }

    
    if (remainTime != -1) {
      remainTime -= System.currentTimeMillis() - time;
      time = System.currentTimeMillis();
      if (remainTime <= 0) {
        unlockInner(acquiredLocks);
        return false;
      }
    }
  }

  if (leaseTime != -1) {
    List<RFuture<Boolean>> futures = new ArrayList<>(acquiredLocks.size());
    for (RLock rLock : acquiredLocks) {
      RFuture<Boolean> future = ((RedissonLock) rLock).expireAsync(unit.toMillis(leaseTime), TimeUnit.MILLISECONDS);
      futures.add(future);
    }
   
    for (RFuture<Boolean> rFuture : futures) {
      rFuture.syncUninterruptibly();
    }
  }

  
  return true;
}