Redis分佈式鎖實現原理 java版

說明：

Redis因爲是單線程的，所以本身沒有鎖的概念。

所以分佈式鎖的實現原理是往Redis當中寫入一個key(調用方法setnx)，寫入成功相當於獲取鎖成功。寫入失敗也即是setnx方法返回0，獲取鎖失敗。

注意鎖的失效時間，否則容易造成死鎖。

/**
  * 鎖在給定的等待時間內空閒，則獲取鎖成功 返回true， 否則返回false
  * @param subKey
  * @param timeout 如果timeout=0,取不到鎖時,不等待,直接返回.
  * @param unit
  * @return
  */
 public boolean tryLock(String subKey, long timeout, TimeUnit unit) {
  String key = LOCK_KEY + subKey;
  Jedis jedis = null;
  try {
   jedis = getConnection();
   if (jedis == null) {
    return Boolean.FALSE;
   }
   long nano = System.nanoTime();
   do {
    logger.debug("try lock key: " + key);
    Long i = jedis.setnx(key, key);
    if (i == 1) {
     jedis.expire(key, EXPIRED_TIME);
     logger.debug("get lock, key: " + key + " , expire in " + EXPIRED_TIME + " seconds.");
     return Boolean.TRUE;
    } else { // 存在鎖
     if (logger.isDebugEnabled()) {
      String desc = jedis.get(key);
      logger.debug("key: " + key + " locked by another business：" + desc);
     }
    }
    if (timeout == 0) { //取不到鎖時,不等待,直接返回.
     break;
    }
    Thread.sleep(200);
   } while ((System.nanoTime() - nano) < unit.toNanos(timeout));//取不到鎖時等待,直到timeout
   return Boolean.FALSE;
  } catch (JedisConnectionException je) {
   logger.error(je.getMessage(), je);
   returnBorkenConnection(jedis);
  } catch (Exception e) {
   logger.error(e.getMessage(), e);
  } finally {
   returnConnection(jedis);
  }
  return Boolean.FALSE;
 }


/**
  * 如果鎖空閒立即返回   獲取失敗 一直等待
  * @param subKey
  */
 public boolean lock(String subKey) {
  String key = LOCK_KEY + subKey;
  Jedis jedis = null;
  boolean isLock = false;
  try {
   jedis = getConnection();
   if (jedis == null) {
    return isLock;
   }
   while (true) {
    logger.debug("lock key: " + key);
    Long i = jedis.setnx(key, key);
    if (i == 1) {
     jedis.expire(key, EXPIRED_TIME);
     logger.debug("get lock, key: " + key + " , expire in " + EXPIRED_TIME + " seconds.");
     isLock = true;
    } else {
     if (logger.isDebugEnabled()) {
      String desc = jedis.get(key);
      logger.debug("key: " + key + " locked by another business：" + desc);
     }
     isLock = false;
    }
    Thread.sleep(500);
   }
  } catch (JedisConnectionException je) {
   logger.error(je.getMessage(), je);
   returnBorkenConnection(jedis);
  } catch (Exception e) {
   logger.error(e.getMessage(), e);
  } finally {
   returnConnection(jedis);
  }
  return isLock;
 }
/**
  * 釋放鎖
  * @param subKey
  */
 public void unLock(String subKey) {
  String key = LOCK_KEY + subKey;
  Jedis jedis = null;
  try {
   jedis = getConnection();
   if (jedis == null) {
    return;
   }
   jedis.del(key);
   logger.debug("release lock, keys :" + key);
  } catch (JedisConnectionException je) {
   logger.error(je.getMessage(), je);
   returnBorkenConnection(jedis);
  } catch (Exception e) {
   logger.error(e.getMessage(), e);
  } finally {
   returnConnection(jedis);
  }
 }