code: public Map<String, Set<ProviderInfo>> currentProviderMap() {
          providerLock.lock();
          try {
              Map<String, Set<ProviderInfo>> tmp = new LinkedHashMap<String, Set<ProviderInfo>>();
              tmp.put("alive", new HashSet<ProviderInfo>(aliveConnections.keySet()));
              tmp.put("subHealth", new HashSet<ProviderInfo>(subHealthConnections.keySet()));
              tmp.put("retry", new HashSet<ProviderInfo>(retryConnections.keySet()));
              tmp.put("uninitialized", new HashSet<ProviderInfo>(uninitializedConnections.keySet()));
              return tmp;
          } finally {
              providerLock.unlock();
          }
      }
docs: 获取当前的Provider列表（包括连上和没连上的）
  
  @return 当前的Provider列表 set