code: protected Map<ProviderInfo, ClientTransport> clearProviders() {
          providerLock.lock();
          try {
              // 当前存活+重试的
              HashMap<ProviderInfo, ClientTransport> all = new HashMap<ProviderInfo, ClientTransport>(aliveConnections);
              all.putAll(subHealthConnections);
              all.putAll(retryConnections);
              all.putAll(uninitializedConnections);
              subHealthConnections.clear();
              aliveConnections.clear();
              retryConnections.clear();
              uninitializedConnections.clear();
              return all;
          } finally {
              providerLock.unlock();
          }
      }
docs: 清空服务列表
  
  @return 带回收的服务列表