code: @Override
      public boolean returnConnection(Connection<CL> connection) {
          returnedCount.incrementAndGet();
          monitor.incConnectionReturned(host);
  
          ConnectionException ce = connection.getLastException();
          if (ce != null) {
              if (ce instanceof IsDeadConnectionException) {
                  noteError(ce);
                  internalCloseConnection(connection);
                  return true;
              }
          }
          errorsSinceLastSuccess.set(0);
  
          // Still within the number of max active connection
          if (activeCount.get() <= config.getMaxConnsPerHost()) {
              availableConnections.add(connection);
  
              if (isShutdown()) {
                  discardIdleConnections();
                  return true;
              }
          }
          else {
              // maxConnsPerHost was reduced. This may end up closing too many
              // connections, but that's ok. We'll open them later.
              internalCloseConnection(connection);
              return true;
          }
  
          return false;
      }
docs: Return a connection to this host
  
  @param connection