protected function changeState($state)
    {
        $currState = $this->_poolClientState;
        //Save previous state
        if (isset($currState) && $currState !== PoolClientInterface::CLIENT_POOL_STATE_LOCKED) {
            $this->_poolClientStatePrev = $currState;
        }
        $this->_poolClientState = $state;
        $this->emit(PoolClientInterface::CLIENT_POOL_EVENT_CHANGE_STATE, [$state]);
    }