framework/base/Application.php
public function setRuntimePath($path)
    {
        $this->_runtimePath = Yii::getAlias($path);
        Yii::setAlias('@runtime', $this->_runtimePath);
    }
public function setRuntimePath($path)
    {
        $this->_runtimePath = Yii::getAlias($path);
        Yii::setAlias('@runtime', $this->_runtimePath);
    }
Sets the directory that stores runtime files.
@param string $path the directory that stores runtime files.