If some logic e.g. in a grails service should be invoked asynchronous, in Grails 2 the spring annotation @Async can be used. For that the spring annotation driven task support must be activated in the spring configuration. To activate the task support, the task namespace should be added to the spring configuration. Here a sample spring configuration ("resources.groovy").
Now the spring annotation can be used to mark e.g. service logic which should be invoked asynchronous.
Here a sample to send mails asynchronous (for sending the mails the grails mail plugin is used).
For more details see also the spring framework documentation: