在Server WCF + Rest上处理长时间运行任务的最佳方法

We have a WCF + Rest service running on the host. I need to make a client call to the host that would initiate a long running task on the server (even up to 15 min), then check back once that process has finished to get the result. One solution is to have client checking the host every minute or so after the initial call - but that seems not very productive. Is there a way to expose some type of event through WCF so that client would be notified when the task completed on the server? What is the best approach for this type of scenario? thanksWe have a WCF + Rest service running on the hos