Add a callback for notifications.
Remove callback for notifications.
Returns the request object that was used to initialize this handle. Never null.
Returns a response if this handle has finished execution, otherwise returns null.
Returns a status object for the current execution. This will likely be the same object that would be returned as a component of the Response value. Never null.
Attempts to cancel execution of this Request. Returns true if cancellation was successful. Returns false if not, in which case likely this request will run to completion.
Closes this handle. If the request is running, then a cancellation will be attempted first. All uses of a handle should be surrounded by a try/finally close block.