Add channel for event-handlers

[XinyueZ]

Thanks for merge last pull-req.

I add channels on go-routines for some reasons.

Current "handler"s are all event-handlers delegated by go-routine, that's nice. However,
it doesn't work for some long-time jobs like a network call on webservver(i.e GAE).
Add boolean channel to construct cocurrency for such jobs.

The channel is boolean for success or failed status inside go-routine.

Think about it, it might be useful.