Some of our IOs create external resources that need to be cleaned up when a pipeline is terminated. It looks like the org.apache.beam.sdk.io.UnboundedSource interface is called on creation, but there is no call for cleanup. For example, PubsubIO creates a Pubsub subcription in createReader()/split() and it should be deleted at shutdown. Does anyone have ideas on how I might make this happen?
(I filed https://issues.apache.org/jira/browse/BEAM-5051 tracking the PubSub specific issue.) Andrew
