Object Interconnections Overcoming Drawbacks in the OMG Events Service ( Column 10 )

Our last two columns have explored various techniques for using distributed callbacks to decouple clients and servers and create peer-to-peer relationships between the objects in a distributed system. We’ve shown various ways to eliminate the polling required by a stock application client. All these approaches center around direct or indirect callbacks from the Stock Quote Server. Like all engineering solutions, the designs and implementations we’ve shown have their strengths and weaknesses. Our last column investigated how to use the OMG Events Service to implement a stock quote callback mechanism. The OMG Events Service is defined in Volume 1 of the OMG Common Object Services (COS) Specification [1]. The following event delivery models are supported by Event Channels: Canonical Push model: The active event Supplier (in our case, the Stock Quote Server) pushes events to the Event Channel, which in turn pushes them to passive event Consumers (in our case, interested stock quote client applications). Canonical Pull model: The active event Consumers pull events from the Event Channel, which in turn pulls them from the passive event Supplier. Hybrid Push/Pull model: The active event Supplier pushes events to the Event Channel, while the active event Consumers pull events from the Event Channel. Hybrid Pull/Push model: The Event Channel pulls events from the passive event Supplier and pushes them to passive event Consumers.