1. CORBA Event Service Martin Senger senger@ebi.ac.uk

2. What are the goals... exchanging data between two and more objects exchanging data between objects that do not know about each other a special case: asynchronous execution of an operation

3. What data are being exchanged “Untyped” data –usual case –data are wrapped in Any’s –which means: data of any but known type Typed data –objects are not purely unknown to each other –CosEvent specification is a bit under-specified –my opinion: it’s a bit cheating

4. How to achieve the goals Event Channel Data consum er Data consum er Data consum er Data supplier Data supplier Data supplier Data supplier Data supplier

5. Event Channel it is just another object it does not know what data it transfers –no filtering depending on data contents it behaves democratically –no filtering depending on suppliers/consumers two main functions –it registers event suppliers and consumers, –and it carries data for or from them which may be done cleverly (like keeping messages for not-(yet)-present consumers)

6. How to carry the data: Push Model I am a supplier. I have a data to be sent around. I wish to decide when the data are sent. Just let me know whom to send it. I am a consumer. I need data to be able to do something with them. I wish to wait for data. I will not take any initiative, just call my method when you have data for me. Data Initiative Push Supplier Push Consumer

7. How to carry the data: Pull Model I am a supplier. I have a data to be sent around. I wish to wait for those interested in my data. I will not take any initiative, just call my method when you want data I am a consumer. I need data to be able to do something with them. I wish to decide when to go for data. Just let me know where I can ask for data. Data Initiative Pull Supplier Pull Consumer

8. Two roles of user objects Supplier vs. Consumer –who has data and who wants data –data always go from suppliers to consumers Active vs. Inactive participant –active guys ( “PullConsumer” and “PushSupplier” ) do not need many methods because they actively call methods of passive guys –passive guys ( “PushConsumer” and “PullSupplier” ) need to have methods that are called; they are designed as “callback” objects

9. But where is the Event Channel? I am a supplier. And I am pushing data I am a consumer. And I am pulling data InitiativeInitiative I am a supplier. And I am waiting to give data I am a consumer. And I am waiting for data InitiativeInitiative

10. So what is the Event Channel for? a mediator of antagonistic initiatives a multiplier of data events (one supplier for more consumers) …and vice-versa (more suppliers for one consumer) a provider of “quality of service” –storing messages, re-sending them, etc. –but this is not part of CosEvent Service interfaces

11. What you need to do create your suppliers and/or consumers –application specific task register them and register their behaviour –two steps registration to obtain a proxy supplier/consumer, and to connect to it to do it, however, you need an Event Channel –interface to a factory of Event Channels is not standardised

12. SupplierAdmin for_suppliers() ConsumerAdmin for_consumers() void destroy() EventChannel ProxyPushConsumer obtain_push_consumer() ProxyPullConsumer obtain_pull_consumer() SupplierAdmin I am a suppli er I am a consu mer PushSupplier void push(in any data) PushConsumer ProxyPushSupplier obtain_push_supplier() ProxyPullSupplier obtain_pull_supplier() ConsumerAdmin usually provided by a service written in your application void connect_push_supplier(in PushSupplier) ProxyPushConsumer active mode void connect_pull_supplier(in PullSupplier) ProxyPullConsumer passive mode disconnect methods are not shown any pull() any try_pull (out boolean has_event() PullSupplier connect_push_consumer(in PushConsumer) ProxyPushSupplier passive mode void connect_pull_consumer(in PullConsumer) ProxyPullSupplier active mode PullConsumer

13. A code example: PushSupplier // registration SupplierAdmin supplierAdmin = eventChannel.for_suppliers(); ProxyPushConsumer consumer = supplierAdmin.obtain_push_consumer(); consumer.connect_push_supplier (null); // sending data consumer.push (data); // diconnecting consumer.disconnect_push_consumer();

14. A code example: PushConsumer // my implementation of a PushConsumer (receiving data) public class PushConsumerImpl extends _PushConsumerImplBase { public void push (Any any) {…} public void disconnect_push_consumer() {…} } // registration & connecting my implementation as a visible object PushConsumerImpl consumer = new PushConsumerImpl(…); orb.connect (consumer); ConsumerAdmin consumerAdmin = eventChannel.for_consumers(); ProxyPushSupplier supplier = consumerAdmin.obtain_push_supplier(); consumer.connect_push_supplier (consumer); // waiting for incoming requests boa.impl_is_ready (null);

15. From-the-shelf implementations CosEvent Service as a standalone product EventChannelFactory usually provides “Default” EventChannel creates A non-standard interface (an example) interface EventChannelFactory { EventChannel create_channel (in string id) raises (ChannelAlreadyExists); EventChannel get_channel_by_id (in string id) raises (ChannelNotAvailable); …get_channels… …shutdown()... An application using COSEvent Service

16. There are other issues... Typed event communication –objects call operations on other objects using some mutually agreed interface Notification Service

17. Notes for hands-on go to directory EventService play with –java TalkToMe -help change class EventExchanger to use different push/pull model