1. Event Service Outline Events Channels Event Services Examples

2. Event Event: occurrence of some sort, atomic
Event notification: actual data is transferred
Event-driven communication
Each notification is sent by a single supplier
Each notification may be delivered to potentially multiple consumers
Each consumer may receive multiple notifications from multiple suppliers
M-to-m communication
Communication partners are anonymous (implicit invocation)
Sending notification is nonblocking
Event notifications must be parsed and checked explicitly by consumer
Invocation-based communication
Event Service

3. Decoupling Supplier and Consumer
Special
Temporal
Syntactic
Semantic
Event Service

4. Decoupling Supplier and Consumer
The decoupling provides several important benefits:
Suppliers and consumers do not themselves physically have to handle the communication, nor must they have any specific knowledge of each other
Message passing between the supplier and consumer takes place asynchronously
Event channels will automatically buffer events they receive until a suitable consumer expresses interest in the events
Events may be confirmed and their delivery guaranteed if the vendor has implemented this capability
Suppliers can choose either to push events onto the channel (push) or have the channel itself to request events from them (pull)
Similarly choice for the consumer
A 1-to-1 correspondence between suppliers and consumers is not necessary: there can be multiple suppliers connected to a single consumer via the service, visa versa
Event Service

5. CORBA Event Service Concepts
Mediator Pattern
CollaboratingObject
ConcreateCollaborator1
ConcreateCollaborator2
ConcreteMediator
ConcreteMediator
Event Service

6. Push Model Communication
Supplier
Consumer
event
data
event flow
Event Service

7. Push Model Communication
Event channel push
push()
push()
Supplier
Event
Channel
Consumer
event
data
event
data
event flow
Event Service

8. Pull Model Communication
Supplier
Consumer
event
data
event flow
Event Service

9. Pull Model Communication
Event channel push
pull()
pull()
Supplier
Event
Channel
Consumer
event
data
event
data
event flow
Event Service

10. Mixed-Mode Communication
push()
push()
Supplier
Event
Channel
Consumer
event
data
event
data
pull()
event
data
pull()
Supplier
Consumer
event
data
event flow
Event Service

11. Event Flow Models Push Supplier Push Consumer Event Channel Pull
ProxyPushConsumer
ProxyPushSupplier
ProxyPullConsumer
ProxyPullSupplier
Pull
Supplier
pull()
pull()
Pull
Consumer
try_pull()
try_pull()
Event Direction
Event Service

12. Event Type
Typed
Untyped (Any)
Event Service

13. Interface Specifications: Module CosEventComm
exception Disconnected {};
interface PushConsumer {
void push (in any data) raises (Disconnected);
void disconnect_push_consumer (); };
interface PushSupplier {
void disconnect_push_supplier (); };
interface PullSupplier {
any pull () raises (Disconnected);
any try_pull (out boolean has_event) raises (Disconnected);
void disconnect_pull_supplier (); };
interface PullConsumer {
void disconnect_pull_consumer (); }; };
Event Service

14. Interface Specifications Module: CosEventChannelAdmin
exception AlreadyConnected {};
exception TypeError {};
interface ProxyPushConsumer: CosEventComm::PushConsumer {
void connect_push_supplier(in CosEventComm::PushSupplier push_supplier)
raises(AlreadyConnected); };
interface ProxyPullSupplier: CosEventComm::PullSupplier {
void connect_pull_consumer(in CosEventComm::PullConsumer pull_consumer)
raises(AlreadyConnected); };
interface ProxyPullConsumer: CosEventComm::PullConsumer {
void connect_pull_supplier(in CosEventComm::PullSupplier pull_supplier)
raises(AlreadyConnected,TypeError); };
interface ProxyPushSupplier: CosEventComm::PushSupplier {
void connect_push_consumer(in CosEventComm::PushConsumer push_consumer)
raises(AlreadyConnected, TypeError); }; };
Event Service

15. Interface Specifications Module: CosEventChannelAdmin
interface ConsumerAdmin {
ProxyPushSupplier obtain_push_supplier();
ProxyPullSupplier obtain_pull_supplier();};
interface SupplierAdmin {
ProxyPushConsumer obtain_push_consumer();
ProxyPullConsumer obtain_pull_consumer();};
interface EventChannel {
ConsumerAdmin for_consumers();
SupplierAdmin for_suppliers();
void destory();}; };
Event Service

16. Using an Event Channel
Client (Supplier or Consumer) first binds to the Event Channel (which must be created already)
Client obtains an Admin object from the Event Channel
Consumer needs ConsumerAdmin
Supplier needs SupplierAdmin
Client obtains an proxy object from the Admin object
ComsumerPloxy for Supplier client
SupplierProxy for Consumer client
Client adds the Supplier or Consumer to the Event Channel via a connect() call
Client and/or the Event Channel transfer data via the push(), pull(), and/or try_pull() calls
Event Service

17. An Example Printer Service push() Printer Supplier Event Channel event
data
pull()
Client
Consumer
event
data
event flow
Event Service

18. Printer Interface
module office {
enum Status { CANCELLED, PRINTED, ONLINE, OFFLINE, JAMMED, OUT_OF_PAPER };
typedef long JobID;
typedef string UserID;
struct Job {
JobID job_id;
UserID user_id; };
union PrinterStatus switch( Status ) {
case CANCELLED:
case PRINTED: Job the_job;
case OFFLINE:
case ONLINE: boolean dummy; };
interface Printer {
typedef string Document;
exception OffLine {};
exception AlreadyPrinted {};
exception UnknownJobID {};
JobID print(in Document text, in UserID uid)
raises (OffLine);
void cancel(in JobID id, in UserID uid)
raises (AlreadyPrinted, UnknownJobID);
void setOffLine(in boolean flag); };
The IDL definition does not contain event notification information.
Event Service