SCAJ Issue

1
SCA/J Issue 8Concurrency Model for Service
Reference Instances
www.oasis-open.org
Henning Blohm
2
Issue Statement

• TARGET Java Common Annotations and APIs
  specification, section "Java API" /
  "ComponentContext", "ServiceReference" and
  section "Asynchronous and Conversational
  Programming".
• DESCRIPTION While the current text says that a
  service reference represents a single
  conversation, it is not clear how a
  multi-threaded client should protect a
  non-conversational service reference's
  configuration (conversation id, callback, etc) so
  that it stays unmodified by other threads until
  an actual invocation is executed. Consider the
  following code snippet for example class
  AComponent   _at_Reference ItemCheckerService
  srv   void goCheckItem(long ticket, String
  itemId)         ServiceReference sr
  (ServiceReference) srv         sr.setConversatio
  nID(ticket)         srv.check(itemId)   
  A simple synchronization may lead to strict
  serialization of remote calls which is generally
  undesirable.

3
Previous Proposals

• P1 A service reference instance is actually a
  thread local proxy to the real reference
• () Foolproof for the simple cases
• (-) Cannot share conversation config between
  threads
• P2 A single service reference represents exactly
  one actual or potential conversation. Each call
  to ComponentContext.getService (and similar
  methods) returns a new instance of
  ServiceReference.
• () Still simple
• () Clear rule how to get to a new conversation
  and how to configure it (see sample below)
• (-) Injection not applicable for configurable
  refs
• Proposal Accept P2.

4
Sample 1
One conversation per call public interface
ItemChecker void check(String
id) public class AComponent _at_Context
ComponentContext ctx void goCheckItem(long
ticket, String itemId)
ServiceReferenceltItemCheckergt sr
ctx.getServiceReference(ItemChecker.class,
"checker") sr.setConversationID(ticket)
sr.getService().check(itemId)
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Sample 2
Conversation initiated once and used
often public class BComponent _at_Reference
ServiceReferenceltItemCheckergt checker
_at_Context ComponentContext ctx private
boolean configured public void
setTicket(long ticket) synchronized
(this) checker.setConversationID(ticket) this.c
onfiguredtrue void
goCheckItem(String itemId) synchronized
(this) if (!this.configured)
throw new IllegalStateException("not
configured missing ticket!")
checker.getService().check(itemId)

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Sample 3
It could be nice to have one more method on
ServiceReference public class CComponent
_at_Reference ServiceReferenceltItemCheckergt
checker void goCheckItem(long ticket,
String itemId) ServiceReferenceltItemChec
kergt sr checker.createNew()
sr.setConversationID(ticket)
sr.getService().check(itemId)