Reference Implementation: xEvents

xEvents is a reference implementation of the Grid SOAP Events framework. It is implemented in both C++ and Java. It uses SoapRMI [2] as the underlying communication substrate. SoapRMI layers a C++ and Java based RMI system on top of SOAP RPC, allowing the two languages to interoperate in messaging.

The following are some of the salient features of xEvents:

• Publishers and Subscribers: xEvents contains example implementations for simple publisher and listener. Support for leasing publisher also exists in xEvents.
• Event Channel and Remote Reference: SoapRMI has built in support for remote references. xEvents leverages it to transparently pass event listeners as remote references on the wire. An event channel is implemented as a remote interface to support subscription and dispersal of events.
• Naming: xEvents uses the JNDI interface to access LDAP to store remote references. It can also use SoapRMI registries provided by SoapRMI.
• Firewall: To make remote objects such as a publisher or listener residing behind a firewall accessible, xEvents (Java implementation) uses a tunnel or HTTP proxy that redirects the request to remote objects. Event channels or listeners that reside behind firewalls should bind the URL of the proxy server to the LDAP repository instead of their own IP address. Java provides support for HTTP proxy that is used by xEvents publishers that reside behind firewalls.