Study On Invocation Technology Of Component Platform And The Applications

The rapid progress of network technology and the idea ofcomponent-based software design pattern bring distributed componenttechnology to wide use. Currently, CORBA, DCOM, EJB and UNO arepopular distributed component technologies, and each of them has its ownmerits and disadvantages. The interoperability of components is implementedthrough the invocation of interface in object-orient component technology.The relation of caller and component object follows client/server model.Caller is located on client end and component object is located on server end.There are two transfer modes that can be used in the process of invocation:request/response mode and publish/subscribe mode.This paper studies on invocation technology through TH_COREcomponent platform developed by us. TH_CORE is a light-weight componentplatform, providing particular functions such as supporting SOAP messagesand caching mechanism, packaging self-describing information in componentsand so on. TH_CORE interface has a double-pointer structure in memory.TH_CORE adopt proxy and stub to accomplish the marshaling andunmarshaling of parameters and the transfer of invocation data duringcross-process invocation. IChannel is the interface to provide invocation datatransfer in TH_CORE, and it contains operation both for server end and forclient end. Three implementations of IChannel are provided by TH_CORE,including transfer through SOAP, FIFO and TCP. They have differentperformance and function fields.Then, this paper develops event mechanism on TH_CORE according toconnectable object model. In connectable object model, events are defined inevent interface on server end, event container takes charge of the managementof event interfaces and the firing of events, and client end establishes theconnection to server end by sink object. Connectable object model hasextensible structure. This paper raises optimization design of connectableobject model, and designs TH_CORE event model on it. In TH_CORE eventmodel, each event is attached with timestamps, and recognizer can judgerelationship between events by the timestamps in order to recognizecomposite events. And an event queue is used to support priority eventtransfer. XML-based description of composite events is also provided inTH_CORE event model.PURPLE is a middleware platform established on TH_CORE withreflective architecture. This paper implements the system hardwareenvironment monitor system in PURPLE with TH_CORE event mechanism.Probe Container and Info Container are used to monitor system condition.Probe Container loads a set of Probes to get information of system condition,and sends the information to Info Container. Info Container loads a set ofEvent Containers, and implements the modification of system configurationpolicy according to environment information through Event Containers. ProbeContainer and Info Container both have extensible architecture, and they canbe reconfigured dynamically.There is the summary of work and the expectation of next step at the endof this paper.