Use of CORBA in the PHENIX distributed online computing system

The PHENIX online control system is responsible for the configuration, control and monitoring of the PHENIX detector data acquisition system and ancillary control hardware, and the collection and archiving of the event data. The detector consists of 11 distinct subsystems, which are distributed physically and partitioned logically while ultimately being combined into a single operating unit. The online system consists of a large number of embedded commercial and custom processors as well as custom software processes which are involved in the collection, monitoring and control of the detector and the event data. These processing elements are distributed over a diverse set of computing platforms including VME based Power PC controllers, Pentium based NT systems, and SUN Solaris SPARC processors. CORBA has been adopted as the standard communication mechanism for PHENIX online system. This paper describes the design, implementation and use of CORBA to achieve a uniform and platform independent control environment while providing for the access, control and monitoring of the online detector elements over the distributed and diverse control environment. Synchronous and asynchronous communication issues are discussed as well as the development of CORBA compliant components which were developed to achieve client/server isolation and deterministic system behavior. The use and interaction between JAVA based clients and C++ based CORBA servers to further achieve a platform neutral environment are presented