High Performance CORBA

The object communication architecture as standardised by the OMG does not address any performance requirements. When applying this technology to performance critical applications such as avionics[GS98c] or real-time control[PWP98], it became clear that some effort has to be made towards making CORBA implementations more efficient[YS98]. Efficiency here means deterministic behaviour of the ORB in terms of scale, speed and memory consumption. These are prerequisites for building CORBA components that support application environments with special demands. Unfortunately only few efforts concentrating at CORBA for real-time environments have shown significant impact on further development. Two examples of high-performance CORBA projects that are worth mentioning are the COOL and the TAO systems:

• Chorus/COOL - Although already designed and implemented in late 1988 for the Chorus real-time operating system, COOL has been redesigned several times to be compliant with the CORBA architecture[HM90]. It focuses on being efficient in terms of upcall latency and small memory footprint[JHJ$^$94, p.5]. Not only have these goals been achieved[Sys93][SMFGG98], but the modular design also allows ports to other operating systems, such as WindowsNT and Solaris[Sys96, p.2]. The work on Chorus/COOL also resulted in contribution to the OMG Minimum CORBA specification[Gro97a] and the OMG CORBA real-time efforts[Sys97]. Chorus and COOL are now commercial products, maintained by Sun Microsystems.

• TAO (The ACE ORB) - TAO[SGH$^$97] is an ORB based on the ADAPTIVE Communication Environment (ACE)[Sch94,SLM88]. ACE is an object oriented toolkit providing an operating system abstraction layer and building blocks for network programming. ACE is written entirely in C++ and aims at efficient implementation of design patterns for programming distributed systems. TAO makes heavy use of these patterns[SLC99,SC99,POS$^$99,SC97], thus resulting in a highly configurable middleware system. Not only concurrency policies are freely exchangeable at runtime, but also ORB resources that affect the way in which servants are located and invoked[GS97b]. TAO can be configured to work with different communication subsystems[GS98a]. It is however not possible to mix these pluggable transport components. Its internals are well documented and evaluated. Information about concurrency mechanisms used for handling an increasing amount of clients[Sch98], alleviation from performance limitations in the server[SG99] and scheduling issues[GLSK99,SMFGG98,HLS97] for real-time applications are presented in numerous publications[LFGS99,SBL$^$97,GS97a,GHSP96]. This rich set of documentation allows us to use TAO as a subject for investigating possible CORBA application.