Object Interconnections Collocation Optimizations for CORBA ( Column 18 )

In this column, we take break from our ongoing discussion of the CORBA Messaging specification to cover collocation, which is an important topic for component-based application developers. Collocation is a technique for transparently optimizing communication overhead when clients and servants are configured into the same address space. For instance, Microsoft COM [1] applications frequently use collocation to access so-called “in-proc” components. Unlike COM, which evolved from its original collocated component model into a networked component model, CORBA is often considered to be a distributed object computing model. However, there are situations where clients and servants must be configured in the same address space [2]. For example, user-supplied ServantManagers are ordinary CORBA objects that are invoked by POAs to help incarnate servants [3]. In such cases, CORBA ORBs can transparently employ collocation optimizations to ensure there’s no unnecessary overhead of (de)marshaling data or transmitting requests/replies through a “loopback” communication device. In this column, we describe and evaluate several collocation techniques. To make the discussion concrete, we describe how collocation is supported in TAO [4], which is an ORB developed at Washington University, St. Louis. Finally, we present benchmarking results that compare the relative performance gains from various types of collocation strategies and optimizations.