References for Run-time Aggregate Selection with Strong Typing

Network packet processing often involves having the results of a database match or packet content search select the next program operation. Our packetC[1] language provides specialized aggregate data types,

databases

[2] for masked matching and

searchsets

[3] for packet payload search terms. It is common to chain operations on these types, so that the result of one operation selects the specific aggregate to use for the next operation. packetC offers a reference data type to support this kind of chaining. A packetC

reference

provides an abstract way to refer to one of the extended data type aggregates in source code. At runtime the reference construct’s value will indicate a particular aggregate of the relevant type. Thus, this construct is a classic

reference

in the computer science sense of a mechanism for indirect variable access. Unlike a C++ reference our construct must be assignable to support chaining that is driven by runtime results. Unlike a C-style pointer our reference must have strong typing, since runtime recovery from an illegal reference value (indicating a nonexistent or inappropriate aggregate) is not practical in this unforgiving, high-speed domain. The paper illustrates practical applications and shows that compressed code from using references does not cause performance penalties.