This paper describes the design and performance of the J-Server, an integrated web and telephony server that allows untrusted Java servlets to be dynamically uploaded to extend the server''s functionality. The J-Kernel provides for protection and communication between J-Server servlets, and ensures that servlets can be cleanly terminated. A resource monitor called JRes is used to account for servlet resource usage. Two sample applications show that the overhead of J-Kernel task boundary crossings is small compared to the applications'' overall running time. Experience developing applications for the J-Server demonstrates the benefits of extensible systems based on safe language protection, and the flexibility of the servlet model.

RPC has established itself as one of the more powerful communication paradigms for distributed computing. In recent years, object-oriented languages have impacted RPC semantics, with a number of variants providing remote method invocation and various forms of distributed object systems. At the same time, performance has changed little with the bottleneck being the network transport, in particular the in-kernel protocol implementations. This paper describes J-RPC, an RPC architecture that leverages user-level network interfaces (UNI) to circumvent the kernel on the critical path. It describes how the wire format and the RPC system can be engineered to allow zero-copy reception of Java objects and zero-copy transmission of arrays. All objects received are fully type-checked and can be directly used by the receiving program. The design is connection-oriented for performance and leverages the JVM''s garbage collector when managing receive buffers. An implementation built from an off-the-shelf JVM and a commercial UNI is used to evaluate the architecture and the tradeoffs of type-safe, zero-copy data marshaling.

MATLAB, a commercial product of The MathWorks, Inc., has become one of the principal languages of desktop scientific computing. A system is described that enables one to run MATLAB conveniently on multiple processors. Using short, MATLAB-style commands like Eval, Send, Recv, Bcast, Min, and Sum, the user operating within one MATLAB session can start MATLAB processes on other machines and then pass commands and data between between these various processes in a fashion that maintains MATLAB''s traditional user-friendliness. Multi-processor graphics is also supported. The system currently runs under MPICH on an IBM SP2 or a network of Unix workstations, and extensions are planned to networks of PCs. MultiMATLAB is potentially useful for education in parallel programming, for prototyping parallel algorithms, and for fast and convenient execution of easily parallelizable numerical computations on multiple processors.

This technical report describes the design, implementation, and evaluation of Active Messages on the IBM SP-2. The implementation benchmarked here uses the standard TB2 network adapter firmware but does not use any IBM software on the Power2 processor. We assume familiarity with the concepts underlying Active Messages. The main performance characteristics are a one-word message round-trip time of 51.0 $\mu$s and an asymptotic network bandwidth of 34.3 MB/s. After presenting selected implementation details, the paper focuses on detailed performance analysis, including a comparison with IBM''s Message Passing Layer (MPL) and Split-C benchmarks.