Mark E. Segal

On-the-fly program modification: systems for dynamic updating

Several dynamic software-based updating systems that are in the research and production stages are described. In particular, the procedure-oriented dynamic updating system (PODUS) is discussed. In PODUS, a program is updated by loading the new version of the program and replacing each old procedure with its corresponding new procedure during execution. Updating a procedure involves changing the binding from its current version to the new version. When all procedures have been replaced by their corresponding new versions, the program update is completed.<<ETX>>

On dynamically updating a computer program: from concept to prototype

Abstract An approach to dynamically updating a computer program, i.e., updating while it is executing, is presented. Dynamic updating is crucial in applications where the cost of stopping and restarting the program makes doing so impractical. The presented system works with programs written in procedural languages such as Pascal and C. It is assumed that computer programs are written in a top-down manner consistent with good software engineering practices. Also assumed is that the underlying computer system logically provides a network-wide sparse virtual address space. Using these assumptions, it is possible to update computer programs with minimum interruption to the running program. By partitioning the address space into a number of version spaces, the handling of multiple simultaneous updates is possible. This allows one update to begin before previous updates complete. Via appropriate mapping mechanisms, old versions of procedures may call new procedures and maintain consistency. An overview of the design and implementation of a working prototype updating system is discussed and a sample updating session is illustrated.

Dynamically updating distributed software: supporting change in uncertain and mistrustful environments

A dynamic program updating system is a tool that replaces a running computer program with a new version, without stopping the currently running program. A method is described for extending an existing updating system to a distributed environment. These extensions allow distributed programs written using the remote procedure call paradigm to be dynamically updated. The approach scales to a geographically distributed computing environment and supports computer systems that contain heterogeneous hardware and software. Programs that execute on computer systems owned by multiple administrative entities can also be updated using this approach.<<ETX>>

Dynamic program updating: a software maintenance technique for minimizing software downtime

When a new version of a software system is created, the current version of the system must be shut down while the new version is installed, resulting in software ‘downtime’. There are application domains where such downtime is undesirable if not wholly unacceptable. A dynamic program updating system replaces, or updates, a computer program with a new version while the program continues to run. A dynamic program updating system for programs written in conventional procedural languages such as Pascal and C is described. The proposed system updates programs without causing substantial performance degradation and requires minimal user intervention to initiate the update. A fully functional prototype updating system is presented and a sample program, namely an internet packet router called the ‘Packet Pumper’, is updated. The performance of the updating system and the Packet Pumper is discussed.

Dynamic program updating in a distributed computer system

The authors present an approach to update a computer program dynamically (i.e., while it is executing). Such an approach is important in applications where the cost of stopping and restarting the program makes doing so impractical. The approach works with programs written in procedural languages such as Pascal, C, and Fortran, and it scales to a distributed computer system. The authors assume that computer programs are written in a top-down manner consistent with good software engineering practices. The also assume that the computer system logically provides a networkwide sparse virtual address space. The approach uses these assumptions to update computer programs in a distributed system with minimum interruption to the running program. An overview of the design and implementation of a prototype updating system is discussed, and future work is described.<<ETX>>

Join on a Cube: Analysis, Simulation, and Implementation

Our recent research effort has been in studying database processing on a cube connected multicomputer system. This paper discusses one part of our work, viz., the study of the join operation. Novel data redistribution operations are employed to improve the performance of the various database operations including join. Though a simple analysis is provided, the data redistribution operations are, in general, difficult to characterize analytically. Thus, a simulation and implementation was carried out to study the performance of these operations and the join operation. Issues involved in the simulation and implementation and a discussion of the results from both are presented in this paper.

Remediation of Application-Specific Security Vulnerabilities at Runtime

Researchers at Telcordia Technologies and the State University of New York, Stony Brook, are working on an approach that gives computer users new capabilities for defending against exploitation of application security vulnerabilities by allowing rapid development and deployment of real-time defenses. Their solution involves monitoring and changing an applications behavior by intercepting the system calls it requests.

The network modeling tool: a design aid for large-scale campus networks

A description is given of the network modeling tool (NetMod), which uses simple analytical models to provide the designers of large interconnected local area networks with an in-depth understanding of the potential performance of these systems. This tool will be useful in either a university, industrial, or governmental campus networking environment with thousands of computer sites. NetMod is implemented in easy-to-use Macintosh software packages, such as Microsoft Excel and HyperCard; a PC version of the tool will also be made available. The objectives of the tool, the analytical models, and its user interface are described in detail, along with its application to an actual campuswide network.<<ETX>>