Dynamic program updating: A software maintenance technique for minimizing software, downtime

SUMMARY When a new version of a sonware 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 undesirahle 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. Software maintenance research has traditionally addressed the question 'What can researchers, softwarc engineers, programmers and managers do to make programs more adaptable to the changing environments in which they must exist?' Adaptability (and thus maintainability) encompasses many issues including good initial program design, well-written program code, powerful development and maintenance tools, adequate documentation , and supportive management to encourage proper use of these resources. One question that has not been given substantial attention in the software maintenance literature is 'Having used the available software maintenance tools to enhance a program, ' 'Environment' encompasses both the tasks that the program must perform and the interactions with other (possibly rcal-world) entities.