Dynamic software updates for C applications

A common inconvenience of keeping a computer system’s installed applications updated is the loss of the availability of services while the respective application is updating. Typically, the user has a hard choice to make: Accept the downtime or pay the cost of a redundant system. Many regular applications are not well suited to be run in a truly redundant way, but even when a redundant system is available, updating carries the risk of total loss of service in case of a failure in the part which remains online. This article presents a solution in the form of Dynamic Software Updates for applications written in C. Several implementations of dynamic software updates are discussed, and their applicability to some common applications is explored. The tools necessary to create patches between versions are also scrutinized, along with performance characteristics of the individual approaches and the required time to conduct an update. Special attention is given to applications employing concurrency, as the added complexity of threads which are interacting with each other needs to be addressed to guarantee the safety of an update process.