Software aging

In software engineering, software aging refers to all software's tendency to fail, or cause a system failure after running continuously for a certain time. As the software gets older it becomes less immune and will eventually stop functioning as it should, therefore rebooting or reinstalling the software can be seen as a short term fix. A proactive fault management method to deal with the software aging incident is software rejuvenation. This method can be classified as an environment diversity technique that usually is implemented through software rejuvenation agents (SRA).Software failures are a more likely cause of unplanned systems outages compared to hardware failures. This is because software exhibits over time an increasing failure rate due to data corruption, numerical error accumulation and unlimited resource consumption. In widely used and specialized software, a common action to clear a problem is rebooting because aging occurs due to the complexity of software which is never free of errors. It is almost impossible to fully verify that a piece of software is bug-free. Even high-profile software such as Windows and macOS must receive continual updates to improve performance and fix bugs. Software development tends to be driven by the need to meet release deadlines rather than to ensure long-term reliability. Designing software that can be immune to aging is difficult. Not all software will age at the same rate as some users use the system more intensively than others.In systems that use an OS user programs have to request memory blocks in order to perform an operation. After this operation (e.g. a subroutine) is completed, the program is expected to free up all the memory blocks allocated for it in order to make it available to other programs for use. In programming languages without a garbage collector (e.g. C and C++) it's up to the programmer to call the necessary memory releasing functions and to account for all the unused data within the program. However this doesn't always happen. Due to software bugs the program might consume more and more memory eventually causing the system to run out of memory. In low memory conditions, the system usually functions slower due to the performance bottleneck caused by intense swapping (thrashing), applications become unresponsive and those that request large amounts of memory unexpectedly may crash. In case the system runs out of both memory and swap even the OS might crash causing the whole system to reboot.Two methods for implementing rejuvenation are:Garbage collection is a form of automatic memory management whereby the system automatically recovers unused memory. For example, the .NET Framework manages the allocation and release of memory for software running under it. But automatically tracking these objects takes time and is not perfect.