Complex sentence: Computer programs may manage their own resources by using features exposed by programming languages (is a survey article contrasting different approaches), or may elect to manage them by a host--an operating system or virtual machine--or another program.
Split into simpler sentences: Computer programs may manage their own resources, and there are various techniques for resource management, depending on the programming language; is a survey article contrasting different approaches. Alternatively, they can be managed by a host--an operating system or virtual machine--or another program.