C++ Smart Pointers & Tags

摘要

Recovery of long-running, system-level daemons or services in the event of catastrophic failure is an important consideration in any software design of such processes. When these systems are written in C++ and use the reference-counted smart-pointer idiom, efficient recovery of smart pointers is critical to enable scalable recovery, and even correctness of its resumed operation. In this article, I describe a method to efficiently recover reference-counted pointers on software recovery after a shutdown. In particular, the method is memory efficient, avoiding object duplication, which results from traditional techniques of serialization and unserialization of references to pointers in C++. The technique uses tags to uniquely identify pointer objects when unserialized from an archive, an object cache to keep pointer references on recovery, and a method for smart pointers to impersonate other pointer objects.