Homework: Read-Copy-Update

Read: Read-Copy Update paper

Hand-In Procedure

You are to turn in this homework before lecture. Please email your answers to 6.828-homework@pdos.csail.mit.edu, preferably in plain text.

Read-Copy Update

This paper describes an approach to eliminating read locks from data structures that obey certain properties. RCU has been used in various subsystems of Linux (there are even graphs of RCU usage in Linux).

Submit: The paper describes how they applied RCU techniques to Linux's file descriptor arrays. Why it safe for read-only access to the file descriptor arrays to proceed without taking locks when RCU is used to expand file descriptor arrays? Why are read-only operations that are operating on the "old" version of an array not in danger of accessing freed memory?