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I had the privilege of attending CPPCON last month. Michael Wong, Maged Michael, and I presented a parallel-programming overview, in which I presented the "Hardware and its Habits" chapter of Is Parallel Programming Hard, And, If So, What Can You Do About It?.

But the highlight for me was actually sitting in the audience for a pair of talks by people who had implemented RCU in C++.

Ansel Sermersheim presented a two-part talk entitled Multithreading is the answer. What is the question?. The second part of this talk covered lockless containers, and used a variant of RCU to implement a low-overhead libGuarded facility in order to more easily avoid deadlocks. The implementation is similar to the Linux-kernel real-time RCU implementation by Jim Houston and Joe Korty in that the counterpart to rcu_read_unlock() actively registers a quiescent state. Ansel's implementation goes further by also driving callback invocation from rcu_read_unlock(). Now I don't recommend this for a general-purpose RCU implementation due to the possibility of deadlock should a resource need to be held across rcu_read_unlock() and acquired within the callback. However, this approach should work just fine in the case where the callbacks just free memory and the memory allocator does not contain too many RCU read-side critical sections.

Fedor Pikus presented a talk entitled Read, Copy, Update, then what? RCU for non-kernel programmers, in which he gave a quite-decent introduction to use of RCU. This introduction included an improved version of my long-standing where-to-use-RCU diagram, which I fully intend to incorporate. I had a number of but-you-could moments, including the usual "put the size in with the array" advice, ways of updating things already exposed to readers, and the fact that RCU really can tolerate multiple writers, along with some concerns about counter overflow. Nevertheless, an impressive amount of great information in a one-hour talk!

It is very good to see more people making use of RCU!